| 1 | .TH LIBPNG 3 "April 14, 2019"
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| 2 | .SH NAME
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| 3 | libpng \- Portable Network Graphics (PNG) Reference Library 1.6.37
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| 4 |
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| 5 | .SH SYNOPSIS
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| 6 | \fB#include <png.h>\fP
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| 7 |
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| 8 | \fBpng_uint_32 png_access_version_number (void);\fP
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| 9 |
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| 10 | \fBvoid png_benign_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
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| 11 |
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| 12 | \fBvoid png_build_grayscale_palette (int \fP\fIbit_depth\fP\fB, png_colorp \fIpalette\fP\fB);\fP
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| 13 |
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| 14 | \fBpng_voidp png_calloc (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
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| 15 |
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| 16 | \fBvoid png_chunk_benign_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
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| 17 |
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| 18 | \fBvoid png_chunk_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
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| 19 |
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| 20 | \fBvoid png_chunk_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
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| 21 |
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| 22 | \fBvoid png_convert_from_struct_tm (png_timep \fP\fIptime\fP\fB, struct tm FAR * \fIttime\fP\fB);\fP
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| 23 |
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| 24 | \fBvoid png_convert_from_time_t (png_timep \fP\fIptime\fP\fB, time_t \fIttime\fP\fB);\fP
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| 25 |
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| 26 | \fBpng_charp png_convert_to_rfc1123 (png_structp \fP\fIpng_ptr\fP\fB, png_timep \fIptime\fP\fB);\fP
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| 27 |
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| 28 | \fBpng_infop png_create_info_struct (png_structp \fIpng_ptr\fP\fB);\fP
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| 29 |
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| 30 | \fBpng_structp png_create_read_struct (png_const_charp \fP\fIuser_png_ver\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fIwarn_fn\fP\fB);\fP
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| 31 |
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| 32 | \fBpng_structp png_create_read_struct_2 (png_const_charp \fP\fIuser_png_ver\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fP\fIwarn_fn\fP\fB, png_voidp \fP\fImem_ptr\fP\fB, png_malloc_ptr \fP\fImalloc_fn\fP\fB, png_free_ptr \fIfree_fn\fP\fB);\fP
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| 33 |
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| 34 | \fBpng_structp png_create_write_struct (png_const_charp \fP\fIuser_png_ver\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fIwarn_fn\fP\fB);\fP
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| 35 |
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| 36 | \fBpng_structp png_create_write_struct_2 (png_const_charp \fP\fIuser_png_ver\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fP\fIwarn_fn\fP\fB, png_voidp \fP\fImem_ptr\fP\fB, png_malloc_ptr \fP\fImalloc_fn\fP\fB, png_free_ptr \fIfree_fn\fP\fB);\fP
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| 37 |
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| 38 | \fBvoid png_data_freer (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIfreer\fP\fB, png_uint_32 \fImask\fP\fB);\fP
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| 39 |
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| 40 | \fBvoid png_destroy_info_struct (png_structp \fP\fIpng_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
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| 41 |
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| 42 | \fBvoid png_destroy_read_struct (png_structpp \fP\fIpng_ptr_ptr\fP\fB, png_infopp \fP\fIinfo_ptr_ptr\fP\fB, png_infopp \fIend_info_ptr_ptr\fP\fB);\fP
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| 43 |
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| 44 | \fBvoid png_destroy_write_struct (png_structpp \fP\fIpng_ptr_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
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| 45 |
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| 46 | \fBvoid png_err (png_structp \fIpng_ptr\fP\fB);\fP
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| 47 |
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| 48 | \fBvoid png_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
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| 49 |
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| 50 | \fBvoid png_free (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
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| 51 |
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| 52 | \fBvoid png_free_chunk_list (png_structp \fIpng_ptr\fP\fB);\fP
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| 53 |
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| 54 | \fBvoid png_free_default (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
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| 55 |
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| 56 | \fBvoid png_free_data (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fInum\fP\fB);\fP
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| 57 |
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| 58 | \fBpng_byte png_get_bit_depth (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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| 59 |
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| 60 | \fBpng_uint_32 png_get_bKGD (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_16p \fI*background\fP\fB);\fP
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| 61 |
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| 62 | \fBpng_byte png_get_channels (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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| 63 |
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| 64 | \fBpng_uint_32 png_get_cHRM (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, double \fP\fI*white_x\fP\fB, double \fP\fI*white_y\fP\fB, double \fP\fI*red_x\fP\fB, double \fP\fI*red_y\fP\fB, double \fP\fI*green_x\fP\fB, double \fP\fI*green_y\fP\fB, double \fP\fI*blue_x\fP\fB, double \fI*blue_y\fP\fB);\fP
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| 65 |
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| 66 | \fBpng_uint_32 png_get_cHRM_fixed (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*white_x\fP\fB, png_uint_32 \fP\fI*white_y\fP\fB, png_uint_32 \fP\fI*red_x\fP\fB, png_uint_32 \fP\fI*red_y\fP\fB, png_uint_32 \fP\fI*green_x\fP\fB, png_uint_32 \fP\fI*green_y\fP\fB, png_uint_32 \fP\fI*blue_x\fP\fB, png_uint_32 \fI*blue_y\fP\fB);\fP
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| 67 |
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| 68 | \fBpng_uint_32 png_get_cHRM_XYZ (png_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, double \fP\fI*red_X\fP\fB, double \fP\fI*red_Y\fP\fB, double \fP\fI*red_Z\fP\fB, double \fP\fI*green_X\fP\fB, double \fP\fI*green_Y\fP\fB, double \fP\fI*green_Z\fP\fB, double \fP\fI*blue_X\fP\fB, double \fP\fI*blue_Y\fP\fB, double \fI*blue_Z\fP\fB);\fP
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| 69 |
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| 70 | \fBpng_uint_32 png_get_cHRM_XYZ_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_fixed_point \fP\fI*int_red_X\fP\fB, png_fixed_point \fP\fI*int_red_Y\fP\fB, png_fixed_point \fP\fI*int_red_Z\fP\fB, png_fixed_point \fP\fI*int_green_X\fP\fB, png_fixed_point \fP\fI*int_green_Y\fP\fB, png_fixed_point \fP\fI*int_green_Z\fP\fB, png_fixed_point \fP\fI*int_blue_X\fP\fB, png_fixed_point \fP\fI*int_blue_Y\fP\fB, png_fixed_point \fI*int_blue_Z\fP\fB);\fP
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| 71 |
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| 72 | \fBpng_uint_32 png_get_chunk_cache_max (png_const_structp \fIpng_ptr\fP\fB);\fP
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| 73 |
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| 74 | \fBpng_alloc_size_t png_get_chunk_malloc_max (png_const_structp \fIpng_ptr\fP\fB);\fP
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| 75 |
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| 76 | \fBpng_byte png_get_color_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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| 77 |
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| 78 | \fBpng_uint_32 png_get_compression_buffer_size (png_const_structp \fIpng_ptr\fP\fB);\fP
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| 79 |
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| 80 | \fBpng_byte png_get_compression_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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| 81 |
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| 82 | \fBpng_byte png_get_copyright (png_const_structp \fIpng_ptr\fP\fB);\fP
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| 83 |
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| 84 | \fBpng_uint_32 png_get_current_row_number \fI(png_const_structp\fP\fB);\fP
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| 85 |
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| 86 | \fBpng_byte png_get_current_pass_number \fI(png_const_structp\fP\fB);\fP
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| 87 |
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| 88 | \fBpng_voidp png_get_error_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
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| 89 |
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| 90 | \fBpng_byte png_get_filter_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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| 91 |
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| 92 | \fBpng_uint_32 png_get_gAMA (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, double \fI*file_gamma\fP\fB);\fP
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| 93 |
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| 94 | \fBpng_uint_32 png_get_gAMA_fixed (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fI*int_file_gamma\fP\fB);\fP
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| 95 |
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| 96 | \fBpng_byte png_get_header_ver (png_const_structp \fIpng_ptr\fP\fB);\fP
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| 97 |
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| 98 | \fBpng_byte png_get_header_version (png_const_structp \fIpng_ptr\fP\fB);\fP
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| 99 |
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| 100 | \fBpng_uint_32 png_get_eXIf (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fI*exif\fP\fB);\fP
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| 101 |
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| 102 | \fBpng_uint_32 png_get_eXIf_1 (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_unit_32 \fP\fI*num_exif\fP\fB, png_bytep \fI*exif\fP\fB);\fP
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| 103 |
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| 104 | \fBpng_uint_32 png_get_hIST (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_16p \fI*hist\fP\fB);\fP
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| 105 |
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| 106 | \fBpng_uint_32 png_get_iCCP (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_charpp \fP\fIname\fP\fB, int \fP\fI*compression_type\fP\fB, png_bytepp \fP\fIprofile\fP\fB, png_uint_32 \fI*proflen\fP\fB);\fP
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| 107 |
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| 108 | \fBpng_uint_32 png_get_IHDR (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*width\fP\fB, png_uint_32 \fP\fI*height\fP\fB, int \fP\fI*bit_depth\fP\fB, int \fP\fI*color_type\fP\fB, int \fP\fI*interlace_type\fP\fB, int \fP\fI*compression_type\fP\fB, int \fI*filter_type\fP\fB);\fP
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| 109 |
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| 110 | \fBpng_uint_32 png_get_image_height (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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| 111 |
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| 112 | \fBpng_uint_32 png_get_image_width (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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| 113 |
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| 114 | \fBpng_int_32 png_get_int_32 (png_bytep \fIbuf\fP\fB);\fP
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| 115 |
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| 116 | \fBpng_byte png_get_interlace_type (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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| 117 |
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| 118 | \fBpng_uint_32 png_get_io_chunk_type (png_const_structp \fIpng_ptr\fP\fB);\fP
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| 119 |
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| 120 | \fBpng_voidp png_get_io_ptr (png_structp \fIpng_ptr\fP\fB);\fP
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| 121 |
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| 122 | \fBpng_uint_32 png_get_io_state (png_structp \fIpng_ptr\fP\fB);\fP
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| 123 |
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| 124 | \fBpng_byte png_get_libpng_ver (png_const_structp \fIpng_ptr\fP\fB);\fP
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| 125 |
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| 126 | \fBint png_get_palette_max(png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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| 127 |
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| 128 | \fBpng_voidp png_get_mem_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
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| 129 |
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| 130 | \fBpng_uint_32 png_get_oFFs (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*offset_x\fP\fB, png_uint_32 \fP\fI*offset_y\fP\fB, int \fI*unit_type\fP\fB);\fP
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| 131 |
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| 132 | \fBpng_uint_32 png_get_pCAL (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_charp \fP\fI*purpose\fP\fB, png_int_32 \fP\fI*X0\fP\fB, png_int_32 \fP\fI*X1\fP\fB, int \fP\fI*type\fP\fB, int \fP\fI*nparams\fP\fB, png_charp \fP\fI*units\fP\fB, png_charpp \fI*params\fP\fB);\fP
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| 133 |
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| 134 | \fBpng_uint_32 png_get_pHYs (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*res_x\fP\fB, png_uint_32 \fP\fI*res_y\fP\fB, int \fI*unit_type\fP\fB);\fP
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| 135 |
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| 136 | \fBfloat png_get_pixel_aspect_ratio (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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| 137 |
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| 138 | \fBpng_uint_32 png_get_pHYs_dpi (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*res_x\fP\fB, png_uint_32 \fP\fI*res_y\fP\fB, int \fI*unit_type\fP\fB);\fP
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| 139 |
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| 140 | \fBpng_fixed_point png_get_pixel_aspect_ratio_fixed (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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| 141 |
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| 142 | \fBpng_uint_32 png_get_pixels_per_inch (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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| 143 |
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| 144 | \fBpng_uint_32 png_get_pixels_per_meter (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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| 145 |
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| 146 | \fBpng_voidp png_get_progressive_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
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| 147 |
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| 148 | \fBpng_uint_32 png_get_PLTE (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_colorp \fP\fI*palette\fP\fB, int \fI*num_palette\fP\fB);\fP
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| 149 |
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| 150 | \fBpng_byte png_get_rgb_to_gray_status (png_const_structp \fIpng_ptr\fP\fB);\fP
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| 151 |
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| 152 | \fBpng_uint_32 png_get_rowbytes (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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| 153 |
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| 154 | \fBpng_bytepp png_get_rows (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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| 155 |
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| 156 | \fBpng_uint_32 png_get_sBIT (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_8p \fI*sig_bit\fP\fB);\fP
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| 157 |
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| 158 | \fBvoid png_get_sCAL (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, int* \fP\fIunit\fP\fB, double* \fP\fIwidth\fP\fB, double* \fIheight\fP\fB);\fP
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| 159 |
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| 160 | \fBvoid png_get_sCAL_fixed (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, int* \fP\fIunit\fP\fB, png_fixed_pointp \fP\fIwidth\fP\fB, png_fixed_pointp \fIheight\fP\fB);\fP
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| 161 |
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| 162 | \fBvoid png_get_sCAL_s (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, int* \fP\fIunit\fP\fB, png_charpp \fP\fIwidth\fP\fB, png_charpp \fIheight\fP\fB);\fP
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| 163 |
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| 164 | \fBpng_bytep png_get_signature (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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| 165 |
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| 166 | \fBpng_uint_32 png_get_sPLT (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_spalette_p \fI*splt_ptr\fP\fB);\fP
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| 167 |
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| 168 | \fBpng_uint_32 png_get_sRGB (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, int \fI*file_srgb_intent\fP\fB);\fP
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| 169 |
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| 170 | \fBpng_uint_32 png_get_text (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_textp \fP\fI*text_ptr\fP\fB, int \fI*num_text\fP\fB);\fP
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| 171 |
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| 172 | \fBpng_uint_32 png_get_tIME (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_timep \fI*mod_time\fP\fB);\fP
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| 173 |
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| 174 | \fBpng_uint_32 png_get_tRNS (png_const_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fI*trans_alpha\fP\fB, int \fP\fI*num_trans\fP\fB, png_color_16p \fI*trans_color\fP\fB);\fP
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| 175 |
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| 176 | \fB/* This function is really an inline macro. \fI*/
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| 177 |
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| 178 | \fBpng_uint_16 png_get_uint_16 (png_bytep \fIbuf\fP\fB);\fP
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| 179 |
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| 180 | \fBpng_uint_32 png_get_uint_31 (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIbuf\fP\fB);\fP
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| 181 |
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| 182 | \fB/* This function is really an inline macro. \fI*/
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| 183 |
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| 184 | \fBpng_uint_32 png_get_uint_32 (png_bytep \fIbuf\fP\fB);\fP
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| 185 |
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| 186 | \fBpng_uint_32 png_get_unknown_chunks (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_unknown_chunkpp \fIunknowns\fP\fB);\fP
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| 187 |
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| 188 | \fBpng_voidp png_get_user_chunk_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
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| 189 |
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| 190 | \fBpng_uint_32 png_get_user_height_max (png_const_structp \fIpng_ptr\fP\fB);\fP
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| 191 |
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| 192 | \fBpng_voidp png_get_user_transform_ptr (png_const_structp \fIpng_ptr\fP\fB);\fP
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| 193 |
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| 194 | \fBpng_uint_32 png_get_user_width_max (png_const_structp \fIpng_ptr\fP\fB);\fP
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| 195 |
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| 196 | \fBpng_uint_32 png_get_valid (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fIflag\fP\fB);\fP
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| 197 |
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| 198 | \fBfloat png_get_x_offset_inches (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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| 199 |
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| 200 | \fBpng_fixed_point png_get_x_offset_inches_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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| 201 |
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| 202 | \fBpng_int_32 png_get_x_offset_microns (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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| 203 |
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| 204 | \fBpng_int_32 png_get_x_offset_pixels (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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| 205 |
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| 206 | \fBpng_uint_32 png_get_x_pixels_per_inch (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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| 207 |
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| 208 | \fBpng_uint_32 png_get_x_pixels_per_meter (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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| 209 |
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| 210 | \fBfloat png_get_y_offset_inches (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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| 211 |
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| 212 | \fBpng_fixed_point png_get_y_offset_inches_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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| 213 |
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| 214 | \fBpng_int_32 png_get_y_offset_microns (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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| 215 |
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| 216 | \fBpng_int_32 png_get_y_offset_pixels (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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| 217 |
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| 218 | \fBpng_uint_32 png_get_y_pixels_per_inch (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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| 219 |
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| 220 | \fBpng_uint_32 png_get_y_pixels_per_meter (png_const_structp \fP\fIpng_ptr\fP\fB, png_const_infop \fIinfo_ptr\fP\fB);\fP
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| 221 |
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| 222 | \fBint png_handle_as_unknown (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIchunk_name\fP\fB);\fP
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| 223 |
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| 224 | \fBint png_image_begin_read_from_file (png_imagep \fP\fIimage\fP\fB, const char \fI*file_name\fP\fB);\fP
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| 225 |
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| 226 | \fBint png_image_begin_read_from_stdio (png_imagep \fP\fIimage\fP\fB, FILE* \fIfile\fP\fB);\fP
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| 227 |
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| 228 | \fBint, png_image_begin_read_from_memory (png_imagep \fP\fIimage\fP\fB, png_const_voidp \fP\fImemory\fP\fB, size_t \fIsize\fP\fB);\fP
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| 229 |
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| 230 | \fBint png_image_finish_read (png_imagep \fP\fIimage\fP\fB, png_colorp \fP\fIbackground\fP\fB, void \fP\fI*buffer\fP\fB, png_int_32 \fP\fIrow_stride\fP\fB, void \fI*colormap\fP\fB);\fP
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| 231 |
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| 232 | \fBvoid png_image_free (png_imagep \fIimage\fP\fB);\fP
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| 233 |
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| 234 | \fBint png_image_write_to_file (png_imagep \fP\fIimage\fP\fB, const char \fP\fI*file\fP\fB, int \fP\fIconvert_to_8bit\fP\fB, const void \fP\fI*buffer\fP\fB, png_int_32 \fP\fIrow_stride\fP\fB, void \fI*colormap\fP\fB);\fP
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| 235 |
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| 236 | \fBint png_image_write_to_memory (png_imagep \fP\fIimage\fP\fB, void \fP\fI*memory\fP\fB, png_alloc_size_t * PNG_RESTRICT \fP\fImemory_bytes\fP\fB, int \fP\fIconvert_to_8_bit\fP\fB, const void \fP\fI*buffer\fP\fB, png_int_32 \fP\fIrow_stride\fP\fB, const void \fI*colormap\fP\fB);\fP
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| 237 |
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| 238 | \fBint png_image_write_to_stdio (png_imagep \fP\fIimage\fP\fB, FILE \fP\fI*file\fP\fB, int \fP\fIconvert_to_8_bit\fP\fB, const void \fP\fI*buffer\fP\fB, png_int_32 \fP\fIrow_stride\fP\fB, void \fI*colormap\fP\fB);\fP
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| 239 |
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| 240 | \fBvoid png_info_init_3 (png_infopp \fP\fIinfo_ptr\fP\fB, size_t \fIpng_info_struct_size\fP\fB);\fP
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| 241 |
|
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| 242 | \fBvoid png_init_io (png_structp \fP\fIpng_ptr\fP\fB, FILE \fI*fp\fP\fB);\fP
|
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| 243 |
|
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| 244 | \fBvoid png_longjmp (png_structp \fP\fIpng_ptr\fP\fB, int \fIval\fP\fB);\fP
|
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| 245 |
|
|---|
| 246 | \fBpng_voidp png_malloc (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
|
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| 247 |
|
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| 248 | \fBpng_voidp png_malloc_default (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
|
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| 249 |
|
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| 250 | \fBpng_voidp png_malloc_warn (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIsize\fP\fB);\fP
|
|---|
| 251 |
|
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| 252 | \fBpng_uint_32 png_permit_mng_features (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fImng_features_permitted\fP\fB);\fP
|
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| 253 |
|
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| 254 | \fBvoid png_process_data (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fIbuffer\fP\fB, size_t \fIbuffer_size\fP\fB);\fP
|
|---|
| 255 |
|
|---|
| 256 | \fBsize_t png_process_data_pause (png_structp \fP\fIpng_ptr\fP\fB, int \fIsave\fP\fB);\fP
|
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| 257 |
|
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| 258 | \fBpng_uint_32 png_process_data_skip (png_structp \fP\fIpng_ptr\fP\fB);\fP
|
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| 259 |
|
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| 260 | \fBvoid png_progressive_combine_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIold_row\fP\fB, png_bytep \fInew_row\fP\fB);\fP
|
|---|
| 261 |
|
|---|
| 262 | \fBvoid png_read_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
|
|---|
| 263 |
|
|---|
| 264 | \fBvoid png_read_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
|
|---|
| 265 |
|
|---|
| 266 | \fBvoid png_read_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
|
|---|
| 267 |
|
|---|
| 268 | \fBvoid png_read_png (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fItransforms\fP\fB, png_voidp \fIparams\fP\fB);\fP
|
|---|
| 269 |
|
|---|
| 270 | \fBvoid png_read_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIrow\fP\fB, png_bytep \fIdisplay_row\fP\fB);\fP
|
|---|
| 271 |
|
|---|
| 272 | \fBvoid png_read_rows (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fP\fIrow\fP\fB, png_bytepp \fP\fIdisplay_row\fP\fB, png_uint_32 \fInum_rows\fP\fB);\fP
|
|---|
| 273 |
|
|---|
| 274 | \fBvoid png_read_update_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
|
|---|
| 275 |
|
|---|
| 276 | \fBint png_reset_zstream (png_structp \fIpng_ptr\fP\fB);\fP
|
|---|
| 277 |
|
|---|
| 278 | \fBvoid png_save_int_32 (png_bytep \fP\fIbuf\fP\fB, png_int_32 \fIi\fP\fB);\fP
|
|---|
| 279 |
|
|---|
| 280 | \fBvoid png_save_uint_16 (png_bytep \fP\fIbuf\fP\fB, unsigned int \fIi\fP\fB);\fP
|
|---|
| 281 |
|
|---|
| 282 | \fBvoid png_save_uint_32 (png_bytep \fP\fIbuf\fP\fB, png_uint_32 \fIi\fP\fB);\fP
|
|---|
| 283 |
|
|---|
| 284 | \fBvoid png_set_add_alpha (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
|
|---|
| 285 |
|
|---|
| 286 | \fBvoid png_set_alpha_mode (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImode\fP\fB, double \fIoutput_gamma\fP\fB);\fP
|
|---|
| 287 |
|
|---|
| 288 | \fBvoid png_set_alpha_mode_fixed (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImode\fP\fB, png_fixed_point \fIoutput_gamma\fP\fB);\fP
|
|---|
| 289 |
|
|---|
| 290 | \fBvoid png_set_background (png_structp \fP\fIpng_ptr\fP\fB, png_color_16p \fP\fIbackground_color\fP\fB, int \fP\fIbackground_gamma_code\fP\fB, int \fP\fIneed_expand\fP\fB, double \fIbackground_gamma\fP\fB);\fP
|
|---|
| 291 |
|
|---|
| 292 | \fBvoid png_set_background_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_color_16p \fP\fIbackground_color\fP\fB, int \fP\fIbackground_gamma_code\fP\fB, int \fP\fIneed_expand\fP\fB, png_uint_32 \fIbackground_gamma\fP\fB);\fP
|
|---|
| 293 |
|
|---|
| 294 | \fBvoid png_set_benign_errors (png_structp \fP\fIpng_ptr\fP\fB, int \fIallowed\fP\fB);\fP
|
|---|
| 295 |
|
|---|
| 296 | \fBvoid png_set_bgr (png_structp \fIpng_ptr\fP\fB);\fP
|
|---|
| 297 |
|
|---|
| 298 | \fBvoid png_set_bKGD (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_16p \fIbackground\fP\fB);\fP
|
|---|
| 299 |
|
|---|
| 300 | \fBvoid png_set_check_for_invalid_index (png_structrp \fP\fIpng_ptr\fP\fB, int \fIallowed\fP\fB);\fP
|
|---|
| 301 |
|
|---|
| 302 | \fBvoid png_set_cHRM (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fP\fIwhite_x\fP\fB, double \fP\fIwhite_y\fP\fB, double \fP\fIred_x\fP\fB, double \fP\fIred_y\fP\fB, double \fP\fIgreen_x\fP\fB, double \fP\fIgreen_y\fP\fB, double \fP\fIblue_x\fP\fB, double \fIblue_y\fP\fB);\fP
|
|---|
| 303 |
|
|---|
| 304 | \fBvoid png_set_cHRM_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIwhite_x\fP\fB, png_uint_32 \fP\fIwhite_y\fP\fB, png_uint_32 \fP\fIred_x\fP\fB, png_uint_32 \fP\fIred_y\fP\fB, png_uint_32 \fP\fIgreen_x\fP\fB, png_uint_32 \fP\fIgreen_y\fP\fB, png_uint_32 \fP\fIblue_x\fP\fB, png_uint_32 \fIblue_y\fP\fB);\fP
|
|---|
| 305 |
|
|---|
| 306 | \fBvoid png_set_cHRM_XYZ (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fP\fIred_X\fP\fB, double \fP\fIred_Y\fP\fB, double \fP\fIred_Z\fP\fB, double \fP\fIgreen_X\fP\fB, double \fP\fIgreen_Y\fP\fB, double \fP\fIgreen_Z\fP\fB, double \fP\fIblue_X\fP\fB, double \fP\fIblue_Y\fP\fB, double \fIblue_Z\fP\fB);\fP
|
|---|
| 307 |
|
|---|
| 308 | \fBvoid png_set_cHRM_XYZ_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_fixed_point \fP\fIint_red_X\fP\fB, png_fixed_point \fP\fIint_red_Y\fP\fB, png_fixed_point \fP\fIint_red_Z\fP\fB, png_fixed_point \fP\fIint_green_X\fP\fB, png_fixed_point \fP\fIint_green_Y\fP\fB, png_fixed_point \fP\fIint_green_Z\fP\fB, png_fixed_point \fP\fIint_blue_X\fP\fB, png_fixed_point \fP\fIint_blue_Y\fP\fB, png_fixed_point \fIint_blue_Z\fP\fB);\fP
|
|---|
| 309 |
|
|---|
| 310 | \fBvoid png_set_chunk_cache_max (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIuser_chunk_cache_max\fP\fB);\fP
|
|---|
| 311 |
|
|---|
| 312 | \fBvoid png_set_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP
|
|---|
| 313 |
|
|---|
| 314 | \fBvoid png_set_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP
|
|---|
| 315 |
|
|---|
| 316 | \fBvoid png_set_compression_method (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod\fP\fB);\fP
|
|---|
| 317 |
|
|---|
| 318 | \fBvoid png_set_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP
|
|---|
| 319 |
|
|---|
| 320 | \fBvoid png_set_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP
|
|---|
| 321 |
|
|---|
| 322 | \fBvoid png_set_crc_action (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIcrit_action\fP\fB, int \fIancil_action\fP\fB);\fP
|
|---|
| 323 |
|
|---|
| 324 | \fBvoid png_set_error_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fIwarning_fn\fP\fB);\fP
|
|---|
| 325 |
|
|---|
| 326 | \fBvoid png_set_expand (png_structp \fIpng_ptr\fP\fB);\fP
|
|---|
| 327 |
|
|---|
| 328 | \fBvoid png_set_expand_16 (png_structp \fIpng_ptr\fP\fB);\fP
|
|---|
| 329 |
|
|---|
| 330 | \fBvoid png_set_expand_gray_1_2_4_to_8 (png_structp \fIpng_ptr\fP\fB);\fP
|
|---|
| 331 |
|
|---|
| 332 | \fBvoid png_set_filler (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
|
|---|
| 333 |
|
|---|
| 334 | \fBvoid png_set_filter (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImethod\fP\fB, int \fIfilters\fP\fB);\fP
|
|---|
| 335 |
|
|---|
| 336 | \fBvoid png_set_filter_heuristics (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIheuristic_method\fP\fB, int \fP\fInum_weights\fP\fB, png_doublep \fP\fIfilter_weights\fP\fB, png_doublep \fIfilter_costs\fP\fB);\fP
|
|---|
| 337 |
|
|---|
| 338 | \fBvoid png_set_filter_heuristics_fixed (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIheuristic_method\fP\fB, int \fP\fInum_weights\fP\fB, png_fixed_point_p \fP\fIfilter_weights\fP\fB, png_fixed_point_p \fIfilter_costs\fP\fB);\fP
|
|---|
| 339 |
|
|---|
| 340 | \fBvoid png_set_flush (png_structp \fP\fIpng_ptr\fP\fB, int \fInrows\fP\fB);\fP
|
|---|
| 341 |
|
|---|
| 342 | \fBvoid png_set_gamma (png_structp \fP\fIpng_ptr\fP\fB, double \fP\fIscreen_gamma\fP\fB, double \fIdefault_file_gamma\fP\fB);\fP
|
|---|
| 343 |
|
|---|
| 344 | \fBvoid png_set_gamma_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIscreen_gamma\fP\fB, png_uint_32 \fIdefault_file_gamma\fP\fB);\fP
|
|---|
| 345 |
|
|---|
| 346 | \fBvoid png_set_gAMA (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fIfile_gamma\fP\fB);\fP
|
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| 347 |
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| 348 | \fBvoid png_set_gAMA_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fIfile_gamma\fP\fB);\fP
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| 349 |
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| 350 | \fBvoid png_set_gray_1_2_4_to_8 (png_structp \fIpng_ptr\fP\fB);\fP
|
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| 351 |
|
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| 352 | \fBvoid png_set_gray_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
|
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| 353 |
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| 354 | \fBvoid png_set_eXIf (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fIexif\fP\fB);\fP
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| 355 |
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| 356 | \fBvoid png_set_eXIf_1 (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fInum_exif\fP\fB, png_bytep \fIexif\fP\fB);\fP
|
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| 357 |
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| 358 | \fBvoid png_set_hIST (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_16p \fIhist\fP\fB);\fP
|
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| 359 |
|
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| 360 | \fBvoid png_set_iCCP (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_const_charp \fP\fIname\fP\fB, int \fP\fIcompression_type\fP\fB, png_const_bytep \fP\fIprofile\fP\fB, png_uint_32 \fIproflen\fP\fB);\fP
|
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| 361 |
|
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| 362 | \fBint png_set_interlace_handling (png_structp \fIpng_ptr\fP\fB);\fP
|
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| 363 |
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| 364 | \fBvoid png_set_invalid (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fImask\fP\fB);\fP
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| 365 |
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| 366 | \fBvoid png_set_invert_alpha (png_structp \fIpng_ptr\fP\fB);\fP
|
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| 367 |
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| 368 | \fBvoid png_set_invert_mono (png_structp \fIpng_ptr\fP\fB);\fP
|
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| 369 |
|
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| 370 | \fBvoid png_set_IHDR (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIwidth\fP\fB, png_uint_32 \fP\fIheight\fP\fB, int \fP\fIbit_depth\fP\fB, int \fP\fIcolor_type\fP\fB, int \fP\fIinterlace_type\fP\fB, int \fP\fIcompression_type\fP\fB, int \fIfilter_type\fP\fB);\fP
|
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| 371 |
|
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| 372 | \fBvoid png_set_keep_unknown_chunks (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIkeep\fP\fB, png_bytep \fP\fIchunk_list\fP\fB, int \fInum_chunks\fP\fB);\fP
|
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| 373 |
|
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| 374 | \fBjmp_buf* png_set_longjmp_fn (png_structp \fP\fIpng_ptr\fP\fB, png_longjmp_ptr \fP\fIlongjmp_fn\fP\fB, size_t \fIjmp_buf_size\fP\fB);\fP
|
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| 375 |
|
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| 376 | \fBvoid png_set_chunk_malloc_max (png_structp \fP\fIpng_ptr\fP\fB, png_alloc_size_t \fIuser_chunk_cache_max\fP\fB);\fP
|
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| 377 |
|
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| 378 | \fBvoid png_set_compression_buffer_size (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
|
|---|
| 379 |
|
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| 380 | \fBvoid png_set_mem_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fImem_ptr\fP\fB, png_malloc_ptr \fP\fImalloc_fn\fP\fB, png_free_ptr \fIfree_fn\fP\fB);\fP
|
|---|
| 381 |
|
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| 382 | \fBvoid png_set_oFFs (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIoffset_x\fP\fB, png_uint_32 \fP\fIoffset_y\fP\fB, int \fIunit_type\fP\fB);\fP
|
|---|
| 383 |
|
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| 384 | \fBint png_set_option(png_structrp \fP\fIpng_ptr\fP\fB, int \fP\fIoption\fP\fB, int \fIonoff\fP\fB);\fP
|
|---|
| 385 |
|
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| 386 | \fBvoid png_set_packing (png_structp \fIpng_ptr\fP\fB);\fP
|
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| 387 |
|
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| 388 | \fBvoid png_set_packswap (png_structp \fIpng_ptr\fP\fB);\fP
|
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| 389 |
|
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| 390 | \fBvoid png_set_palette_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
|
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| 391 |
|
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| 392 | \fBvoid png_set_pCAL (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charp \fP\fIpurpose\fP\fB, png_int_32 \fP\fIX0\fP\fB, png_int_32 \fP\fIX1\fP\fB, int \fP\fItype\fP\fB, int \fP\fInparams\fP\fB, png_charp \fP\fIunits\fP\fB, png_charpp \fIparams\fP\fB);\fP
|
|---|
| 393 |
|
|---|
| 394 | \fBvoid png_set_pHYs (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIres_x\fP\fB, png_uint_32 \fP\fIres_y\fP\fB, int \fIunit_type\fP\fB);\fP
|
|---|
| 395 |
|
|---|
| 396 | \fBvoid png_set_progressive_read_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIprogressive_ptr\fP\fB, png_progressive_info_ptr \fP\fIinfo_fn\fP\fB, png_progressive_row_ptr \fP\fIrow_fn\fP\fB, png_progressive_end_ptr \fIend_fn\fP\fB);\fP
|
|---|
| 397 |
|
|---|
| 398 | \fBvoid png_set_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_colorp \fP\fIpalette\fP\fB, int \fInum_palette\fP\fB);\fP
|
|---|
| 399 |
|
|---|
| 400 | \fBvoid png_set_quantize (png_structp \fP\fIpng_ptr\fP\fB, png_colorp \fP\fIpalette\fP\fB, int \fP\fInum_palette\fP\fB, int \fP\fImaximum_colors\fP\fB, png_uint_16p \fP\fIhistogram\fP\fB, int \fIfull_quantize\fP\fB);\fP
|
|---|
| 401 |
|
|---|
| 402 | \fBvoid png_set_read_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIio_ptr\fP\fB, png_rw_ptr \fIread_data_fn\fP\fB);\fP
|
|---|
| 403 |
|
|---|
| 404 | \fBvoid png_set_read_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_read_status_ptr \fIread_row_fn\fP\fB);\fP
|
|---|
| 405 |
|
|---|
| 406 | \fBvoid png_set_read_user_chunk_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIuser_chunk_ptr\fP\fB, png_user_chunk_ptr \fIread_user_chunk_fn\fP\fB);\fP
|
|---|
| 407 |
|
|---|
| 408 | \fBvoid png_set_read_user_transform_fn (png_structp \fP\fIpng_ptr\fP\fB, png_user_transform_ptr \fIread_user_transform_fn\fP\fB);\fP
|
|---|
| 409 |
|
|---|
| 410 | \fBvoid png_set_rgb_to_gray (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIerror_action\fP\fB, double \fP\fIred\fP\fB, double \fIgreen\fP\fB);\fP
|
|---|
| 411 |
|
|---|
| 412 | \fBvoid png_set_rgb_to_gray_fixed (png_structp \fP\fIpng_ptr\fP\fB, int error_action png_uint_32 \fP\fIred\fP\fB, png_uint_32 \fIgreen\fP\fB);\fP
|
|---|
| 413 |
|
|---|
| 414 | \fBvoid png_set_rows (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytepp \fIrow_pointers\fP\fB);\fP
|
|---|
| 415 |
|
|---|
| 416 | \fBvoid png_set_sBIT (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_8p \fIsig_bit\fP\fB);\fP
|
|---|
| 417 |
|
|---|
| 418 | \fBvoid png_set_sCAL (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIunit\fP\fB, double \fP\fIwidth\fP\fB, double \fIheight\fP\fB);\fP
|
|---|
| 419 |
|
|---|
| 420 | \fBvoid png_set_sCAL_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIunit\fP\fB, png_fixed_point \fP\fIwidth\fP\fB, png_fixed_point \fIheight\fP\fB);\fP
|
|---|
| 421 |
|
|---|
| 422 | \fBvoid png_set_sCAL_s (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIunit\fP\fB, png_charp \fP\fIwidth\fP\fB, png_charp \fIheight\fP\fB);\fP
|
|---|
| 423 |
|
|---|
| 424 | \fBvoid png_set_scale_16 (png_structp \fIpng_ptr\fP\fB);\fP
|
|---|
| 425 |
|
|---|
| 426 | \fBvoid png_set_shift (png_structp \fP\fIpng_ptr\fP\fB, png_color_8p \fItrue_bits\fP\fB);\fP
|
|---|
| 427 |
|
|---|
| 428 | \fBvoid png_set_sig_bytes (png_structp \fP\fIpng_ptr\fP\fB, int \fInum_bytes\fP\fB);\fP
|
|---|
| 429 |
|
|---|
| 430 | \fBvoid png_set_sPLT (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_spalette_p \fP\fIsplt_ptr\fP\fB, int \fInum_spalettes\fP\fB);\fP
|
|---|
| 431 |
|
|---|
| 432 | \fBvoid png_set_sRGB (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIsrgb_intent\fP\fB);\fP
|
|---|
| 433 |
|
|---|
| 434 | \fBvoid png_set_sRGB_gAMA_and_cHRM (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIsrgb_intent\fP\fB);\fP
|
|---|
| 435 |
|
|---|
| 436 | \fBvoid png_set_strip_16 (png_structp \fIpng_ptr\fP\fB);\fP
|
|---|
| 437 |
|
|---|
| 438 | \fBvoid png_set_strip_alpha (png_structp \fIpng_ptr\fP\fB);\fP
|
|---|
| 439 |
|
|---|
| 440 | \fBvoid png_set_strip_error_numbers (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIstrip_mode\fP\fB);\fP
|
|---|
| 441 |
|
|---|
| 442 | \fBvoid png_set_swap (png_structp \fIpng_ptr\fP\fB);\fP
|
|---|
| 443 |
|
|---|
| 444 | \fBvoid png_set_swap_alpha (png_structp \fIpng_ptr\fP\fB);\fP
|
|---|
| 445 |
|
|---|
| 446 | \fBvoid png_set_text (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_textp \fP\fItext_ptr\fP\fB, int \fInum_text\fP\fB);\fP
|
|---|
| 447 |
|
|---|
| 448 | \fBvoid png_set_text_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP
|
|---|
| 449 |
|
|---|
| 450 | \fBvoid png_set_text_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP
|
|---|
| 451 |
|
|---|
| 452 | \fBvoid png_set_text_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP
|
|---|
| 453 |
|
|---|
| 454 | \fBvoid png_set_text_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP
|
|---|
| 455 |
|
|---|
| 456 | \fBvoid png_set_text_compression_method (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod\fP\fB);\fP
|
|---|
| 457 |
|
|---|
| 458 | \fBvoid png_set_tIME (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_timep \fImod_time\fP\fB);\fP
|
|---|
| 459 |
|
|---|
| 460 | \fBvoid png_set_tRNS (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fItrans_alpha\fP\fB, int \fP\fInum_trans\fP\fB, png_color_16p \fItrans_color\fP\fB);\fP
|
|---|
| 461 |
|
|---|
| 462 | \fBvoid png_set_tRNS_to_alpha (png_structp \fIpng_ptr\fP\fB);\fP
|
|---|
| 463 |
|
|---|
| 464 | \fBpng_uint_32 png_set_unknown_chunks (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_unknown_chunkp \fP\fIunknowns\fP\fB, int \fP\fInum\fP\fB, int \fIlocation\fP\fB);\fP
|
|---|
| 465 |
|
|---|
| 466 | \fBvoid png_set_unknown_chunk_location (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIchunk\fP\fB, int \fIlocation\fP\fB);\fP
|
|---|
| 467 |
|
|---|
| 468 | \fBvoid png_set_user_limits (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIuser_width_max\fP\fB, png_uint_32 \fIuser_height_max\fP\fB);\fP
|
|---|
| 469 |
|
|---|
| 470 | \fBvoid png_set_user_transform_info (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIuser_transform_ptr\fP\fB, int \fP\fIuser_transform_depth\fP\fB, int \fIuser_transform_channels\fP\fB);\fP
|
|---|
| 471 |
|
|---|
| 472 | \fBvoid png_set_write_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIio_ptr\fP\fB, png_rw_ptr \fP\fIwrite_data_fn\fP\fB, png_flush_ptr \fIoutput_flush_fn\fP\fB);\fP
|
|---|
| 473 |
|
|---|
| 474 | \fBvoid png_set_write_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_write_status_ptr \fIwrite_row_fn\fP\fB);\fP
|
|---|
| 475 |
|
|---|
| 476 | \fBvoid png_set_write_user_transform_fn (png_structp \fP\fIpng_ptr\fP\fB, png_user_transform_ptr \fIwrite_user_transform_fn\fP\fB);\fP
|
|---|
| 477 |
|
|---|
| 478 | \fBint png_sig_cmp (png_bytep \fP\fIsig\fP\fB, size_t \fP\fIstart\fP\fB, size_t \fInum_to_check\fP\fB);\fP
|
|---|
| 479 |
|
|---|
| 480 | \fBvoid png_start_read_image (png_structp \fIpng_ptr\fP\fB);\fP
|
|---|
| 481 |
|
|---|
| 482 | \fBvoid png_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
|
|---|
| 483 |
|
|---|
| 484 | \fBvoid png_write_chunk (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIchunk_name\fP\fB, png_bytep \fP\fIdata\fP\fB, size_t \fIlength\fP\fB);\fP
|
|---|
| 485 |
|
|---|
| 486 | \fBvoid png_write_chunk_data (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIdata\fP\fB, size_t \fIlength\fP\fB);\fP
|
|---|
| 487 |
|
|---|
| 488 | \fBvoid png_write_chunk_end (png_structp \fIpng_ptr\fP\fB);\fP
|
|---|
| 489 |
|
|---|
| 490 | \fBvoid png_write_chunk_start (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIchunk_name\fP\fB, png_uint_32 \fIlength\fP\fB);\fP
|
|---|
| 491 |
|
|---|
| 492 | \fBvoid png_write_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
|
|---|
| 493 |
|
|---|
| 494 | \fBvoid png_write_flush (png_structp \fIpng_ptr\fP\fB);\fP
|
|---|
| 495 |
|
|---|
| 496 | \fBvoid png_write_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
|
|---|
| 497 |
|
|---|
| 498 | \fBvoid png_write_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
|
|---|
| 499 |
|
|---|
| 500 | \fBvoid png_write_info_before_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
|
|---|
| 501 |
|
|---|
| 502 | \fBvoid png_write_png (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fItransforms\fP\fB, png_voidp \fIparams\fP\fB);\fP
|
|---|
| 503 |
|
|---|
| 504 | \fBvoid png_write_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIrow\fP\fB);\fP
|
|---|
| 505 |
|
|---|
| 506 | \fBvoid png_write_rows (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fP\fIrow\fP\fB, png_uint_32 \fInum_rows\fP\fB);\fP
|
|---|
| 507 |
|
|---|
| 508 | \fBvoid png_write_sig (png_structp \fIpng_ptr\fP\fB);\fP
|
|---|
| 509 |
|
|---|
| 510 | .SH DESCRIPTION
|
|---|
| 511 | The
|
|---|
| 512 | .I libpng
|
|---|
| 513 | library supports encoding, decoding, and various manipulations of
|
|---|
| 514 | the Portable Network Graphics (PNG) format image files. It uses the
|
|---|
| 515 | .IR zlib(3)
|
|---|
| 516 | compression library.
|
|---|
| 517 | Following is a copy of the libpng-manual.txt file that accompanies libpng.
|
|---|
| 518 |
|
|---|
| 519 | .SH LIBPNG.TXT
|
|---|
| 520 | libpng-manual.txt - A description on how to use and modify libpng
|
|---|
| 521 |
|
|---|
| 522 | Copyright (c) 2018-2019 Cosmin Truta
|
|---|
| 523 | Copyright (c) 1998-2018 Glenn Randers-Pehrson
|
|---|
| 524 |
|
|---|
| 525 | This document is released under the libpng license.
|
|---|
| 526 | For conditions of distribution and use, see the disclaimer
|
|---|
| 527 | and license in png.h
|
|---|
| 528 |
|
|---|
| 529 | Based on:
|
|---|
| 530 |
|
|---|
| 531 | libpng version 1.6.36, December 2018, through 1.6.37 - April 2019
|
|---|
| 532 | Updated and distributed by Cosmin Truta
|
|---|
| 533 | Copyright (c) 2018-2019 Cosmin Truta
|
|---|
| 534 |
|
|---|
| 535 | libpng versions 0.97, January 1998, through 1.6.35 - July 2018
|
|---|
| 536 | Updated and distributed by Glenn Randers-Pehrson
|
|---|
| 537 | Copyright (c) 1998-2018 Glenn Randers-Pehrson
|
|---|
| 538 |
|
|---|
| 539 | libpng 1.0 beta 6 - version 0.96 - May 28, 1997
|
|---|
| 540 | Updated and distributed by Andreas Dilger
|
|---|
| 541 | Copyright (c) 1996, 1997 Andreas Dilger
|
|---|
| 542 |
|
|---|
| 543 | libpng 1.0 beta 2 - version 0.88 - January 26, 1996
|
|---|
| 544 | For conditions of distribution and use, see copyright
|
|---|
| 545 | notice in png.h. Copyright (c) 1995, 1996 Guy Eric
|
|---|
| 546 | Schalnat, Group 42, Inc.
|
|---|
| 547 |
|
|---|
| 548 | Updated/rewritten per request in the libpng FAQ
|
|---|
| 549 | Copyright (c) 1995, 1996 Frank J. T. Wojcik
|
|---|
| 550 | December 18, 1995 & January 20, 1996
|
|---|
| 551 |
|
|---|
| 552 | TABLE OF CONTENTS
|
|---|
| 553 |
|
|---|
| 554 | I. Introduction
|
|---|
| 555 | II. Structures
|
|---|
| 556 | III. Reading
|
|---|
| 557 | IV. Writing
|
|---|
| 558 | V. Simplified API
|
|---|
| 559 | VI. Modifying/Customizing libpng
|
|---|
| 560 | VII. MNG support
|
|---|
| 561 | VIII. Changes to Libpng from version 0.88
|
|---|
| 562 | IX. Changes to Libpng from version 1.0.x to 1.2.x
|
|---|
| 563 | X. Changes to Libpng from version 1.0.x/1.2.x to 1.4.x
|
|---|
| 564 | XI. Changes to Libpng from version 1.4.x to 1.5.x
|
|---|
| 565 | XII. Changes to Libpng from version 1.5.x to 1.6.x
|
|---|
| 566 | XIII. Detecting libpng
|
|---|
| 567 | XIV. Source code repository
|
|---|
| 568 | XV. Coding style
|
|---|
| 569 |
|
|---|
| 570 | .SH I. Introduction
|
|---|
| 571 |
|
|---|
| 572 | This file describes how to use and modify the PNG reference library
|
|---|
| 573 | (known as libpng) for your own use. In addition to this
|
|---|
| 574 | file, example.c is a good starting point for using the library, as
|
|---|
| 575 | it is heavily commented and should include everything most people
|
|---|
| 576 | will need. We assume that libpng is already installed; see the
|
|---|
| 577 | INSTALL file for instructions on how to configure and install libpng.
|
|---|
| 578 |
|
|---|
| 579 | For examples of libpng usage, see the files "example.c", "pngtest.c",
|
|---|
| 580 | and the files in the "contrib" directory, all of which are included in
|
|---|
| 581 | the libpng distribution.
|
|---|
| 582 |
|
|---|
| 583 | Libpng was written as a companion to the PNG specification, as a way
|
|---|
| 584 | of reducing the amount of time and effort it takes to support the PNG
|
|---|
| 585 | file format in application programs.
|
|---|
| 586 |
|
|---|
| 587 | The PNG specification (second edition), November 2003, is available as
|
|---|
| 588 | a W3C Recommendation and as an ISO Standard (ISO/IEC 15948:2004 (E)) at
|
|---|
| 589 | <https://www.w3.org/TR/2003/REC-PNG-20031110/>.
|
|---|
| 590 | The W3C and ISO documents have identical technical content.
|
|---|
| 591 |
|
|---|
| 592 | The PNG-1.2 specification is available at
|
|---|
| 593 | <https://png-mng.sourceforge.io/pub/png/spec/1.2/>.
|
|---|
| 594 | It is technically equivalent
|
|---|
| 595 | to the PNG specification (second edition) but has some additional material.
|
|---|
| 596 |
|
|---|
| 597 | The PNG-1.0 specification is available as RFC 2083 at
|
|---|
| 598 | <https://png-mng.sourceforge.io/pub/png/spec/1.0/> and as a
|
|---|
| 599 | W3C Recommendation at <https://www.w3.org/TR/REC-png-961001>.
|
|---|
| 600 |
|
|---|
| 601 | Some additional chunks are described in the special-purpose public chunks
|
|---|
| 602 | documents at <http://www.libpng.org/pub/png/spec/register/>
|
|---|
| 603 |
|
|---|
| 604 | Other information
|
|---|
| 605 | about PNG, and the latest version of libpng, can be found at the PNG home
|
|---|
| 606 | page, <http://www.libpng.org/pub/png/>.
|
|---|
| 607 |
|
|---|
| 608 | Most users will not have to modify the library significantly; advanced
|
|---|
| 609 | users may want to modify it more. All attempts were made to make it as
|
|---|
| 610 | complete as possible, while keeping the code easy to understand.
|
|---|
| 611 | Currently, this library only supports C. Support for other languages
|
|---|
| 612 | is being considered.
|
|---|
| 613 |
|
|---|
| 614 | Libpng has been designed to handle multiple sessions at one time,
|
|---|
| 615 | to be easily modifiable, to be portable to the vast majority of
|
|---|
| 616 | machines (ANSI, K&R, 16-, 32-, and 64-bit) available, and to be easy
|
|---|
| 617 | to use. The ultimate goal of libpng is to promote the acceptance of
|
|---|
| 618 | the PNG file format in whatever way possible. While there is still
|
|---|
| 619 | work to be done (see the TODO file), libpng should cover the
|
|---|
| 620 | majority of the needs of its users.
|
|---|
| 621 |
|
|---|
| 622 | Libpng uses zlib for its compression and decompression of PNG files.
|
|---|
| 623 | Further information about zlib, and the latest version of zlib, can
|
|---|
| 624 | be found at the zlib home page, <https://zlib.net/>.
|
|---|
| 625 | The zlib compression utility is a general purpose utility that is
|
|---|
| 626 | useful for more than PNG files, and can be used without libpng.
|
|---|
| 627 | See the documentation delivered with zlib for more details.
|
|---|
| 628 | You can usually find the source files for the zlib utility wherever you
|
|---|
| 629 | find the libpng source files.
|
|---|
| 630 |
|
|---|
| 631 | Libpng is thread safe, provided the threads are using different
|
|---|
| 632 | instances of the structures. Each thread should have its own
|
|---|
| 633 | png_struct and png_info instances, and thus its own image.
|
|---|
| 634 | Libpng does not protect itself against two threads using the
|
|---|
| 635 | same instance of a structure.
|
|---|
| 636 |
|
|---|
| 637 | .SH II. Structures
|
|---|
| 638 |
|
|---|
| 639 | There are two main structures that are important to libpng, png_struct
|
|---|
| 640 | and png_info. Both are internal structures that are no longer exposed
|
|---|
| 641 | in the libpng interface (as of libpng 1.5.0).
|
|---|
| 642 |
|
|---|
| 643 | The png_info structure is designed to provide information about the
|
|---|
| 644 | PNG file. At one time, the fields of png_info were intended to be
|
|---|
| 645 | directly accessible to the user. However, this tended to cause problems
|
|---|
| 646 | with applications using dynamically loaded libraries, and as a result
|
|---|
| 647 | a set of interface functions for png_info (the png_get_*() and png_set_*()
|
|---|
| 648 | functions) was developed, and direct access to the png_info fields was
|
|---|
| 649 | deprecated..
|
|---|
| 650 |
|
|---|
| 651 | The png_struct structure is the object used by the library to decode a
|
|---|
| 652 | single image. As of 1.5.0 this structure is also not exposed.
|
|---|
| 653 |
|
|---|
| 654 | Almost all libpng APIs require a pointer to a png_struct as the first argument.
|
|---|
| 655 | Many (in particular the png_set and png_get APIs) also require a pointer
|
|---|
| 656 | to png_info as the second argument. Some application visible macros
|
|---|
| 657 | defined in png.h designed for basic data access (reading and writing
|
|---|
| 658 | integers in the PNG format) don't take a png_info pointer, but it's almost
|
|---|
| 659 | always safe to assume that a (png_struct*) has to be passed to call an API
|
|---|
| 660 | function.
|
|---|
| 661 |
|
|---|
| 662 | You can have more than one png_info structure associated with an image,
|
|---|
| 663 | as illustrated in pngtest.c, one for information valid prior to the
|
|---|
| 664 | IDAT chunks and another (called "end_info" below) for things after them.
|
|---|
| 665 |
|
|---|
| 666 | The png.h header file is an invaluable reference for programming with libpng.
|
|---|
| 667 | And while I'm on the topic, make sure you include the libpng header file:
|
|---|
| 668 |
|
|---|
| 669 | #include <png.h>
|
|---|
| 670 |
|
|---|
| 671 | and also (as of libpng-1.5.0) the zlib header file, if you need it:
|
|---|
| 672 |
|
|---|
| 673 | #include <zlib.h>
|
|---|
| 674 |
|
|---|
| 675 | .SS Types
|
|---|
| 676 |
|
|---|
| 677 | The png.h header file defines a number of integral types used by the
|
|---|
| 678 | APIs. Most of these are fairly obvious; for example types corresponding
|
|---|
| 679 | to integers of particular sizes and types for passing color values.
|
|---|
| 680 |
|
|---|
| 681 | One exception is how non-integral numbers are handled. For application
|
|---|
| 682 | convenience most APIs that take such numbers have C (double) arguments;
|
|---|
| 683 | however, internally PNG, and libpng, use 32 bit signed integers and encode
|
|---|
| 684 | the value by multiplying by 100,000. As of libpng 1.5.0 a convenience
|
|---|
| 685 | macro PNG_FP_1 is defined in png.h along with a type (png_fixed_point)
|
|---|
| 686 | which is simply (png_int_32).
|
|---|
| 687 |
|
|---|
| 688 | All APIs that take (double) arguments also have a matching API that
|
|---|
| 689 | takes the corresponding fixed point integer arguments. The fixed point
|
|---|
| 690 | API has the same name as the floating point one with "_fixed" appended.
|
|---|
| 691 | The actual range of values permitted in the APIs is frequently less than
|
|---|
| 692 | the full range of (png_fixed_point) (\-21474 to +21474). When APIs require
|
|---|
| 693 | a non-negative argument the type is recorded as png_uint_32 above. Consult
|
|---|
| 694 | the header file and the text below for more information.
|
|---|
| 695 |
|
|---|
| 696 | Special care must be take with sCAL chunk handling because the chunk itself
|
|---|
| 697 | uses non-integral values encoded as strings containing decimal floating point
|
|---|
| 698 | numbers. See the comments in the header file.
|
|---|
| 699 |
|
|---|
| 700 | .SS Configuration
|
|---|
| 701 |
|
|---|
| 702 | The main header file function declarations are frequently protected by C
|
|---|
| 703 | preprocessing directives of the form:
|
|---|
| 704 |
|
|---|
| 705 | #ifdef PNG_feature_SUPPORTED
|
|---|
| 706 | declare-function
|
|---|
| 707 | #endif
|
|---|
| 708 | ...
|
|---|
| 709 | #ifdef PNG_feature_SUPPORTED
|
|---|
| 710 | use-function
|
|---|
| 711 | #endif
|
|---|
| 712 |
|
|---|
| 713 | The library can be built without support for these APIs, although a
|
|---|
| 714 | standard build will have all implemented APIs. Application programs
|
|---|
| 715 | should check the feature macros before using an API for maximum
|
|---|
| 716 | portability. From libpng 1.5.0 the feature macros set during the build
|
|---|
| 717 | of libpng are recorded in the header file "pnglibconf.h" and this file
|
|---|
| 718 | is always included by png.h.
|
|---|
| 719 |
|
|---|
| 720 | If you don't need to change the library configuration from the default, skip to
|
|---|
| 721 | the next section ("Reading").
|
|---|
| 722 |
|
|---|
| 723 | Notice that some of the makefiles in the 'scripts' directory and (in 1.5.0) all
|
|---|
| 724 | of the build project files in the 'projects' directory simply copy
|
|---|
| 725 | scripts/pnglibconf.h.prebuilt to pnglibconf.h. This means that these build
|
|---|
| 726 | systems do not permit easy auto-configuration of the library - they only
|
|---|
| 727 | support the default configuration.
|
|---|
| 728 |
|
|---|
| 729 | The easiest way to make minor changes to the libpng configuration when
|
|---|
| 730 | auto-configuration is supported is to add definitions to the command line
|
|---|
| 731 | using (typically) CPPFLAGS. For example:
|
|---|
| 732 |
|
|---|
| 733 | CPPFLAGS=\-DPNG_NO_FLOATING_ARITHMETIC
|
|---|
| 734 |
|
|---|
| 735 | will change the internal libpng math implementation for gamma correction and
|
|---|
| 736 | other arithmetic calculations to fixed point, avoiding the need for fast
|
|---|
| 737 | floating point support. The result can be seen in the generated pnglibconf.h -
|
|---|
| 738 | make sure it contains the changed feature macro setting.
|
|---|
| 739 |
|
|---|
| 740 | If you need to make more extensive configuration changes - more than one or two
|
|---|
| 741 | feature macro settings - you can either add \-DPNG_USER_CONFIG to the build
|
|---|
| 742 | command line and put a list of feature macro settings in pngusr.h or you can set
|
|---|
| 743 | DFA_XTRA (a makefile variable) to a file containing the same information in the
|
|---|
| 744 | form of 'option' settings.
|
|---|
| 745 |
|
|---|
| 746 | A. Changing pnglibconf.h
|
|---|
| 747 |
|
|---|
| 748 | A variety of methods exist to build libpng. Not all of these support
|
|---|
| 749 | reconfiguration of pnglibconf.h. To reconfigure pnglibconf.h it must either be
|
|---|
| 750 | rebuilt from scripts/pnglibconf.dfa using awk or it must be edited by hand.
|
|---|
| 751 |
|
|---|
| 752 | Hand editing is achieved by copying scripts/pnglibconf.h.prebuilt to
|
|---|
| 753 | pnglibconf.h and changing the lines defining the supported features, paying
|
|---|
| 754 | very close attention to the 'option' information in scripts/pnglibconf.dfa
|
|---|
| 755 | that describes those features and their requirements. This is easy to get
|
|---|
| 756 | wrong.
|
|---|
| 757 |
|
|---|
| 758 | B. Configuration using DFA_XTRA
|
|---|
| 759 |
|
|---|
| 760 | Rebuilding from pnglibconf.dfa is easy if a functioning 'awk', or a later
|
|---|
| 761 | variant such as 'nawk' or 'gawk', is available. The configure build will
|
|---|
| 762 | automatically find an appropriate awk and build pnglibconf.h.
|
|---|
| 763 | The scripts/pnglibconf.mak file contains a set of make rules for doing the
|
|---|
| 764 | same thing if configure is not used, and many of the makefiles in the scripts
|
|---|
| 765 | directory use this approach.
|
|---|
| 766 |
|
|---|
| 767 | When rebuilding simply write a new file containing changed options and set
|
|---|
| 768 | DFA_XTRA to the name of this file. This causes the build to append the new file
|
|---|
| 769 | to the end of scripts/pnglibconf.dfa. The pngusr.dfa file should contain lines
|
|---|
| 770 | of the following forms:
|
|---|
| 771 |
|
|---|
| 772 | everything = off
|
|---|
| 773 |
|
|---|
| 774 | This turns all optional features off. Include it at the start of pngusr.dfa to
|
|---|
| 775 | make it easier to build a minimal configuration. You will need to turn at least
|
|---|
| 776 | some features on afterward to enable either reading or writing code, or both.
|
|---|
| 777 |
|
|---|
| 778 | option feature on
|
|---|
| 779 | option feature off
|
|---|
| 780 |
|
|---|
| 781 | Enable or disable a single feature. This will automatically enable other
|
|---|
| 782 | features required by a feature that is turned on or disable other features that
|
|---|
| 783 | require a feature which is turned off. Conflicting settings will cause an error
|
|---|
| 784 | message to be emitted by awk.
|
|---|
| 785 |
|
|---|
| 786 | setting feature default value
|
|---|
| 787 |
|
|---|
| 788 | Changes the default value of setting 'feature' to 'value'. There are a small
|
|---|
| 789 | number of settings listed at the top of pnglibconf.h, they are documented in the
|
|---|
| 790 | source code. Most of these values have performance implications for the library
|
|---|
| 791 | but most of them have no visible effect on the API. Some can also be overridden
|
|---|
| 792 | from the API.
|
|---|
| 793 |
|
|---|
| 794 | This method of building a customized pnglibconf.h is illustrated in
|
|---|
| 795 | contrib/pngminim/*. See the "$(PNGCONF):" target in the makefile and
|
|---|
| 796 | pngusr.dfa in these directories.
|
|---|
| 797 |
|
|---|
| 798 | C. Configuration using PNG_USER_CONFIG
|
|---|
| 799 |
|
|---|
| 800 | If \-DPNG_USER_CONFIG is added to the CPPFLAGS when pnglibconf.h is built,
|
|---|
| 801 | the file pngusr.h will automatically be included before the options in
|
|---|
| 802 | scripts/pnglibconf.dfa are processed. Your pngusr.h file should contain only
|
|---|
| 803 | macro definitions turning features on or off or setting settings.
|
|---|
| 804 |
|
|---|
| 805 | Apart from the global setting "everything = off" all the options listed above
|
|---|
| 806 | can be set using macros in pngusr.h:
|
|---|
| 807 |
|
|---|
| 808 | #define PNG_feature_SUPPORTED
|
|---|
| 809 |
|
|---|
| 810 | is equivalent to:
|
|---|
| 811 |
|
|---|
| 812 | option feature on
|
|---|
| 813 |
|
|---|
| 814 | #define PNG_NO_feature
|
|---|
| 815 |
|
|---|
| 816 | is equivalent to:
|
|---|
| 817 |
|
|---|
| 818 | option feature off
|
|---|
| 819 |
|
|---|
| 820 | #define PNG_feature value
|
|---|
| 821 |
|
|---|
| 822 | is equivalent to:
|
|---|
| 823 |
|
|---|
| 824 | setting feature default value
|
|---|
| 825 |
|
|---|
| 826 | Notice that in both cases, pngusr.dfa and pngusr.h, the contents of the
|
|---|
| 827 | pngusr file you supply override the contents of scripts/pnglibconf.dfa
|
|---|
| 828 |
|
|---|
| 829 | If confusing or incomprehensible behavior results it is possible to
|
|---|
| 830 | examine the intermediate file pnglibconf.dfn to find the full set of
|
|---|
| 831 | dependency information for each setting and option. Simply locate the
|
|---|
| 832 | feature in the file and read the C comments that precede it.
|
|---|
| 833 |
|
|---|
| 834 | This method is also illustrated in the contrib/pngminim/* makefiles and
|
|---|
| 835 | pngusr.h.
|
|---|
| 836 |
|
|---|
| 837 | .SH III. Reading
|
|---|
| 838 |
|
|---|
| 839 | We'll now walk you through the possible functions to call when reading
|
|---|
| 840 | in a PNG file sequentially, briefly explaining the syntax and purpose
|
|---|
| 841 | of each one. See example.c and png.h for more detail. While
|
|---|
| 842 | progressive reading is covered in the next section, you will still
|
|---|
| 843 | need some of the functions discussed in this section to read a PNG
|
|---|
| 844 | file.
|
|---|
| 845 |
|
|---|
| 846 | .SS Setup
|
|---|
| 847 |
|
|---|
| 848 | You will want to do the I/O initialization(*) before you get into libpng,
|
|---|
| 849 | so if it doesn't work, you don't have much to undo. Of course, you
|
|---|
| 850 | will also want to insure that you are, in fact, dealing with a PNG
|
|---|
| 851 | file. Libpng provides a simple check to see if a file is a PNG file.
|
|---|
| 852 | To use it, pass in the first 1 to 8 bytes of the file to the function
|
|---|
| 853 | png_sig_cmp(), and it will return 0 (false) if the bytes match the
|
|---|
| 854 | corresponding bytes of the PNG signature, or nonzero (true) otherwise.
|
|---|
| 855 | Of course, the more bytes you pass in, the greater the accuracy of the
|
|---|
| 856 | prediction.
|
|---|
| 857 |
|
|---|
| 858 | If you are intending to keep the file pointer open for use in libpng,
|
|---|
| 859 | you must ensure you don't read more than 8 bytes from the beginning
|
|---|
| 860 | of the file, and you also have to make a call to png_set_sig_bytes()
|
|---|
| 861 | with the number of bytes you read from the beginning. Libpng will
|
|---|
| 862 | then only check the bytes (if any) that your program didn't read.
|
|---|
| 863 |
|
|---|
| 864 | (*): If you are not using the standard I/O functions, you will need
|
|---|
| 865 | to replace them with custom functions. See the discussion under
|
|---|
| 866 | Customizing libpng.
|
|---|
| 867 |
|
|---|
| 868 | FILE *fp = fopen(file_name, "rb");
|
|---|
| 869 | if (!fp)
|
|---|
| 870 | {
|
|---|
| 871 | return ERROR;
|
|---|
| 872 | }
|
|---|
| 873 |
|
|---|
| 874 | if (fread(header, 1, number, fp) != number)
|
|---|
| 875 | {
|
|---|
| 876 | return ERROR;
|
|---|
| 877 | }
|
|---|
| 878 |
|
|---|
| 879 | is_png = !png_sig_cmp(header, 0, number);
|
|---|
| 880 | if (!is_png)
|
|---|
| 881 | {
|
|---|
| 882 | return NOT_PNG;
|
|---|
| 883 | }
|
|---|
| 884 |
|
|---|
| 885 | Next, png_struct and png_info need to be allocated and initialized. In
|
|---|
| 886 | order to ensure that the size of these structures is correct even with a
|
|---|
| 887 | dynamically linked libpng, there are functions to initialize and
|
|---|
| 888 | allocate the structures. We also pass the library version, optional
|
|---|
| 889 | pointers to error handling functions, and a pointer to a data struct for
|
|---|
| 890 | use by the error functions, if necessary (the pointer and functions can
|
|---|
| 891 | be NULL if the default error handlers are to be used). See the section
|
|---|
| 892 | on Changes to Libpng below regarding the old initialization functions.
|
|---|
| 893 | The structure allocation functions quietly return NULL if they fail to
|
|---|
| 894 | create the structure, so your application should check for that.
|
|---|
| 895 |
|
|---|
| 896 | png_structp png_ptr = png_create_read_struct
|
|---|
| 897 | (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
|
|---|
| 898 | user_error_fn, user_warning_fn);
|
|---|
| 899 |
|
|---|
| 900 | if (!png_ptr)
|
|---|
| 901 | return ERROR;
|
|---|
| 902 |
|
|---|
| 903 | png_infop info_ptr = png_create_info_struct(png_ptr);
|
|---|
| 904 |
|
|---|
| 905 | if (!info_ptr)
|
|---|
| 906 | {
|
|---|
| 907 | png_destroy_read_struct(&png_ptr,
|
|---|
| 908 | (png_infopp)NULL, (png_infopp)NULL);
|
|---|
| 909 | return ERROR;
|
|---|
| 910 | }
|
|---|
| 911 |
|
|---|
| 912 | If you want to use your own memory allocation routines,
|
|---|
| 913 | use a libpng that was built with PNG_USER_MEM_SUPPORTED defined, and use
|
|---|
| 914 | png_create_read_struct_2() instead of png_create_read_struct():
|
|---|
| 915 |
|
|---|
| 916 | png_structp png_ptr = png_create_read_struct_2
|
|---|
| 917 | (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
|
|---|
| 918 | user_error_fn, user_warning_fn, (png_voidp)
|
|---|
| 919 | user_mem_ptr, user_malloc_fn, user_free_fn);
|
|---|
| 920 |
|
|---|
| 921 | The error handling routines passed to png_create_read_struct()
|
|---|
| 922 | and the memory alloc/free routines passed to png_create_struct_2()
|
|---|
| 923 | are only necessary if you are not using the libpng supplied error
|
|---|
| 924 | handling and memory alloc/free functions.
|
|---|
| 925 |
|
|---|
| 926 | When libpng encounters an error, it expects to longjmp back
|
|---|
| 927 | to your routine. Therefore, you will need to call setjmp and pass
|
|---|
| 928 | your png_jmpbuf(png_ptr). If you read the file from different
|
|---|
| 929 | routines, you will need to update the longjmp buffer every time you enter
|
|---|
| 930 | a new routine that will call a png_*() function.
|
|---|
| 931 |
|
|---|
| 932 | See your documentation of setjmp/longjmp for your compiler for more
|
|---|
| 933 | information on setjmp/longjmp. See the discussion on libpng error
|
|---|
| 934 | handling in the Customizing Libpng section below for more information
|
|---|
| 935 | on the libpng error handling. If an error occurs, and libpng longjmp's
|
|---|
| 936 | back to your setjmp, you will want to call png_destroy_read_struct() to
|
|---|
| 937 | free any memory.
|
|---|
| 938 |
|
|---|
| 939 | if (setjmp(png_jmpbuf(png_ptr)))
|
|---|
| 940 | {
|
|---|
| 941 | png_destroy_read_struct(&png_ptr, &info_ptr,
|
|---|
| 942 | &end_info);
|
|---|
| 943 | fclose(fp);
|
|---|
| 944 | return ERROR;
|
|---|
| 945 | }
|
|---|
| 946 |
|
|---|
| 947 | Pass (png_infopp)NULL instead of &end_info if you didn't create
|
|---|
| 948 | an end_info structure.
|
|---|
| 949 |
|
|---|
| 950 | If you would rather avoid the complexity of setjmp/longjmp issues,
|
|---|
| 951 | you can compile libpng with PNG_NO_SETJMP, in which case
|
|---|
| 952 | errors will result in a call to PNG_ABORT() which defaults to abort().
|
|---|
| 953 |
|
|---|
| 954 | You can #define PNG_ABORT() to a function that does something
|
|---|
| 955 | more useful than abort(), as long as your function does not
|
|---|
| 956 | return.
|
|---|
| 957 |
|
|---|
| 958 | Now you need to set up the input code. The default for libpng is to
|
|---|
| 959 | use the C function fread(). If you use this, you will need to pass a
|
|---|
| 960 | valid FILE * in the function png_init_io(). Be sure that the file is
|
|---|
| 961 | opened in binary mode. If you wish to handle reading data in another
|
|---|
| 962 | way, you need not call the png_init_io() function, but you must then
|
|---|
| 963 | implement the libpng I/O methods discussed in the Customizing Libpng
|
|---|
| 964 | section below.
|
|---|
| 965 |
|
|---|
| 966 | png_init_io(png_ptr, fp);
|
|---|
| 967 |
|
|---|
| 968 | If you had previously opened the file and read any of the signature from
|
|---|
| 969 | the beginning in order to see if this was a PNG file, you need to let
|
|---|
| 970 | libpng know that there are some bytes missing from the start of the file.
|
|---|
| 971 |
|
|---|
| 972 | png_set_sig_bytes(png_ptr, number);
|
|---|
| 973 |
|
|---|
| 974 | You can change the zlib compression buffer size to be used while
|
|---|
| 975 | reading compressed data with
|
|---|
| 976 |
|
|---|
| 977 | png_set_compression_buffer_size(png_ptr, buffer_size);
|
|---|
| 978 |
|
|---|
| 979 | where the default size is 8192 bytes. Note that the buffer size
|
|---|
| 980 | is changed immediately and the buffer is reallocated immediately,
|
|---|
| 981 | instead of setting a flag to be acted upon later.
|
|---|
| 982 |
|
|---|
| 983 | If you want CRC errors to be handled in a different manner than
|
|---|
| 984 | the default, use
|
|---|
| 985 |
|
|---|
| 986 | png_set_crc_action(png_ptr, crit_action, ancil_action);
|
|---|
| 987 |
|
|---|
| 988 | The values for png_set_crc_action() say how libpng is to handle CRC errors in
|
|---|
| 989 | ancillary and critical chunks, and whether to use the data contained
|
|---|
| 990 | therein. Starting with libpng-1.6.26, this also governs how an ADLER32 error
|
|---|
| 991 | is handled while reading the IDAT chunk. Note that it is impossible to
|
|---|
| 992 | "discard" data in a critical chunk.
|
|---|
| 993 |
|
|---|
| 994 | Choices for (int) crit_action are
|
|---|
| 995 | PNG_CRC_DEFAULT 0 error/quit
|
|---|
| 996 | PNG_CRC_ERROR_QUIT 1 error/quit
|
|---|
| 997 | PNG_CRC_WARN_USE 3 warn/use data
|
|---|
| 998 | PNG_CRC_QUIET_USE 4 quiet/use data
|
|---|
| 999 | PNG_CRC_NO_CHANGE 5 use the current value
|
|---|
| 1000 |
|
|---|
| 1001 | Choices for (int) ancil_action are
|
|---|
| 1002 | PNG_CRC_DEFAULT 0 error/quit
|
|---|
| 1003 | PNG_CRC_ERROR_QUIT 1 error/quit
|
|---|
| 1004 | PNG_CRC_WARN_DISCARD 2 warn/discard data
|
|---|
| 1005 | PNG_CRC_WARN_USE 3 warn/use data
|
|---|
| 1006 | PNG_CRC_QUIET_USE 4 quiet/use data
|
|---|
| 1007 | PNG_CRC_NO_CHANGE 5 use the current value
|
|---|
| 1008 |
|
|---|
| 1009 | When the setting for crit_action is PNG_CRC_QUIET_USE, the CRC and ADLER32
|
|---|
| 1010 | checksums are not only ignored, but they are not evaluated.
|
|---|
| 1011 |
|
|---|
| 1012 | .SS Setting up callback code
|
|---|
| 1013 |
|
|---|
| 1014 | You can set up a callback function to handle any unknown chunks in the
|
|---|
| 1015 | input stream. You must supply the function
|
|---|
| 1016 |
|
|---|
| 1017 | read_chunk_callback(png_structp png_ptr,
|
|---|
| 1018 | png_unknown_chunkp chunk);
|
|---|
| 1019 | {
|
|---|
| 1020 | /* The unknown chunk structure contains your
|
|---|
| 1021 | chunk data, along with similar data for any other
|
|---|
| 1022 | unknown chunks: */
|
|---|
| 1023 |
|
|---|
| 1024 | png_byte name[5];
|
|---|
| 1025 | png_byte *data;
|
|---|
| 1026 | size_t size;
|
|---|
| 1027 |
|
|---|
| 1028 | /* Note that libpng has already taken care of
|
|---|
| 1029 | the CRC handling */
|
|---|
| 1030 |
|
|---|
| 1031 | /* put your code here. Search for your chunk in the
|
|---|
| 1032 | unknown chunk structure, process it, and return one
|
|---|
| 1033 | of the following: */
|
|---|
| 1034 |
|
|---|
| 1035 | return \-n; /* chunk had an error */
|
|---|
| 1036 | return 0; /* did not recognize */
|
|---|
| 1037 | return n; /* success */
|
|---|
| 1038 | }
|
|---|
| 1039 |
|
|---|
| 1040 | (You can give your function another name that you like instead of
|
|---|
| 1041 | "read_chunk_callback")
|
|---|
| 1042 |
|
|---|
| 1043 | To inform libpng about your function, use
|
|---|
| 1044 |
|
|---|
| 1045 | png_set_read_user_chunk_fn(png_ptr, user_chunk_ptr,
|
|---|
| 1046 | read_chunk_callback);
|
|---|
| 1047 |
|
|---|
| 1048 | This names not only the callback function, but also a user pointer that
|
|---|
| 1049 | you can retrieve with
|
|---|
| 1050 |
|
|---|
| 1051 | png_get_user_chunk_ptr(png_ptr);
|
|---|
| 1052 |
|
|---|
| 1053 | If you call the png_set_read_user_chunk_fn() function, then all unknown
|
|---|
| 1054 | chunks which the callback does not handle will be saved when read. You can
|
|---|
| 1055 | cause them to be discarded by returning '1' ("handled") instead of '0'. This
|
|---|
| 1056 | behavior will change in libpng 1.7 and the default handling set by the
|
|---|
| 1057 | png_set_keep_unknown_chunks() function, described below, will be used when the
|
|---|
| 1058 | callback returns 0. If you want the existing behavior you should set the global
|
|---|
| 1059 | default to PNG_HANDLE_CHUNK_IF_SAFE now; this is compatible with all current
|
|---|
| 1060 | versions of libpng and with 1.7. Libpng 1.6 issues a warning if you keep the
|
|---|
| 1061 | default, or PNG_HANDLE_CHUNK_NEVER, and the callback returns 0.
|
|---|
| 1062 |
|
|---|
| 1063 | At this point, you can set up a callback function that will be
|
|---|
| 1064 | called after each row has been read, which you can use to control
|
|---|
| 1065 | a progress meter or the like. It's demonstrated in pngtest.c.
|
|---|
| 1066 | You must supply a function
|
|---|
| 1067 |
|
|---|
| 1068 | void read_row_callback(png_structp png_ptr,
|
|---|
| 1069 | png_uint_32 row, int pass);
|
|---|
| 1070 | {
|
|---|
| 1071 | /* put your code here */
|
|---|
| 1072 | }
|
|---|
| 1073 |
|
|---|
| 1074 | (You can give it another name that you like instead of "read_row_callback")
|
|---|
| 1075 |
|
|---|
| 1076 | To inform libpng about your function, use
|
|---|
| 1077 |
|
|---|
| 1078 | png_set_read_status_fn(png_ptr, read_row_callback);
|
|---|
| 1079 |
|
|---|
| 1080 | When this function is called the row has already been completely processed and
|
|---|
| 1081 | the 'row' and 'pass' refer to the next row to be handled. For the
|
|---|
| 1082 | non-interlaced case the row that was just handled is simply one less than the
|
|---|
| 1083 | passed in row number, and pass will always be 0. For the interlaced case the
|
|---|
| 1084 | same applies unless the row value is 0, in which case the row just handled was
|
|---|
| 1085 | the last one from one of the preceding passes. Because interlacing may skip a
|
|---|
| 1086 | pass you cannot be sure that the preceding pass is just 'pass\-1'; if you really
|
|---|
| 1087 | need to know what the last pass is record (row,pass) from the callback and use
|
|---|
| 1088 | the last recorded value each time.
|
|---|
| 1089 |
|
|---|
| 1090 | As with the user transform you can find the output row using the
|
|---|
| 1091 | PNG_ROW_FROM_PASS_ROW macro.
|
|---|
| 1092 |
|
|---|
| 1093 | .SS Unknown-chunk handling
|
|---|
| 1094 |
|
|---|
| 1095 | Now you get to set the way the library processes unknown chunks in the
|
|---|
| 1096 | input PNG stream. Both known and unknown chunks will be read. Normal
|
|---|
| 1097 | behavior is that known chunks will be parsed into information in
|
|---|
| 1098 | various info_ptr members while unknown chunks will be discarded. This
|
|---|
| 1099 | behavior can be wasteful if your application will never use some known
|
|---|
| 1100 | chunk types. To change this, you can call:
|
|---|
| 1101 |
|
|---|
| 1102 | png_set_keep_unknown_chunks(png_ptr, keep,
|
|---|
| 1103 | chunk_list, num_chunks);
|
|---|
| 1104 |
|
|---|
| 1105 | keep - 0: default unknown chunk handling
|
|---|
| 1106 | 1: ignore; do not keep
|
|---|
| 1107 | 2: keep only if safe-to-copy
|
|---|
| 1108 | 3: keep even if unsafe-to-copy
|
|---|
| 1109 |
|
|---|
| 1110 | You can use these definitions:
|
|---|
| 1111 | PNG_HANDLE_CHUNK_AS_DEFAULT 0
|
|---|
| 1112 | PNG_HANDLE_CHUNK_NEVER 1
|
|---|
| 1113 | PNG_HANDLE_CHUNK_IF_SAFE 2
|
|---|
| 1114 | PNG_HANDLE_CHUNK_ALWAYS 3
|
|---|
| 1115 |
|
|---|
| 1116 | chunk_list - list of chunks affected (a byte string,
|
|---|
| 1117 | five bytes per chunk, NULL or '\0' if
|
|---|
| 1118 | num_chunks is positive; ignored if
|
|---|
| 1119 | numchunks <= 0).
|
|---|
| 1120 |
|
|---|
| 1121 | num_chunks - number of chunks affected; if 0, all
|
|---|
| 1122 | unknown chunks are affected. If positive,
|
|---|
| 1123 | only the chunks in the list are affected,
|
|---|
| 1124 | and if negative all unknown chunks and
|
|---|
| 1125 | all known chunks except for the IHDR,
|
|---|
| 1126 | PLTE, tRNS, IDAT, and IEND chunks are
|
|---|
| 1127 | affected.
|
|---|
| 1128 |
|
|---|
| 1129 | Unknown chunks declared in this way will be saved as raw data onto a
|
|---|
| 1130 | list of png_unknown_chunk structures. If a chunk that is normally
|
|---|
| 1131 | known to libpng is named in the list, it will be handled as unknown,
|
|---|
| 1132 | according to the "keep" directive. If a chunk is named in successive
|
|---|
| 1133 | instances of png_set_keep_unknown_chunks(), the final instance will
|
|---|
| 1134 | take precedence. The IHDR and IEND chunks should not be named in
|
|---|
| 1135 | chunk_list; if they are, libpng will process them normally anyway.
|
|---|
| 1136 | If you know that your application will never make use of some particular
|
|---|
| 1137 | chunks, use PNG_HANDLE_CHUNK_NEVER (or 1) as demonstrated below.
|
|---|
| 1138 |
|
|---|
| 1139 | Here is an example of the usage of png_set_keep_unknown_chunks(),
|
|---|
| 1140 | where the private "vpAg" chunk will later be processed by a user chunk
|
|---|
| 1141 | callback function:
|
|---|
| 1142 |
|
|---|
| 1143 | png_byte vpAg[5]={118, 112, 65, 103, (png_byte) '\0'};
|
|---|
| 1144 |
|
|---|
| 1145 | #if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
|
|---|
| 1146 | png_byte unused_chunks[]=
|
|---|
| 1147 | {
|
|---|
| 1148 | 104, 73, 83, 84, (png_byte) '\0', /* hIST */
|
|---|
| 1149 | 105, 84, 88, 116, (png_byte) '\0', /* iTXt */
|
|---|
| 1150 | 112, 67, 65, 76, (png_byte) '\0', /* pCAL */
|
|---|
| 1151 | 115, 67, 65, 76, (png_byte) '\0', /* sCAL */
|
|---|
| 1152 | 115, 80, 76, 84, (png_byte) '\0', /* sPLT */
|
|---|
| 1153 | 116, 73, 77, 69, (png_byte) '\0', /* tIME */
|
|---|
| 1154 | };
|
|---|
| 1155 | #endif
|
|---|
| 1156 |
|
|---|
| 1157 | ...
|
|---|
| 1158 |
|
|---|
| 1159 | #if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
|
|---|
| 1160 | /* ignore all unknown chunks
|
|---|
| 1161 | * (use global setting "2" for libpng16 and earlier):
|
|---|
| 1162 | */
|
|---|
| 1163 | png_set_keep_unknown_chunks(read_ptr, 2, NULL, 0);
|
|---|
| 1164 |
|
|---|
| 1165 | /* except for vpAg: */
|
|---|
| 1166 | png_set_keep_unknown_chunks(read_ptr, 2, vpAg, 1);
|
|---|
| 1167 |
|
|---|
| 1168 | /* also ignore unused known chunks: */
|
|---|
| 1169 | png_set_keep_unknown_chunks(read_ptr, 1, unused_chunks,
|
|---|
| 1170 | (int)(sizeof unused_chunks)/5);
|
|---|
| 1171 | #endif
|
|---|
| 1172 |
|
|---|
| 1173 | .SS User limits
|
|---|
| 1174 |
|
|---|
| 1175 | The PNG specification allows the width and height of an image to be as
|
|---|
| 1176 | large as 2^(31\-1 (0x7fffffff), or about 2.147 billion rows and columns.
|
|---|
| 1177 | For safety, libpng imposes a default limit of 1 million rows and columns.
|
|---|
| 1178 | Larger images will be rejected immediately with a png_error() call. If
|
|---|
| 1179 | you wish to change these limits, you can use
|
|---|
| 1180 |
|
|---|
| 1181 | png_set_user_limits(png_ptr, width_max, height_max);
|
|---|
| 1182 |
|
|---|
| 1183 | to set your own limits (libpng may reject some very wide images
|
|---|
| 1184 | anyway because of potential buffer overflow conditions).
|
|---|
| 1185 |
|
|---|
| 1186 | You should put this statement after you create the PNG structure and
|
|---|
| 1187 | before calling png_read_info(), png_read_png(), or png_process_data().
|
|---|
| 1188 |
|
|---|
| 1189 | When writing a PNG datastream, put this statement before calling
|
|---|
| 1190 | png_write_info() or png_write_png().
|
|---|
| 1191 |
|
|---|
| 1192 | If you need to retrieve the limits that are being applied, use
|
|---|
| 1193 |
|
|---|
| 1194 | width_max = png_get_user_width_max(png_ptr);
|
|---|
| 1195 | height_max = png_get_user_height_max(png_ptr);
|
|---|
| 1196 |
|
|---|
| 1197 | The PNG specification sets no limit on the number of ancillary chunks
|
|---|
| 1198 | allowed in a PNG datastream. By default, libpng imposes a limit of
|
|---|
| 1199 | a total of 1000 sPLT, tEXt, iTXt, zTXt, and unknown chunks to be stored.
|
|---|
| 1200 | If you have set up both info_ptr and end_info_ptr, the limit applies
|
|---|
| 1201 | separately to each. You can change the limit on the total number of such
|
|---|
| 1202 | chunks that will be stored, with
|
|---|
| 1203 |
|
|---|
| 1204 | png_set_chunk_cache_max(png_ptr, user_chunk_cache_max);
|
|---|
| 1205 |
|
|---|
| 1206 | where 0x7fffffffL means unlimited. You can retrieve this limit with
|
|---|
| 1207 |
|
|---|
| 1208 | chunk_cache_max = png_get_chunk_cache_max(png_ptr);
|
|---|
| 1209 |
|
|---|
| 1210 | Libpng imposes a limit of 8 Megabytes (8,000,000 bytes) on the amount of
|
|---|
| 1211 | memory that any chunk other than IDAT can occupy, originally or when
|
|---|
| 1212 | decompressed (prior to libpng-1.6.32 the limit was only applied to compressed
|
|---|
| 1213 | chunks after decompression). You can change this limit with
|
|---|
| 1214 |
|
|---|
| 1215 | png_set_chunk_malloc_max(png_ptr, user_chunk_malloc_max);
|
|---|
| 1216 |
|
|---|
| 1217 | and you can retrieve the limit with
|
|---|
| 1218 |
|
|---|
| 1219 | chunk_malloc_max = png_get_chunk_malloc_max(png_ptr);
|
|---|
| 1220 |
|
|---|
| 1221 | Any chunks that would cause either of these limits to be exceeded will
|
|---|
| 1222 | be ignored.
|
|---|
| 1223 |
|
|---|
| 1224 | .SS Information about your system
|
|---|
| 1225 |
|
|---|
| 1226 | If you intend to display the PNG or to incorporate it in other image data you
|
|---|
| 1227 | need to tell libpng information about your display or drawing surface so that
|
|---|
| 1228 | libpng can convert the values in the image to match the display.
|
|---|
| 1229 |
|
|---|
| 1230 | From libpng-1.5.4 this information can be set before reading the PNG file
|
|---|
| 1231 | header. In earlier versions png_set_gamma() existed but behaved incorrectly if
|
|---|
| 1232 | called before the PNG file header had been read and png_set_alpha_mode() did not
|
|---|
| 1233 | exist.
|
|---|
| 1234 |
|
|---|
| 1235 | If you need to support versions prior to libpng-1.5.4 test the version number
|
|---|
| 1236 | as illustrated below using "PNG_LIBPNG_VER >= 10504" and follow the procedures
|
|---|
| 1237 | described in the appropriate manual page.
|
|---|
| 1238 |
|
|---|
| 1239 | You give libpng the encoding expected by your system expressed as a 'gamma'
|
|---|
| 1240 | value. You can also specify a default encoding for the PNG file in
|
|---|
| 1241 | case the required information is missing from the file. By default libpng
|
|---|
| 1242 | assumes that the PNG data matches your system, to keep this default call:
|
|---|
| 1243 |
|
|---|
| 1244 | png_set_gamma(png_ptr, screen_gamma, output_gamma);
|
|---|
| 1245 |
|
|---|
| 1246 | or you can use the fixed point equivalent:
|
|---|
| 1247 |
|
|---|
| 1248 | png_set_gamma_fixed(png_ptr, PNG_FP_1*screen_gamma,
|
|---|
| 1249 | PNG_FP_1*output_gamma);
|
|---|
| 1250 |
|
|---|
| 1251 | If you don't know the gamma for your system it is probably 2.2 - a good
|
|---|
| 1252 | approximation to the IEC standard for display systems (sRGB). If images are
|
|---|
| 1253 | too contrasty or washed out you got the value wrong - check your system
|
|---|
| 1254 | documentation!
|
|---|
| 1255 |
|
|---|
| 1256 | Many systems permit the system gamma to be changed via a lookup table in the
|
|---|
| 1257 | display driver, a few systems, including older Macs, change the response by
|
|---|
| 1258 | default. As of 1.5.4 three special values are available to handle common
|
|---|
| 1259 | situations:
|
|---|
| 1260 |
|
|---|
| 1261 | PNG_DEFAULT_sRGB: Indicates that the system conforms to the
|
|---|
| 1262 | IEC 61966-2-1 standard. This matches almost
|
|---|
| 1263 | all systems.
|
|---|
| 1264 | PNG_GAMMA_MAC_18: Indicates that the system is an older
|
|---|
| 1265 | (pre Mac OS 10.6) Apple Macintosh system with
|
|---|
| 1266 | the default settings.
|
|---|
| 1267 | PNG_GAMMA_LINEAR: Just the fixed point value for 1.0 - indicates
|
|---|
| 1268 | that the system expects data with no gamma
|
|---|
| 1269 | encoding.
|
|---|
| 1270 |
|
|---|
| 1271 | You would use the linear (unencoded) value if you need to process the pixel
|
|---|
| 1272 | values further because this avoids the need to decode and re-encode each
|
|---|
| 1273 | component value whenever arithmetic is performed. A lot of graphics software
|
|---|
| 1274 | uses linear values for this reason, often with higher precision component values
|
|---|
| 1275 | to preserve overall accuracy.
|
|---|
| 1276 |
|
|---|
| 1277 |
|
|---|
| 1278 | The output_gamma value expresses how to decode the output values, not how
|
|---|
| 1279 | they are encoded. The values used correspond to the normal numbers used to
|
|---|
| 1280 | describe the overall gamma of a computer display system; for example 2.2 for
|
|---|
| 1281 | an sRGB conformant system. The values are scaled by 100000 in the _fixed
|
|---|
| 1282 | version of the API (so 220000 for sRGB.)
|
|---|
| 1283 |
|
|---|
| 1284 | The inverse of the value is always used to provide a default for the PNG file
|
|---|
| 1285 | encoding if it has no gAMA chunk and if png_set_gamma() has not been called
|
|---|
| 1286 | to override the PNG gamma information.
|
|---|
| 1287 |
|
|---|
| 1288 | When the ALPHA_OPTIMIZED mode is selected the output gamma is used to encode
|
|---|
| 1289 | opaque pixels however pixels with lower alpha values are not encoded,
|
|---|
| 1290 | regardless of the output gamma setting.
|
|---|
| 1291 |
|
|---|
| 1292 | When the standard Porter Duff handling is requested with mode 1 the output
|
|---|
| 1293 | encoding is set to be linear and the output_gamma value is only relevant
|
|---|
| 1294 | as a default for input data that has no gamma information. The linear output
|
|---|
| 1295 | encoding will be overridden if png_set_gamma() is called - the results may be
|
|---|
| 1296 | highly unexpected!
|
|---|
| 1297 |
|
|---|
| 1298 | The following numbers are derived from the sRGB standard and the research
|
|---|
| 1299 | behind it. sRGB is defined to be approximated by a PNG gAMA chunk value of
|
|---|
| 1300 | 0.45455 (1/2.2) for PNG. The value implicitly includes any viewing
|
|---|
| 1301 | correction required to take account of any differences in the color
|
|---|
| 1302 | environment of the original scene and the intended display environment; the
|
|---|
| 1303 | value expresses how to *decode* the image for display, not how the original
|
|---|
| 1304 | data was *encoded*.
|
|---|
| 1305 |
|
|---|
| 1306 | sRGB provides a peg for the PNG standard by defining a viewing environment.
|
|---|
| 1307 | sRGB itself, and earlier TV standards, actually use a more complex transform
|
|---|
| 1308 | (a linear portion then a gamma 2.4 power law) than PNG can express. (PNG is
|
|---|
| 1309 | limited to simple power laws.) By saying that an image for direct display on
|
|---|
| 1310 | an sRGB conformant system should be stored with a gAMA chunk value of 45455
|
|---|
| 1311 | (11.3.3.2 and 11.3.3.5 of the ISO PNG specification) the PNG specification
|
|---|
| 1312 | makes it possible to derive values for other display systems and
|
|---|
| 1313 | environments.
|
|---|
| 1314 |
|
|---|
| 1315 | The Mac value is deduced from the sRGB based on an assumption that the actual
|
|---|
| 1316 | extra viewing correction used in early Mac display systems was implemented as
|
|---|
| 1317 | a power 1.45 lookup table.
|
|---|
| 1318 |
|
|---|
| 1319 | Any system where a programmable lookup table is used or where the behavior of
|
|---|
| 1320 | the final display device characteristics can be changed requires system
|
|---|
| 1321 | specific code to obtain the current characteristic. However this can be
|
|---|
| 1322 | difficult and most PNG gamma correction only requires an approximate value.
|
|---|
| 1323 |
|
|---|
| 1324 | By default, if png_set_alpha_mode() is not called, libpng assumes that all
|
|---|
| 1325 | values are unencoded, linear, values and that the output device also has a
|
|---|
| 1326 | linear characteristic. This is only very rarely correct - it is invariably
|
|---|
| 1327 | better to call png_set_alpha_mode() with PNG_DEFAULT_sRGB than rely on the
|
|---|
| 1328 | default if you don't know what the right answer is!
|
|---|
| 1329 |
|
|---|
| 1330 | The special value PNG_GAMMA_MAC_18 indicates an older Mac system (pre Mac OS
|
|---|
| 1331 | 10.6) which used a correction table to implement a somewhat lower gamma on an
|
|---|
| 1332 | otherwise sRGB system.
|
|---|
| 1333 |
|
|---|
| 1334 | Both these values are reserved (not simple gamma values) in order to allow
|
|---|
| 1335 | more precise correction internally in the future.
|
|---|
| 1336 |
|
|---|
| 1337 | NOTE: the values can be passed to either the fixed or floating
|
|---|
| 1338 | point APIs, but the floating point API will also accept floating point
|
|---|
| 1339 | values.
|
|---|
| 1340 |
|
|---|
| 1341 | The second thing you may need to tell libpng about is how your system handles
|
|---|
| 1342 | alpha channel information. Some, but not all, PNG files contain an alpha
|
|---|
| 1343 | channel. To display these files correctly you need to compose the data onto a
|
|---|
| 1344 | suitable background, as described in the PNG specification.
|
|---|
| 1345 |
|
|---|
| 1346 | Libpng only supports composing onto a single color (using png_set_background;
|
|---|
| 1347 | see below). Otherwise you must do the composition yourself and, in this case,
|
|---|
| 1348 | you may need to call png_set_alpha_mode:
|
|---|
| 1349 |
|
|---|
| 1350 | #if PNG_LIBPNG_VER >= 10504
|
|---|
| 1351 | png_set_alpha_mode(png_ptr, mode, screen_gamma);
|
|---|
| 1352 | #else
|
|---|
| 1353 | png_set_gamma(png_ptr, screen_gamma, 1.0/screen_gamma);
|
|---|
| 1354 | #endif
|
|---|
| 1355 |
|
|---|
| 1356 | The screen_gamma value is the same as the argument to png_set_gamma; however,
|
|---|
| 1357 | how it affects the output depends on the mode. png_set_alpha_mode() sets the
|
|---|
| 1358 | file gamma default to 1/screen_gamma, so normally you don't need to call
|
|---|
| 1359 | png_set_gamma. If you need different defaults call png_set_gamma() before
|
|---|
| 1360 | png_set_alpha_mode() - if you call it after it will override the settings made
|
|---|
| 1361 | by png_set_alpha_mode().
|
|---|
| 1362 |
|
|---|
| 1363 | The mode is as follows:
|
|---|
| 1364 |
|
|---|
| 1365 | PNG_ALPHA_PNG: The data is encoded according to the PNG
|
|---|
| 1366 | specification. Red, green and blue, or gray, components are
|
|---|
| 1367 | gamma encoded color values and are not premultiplied by the
|
|---|
| 1368 | alpha value. The alpha value is a linear measure of the
|
|---|
| 1369 | contribution of the pixel to the corresponding final output pixel.
|
|---|
| 1370 |
|
|---|
| 1371 | You should normally use this format if you intend to perform
|
|---|
| 1372 | color correction on the color values; most, maybe all, color
|
|---|
| 1373 | correction software has no handling for the alpha channel and,
|
|---|
| 1374 | anyway, the math to handle pre-multiplied component values is
|
|---|
| 1375 | unnecessarily complex.
|
|---|
| 1376 |
|
|---|
| 1377 | Before you do any arithmetic on the component values you need
|
|---|
| 1378 | to remove the gamma encoding and multiply out the alpha
|
|---|
| 1379 | channel. See the PNG specification for more detail. It is
|
|---|
| 1380 | important to note that when an image with an alpha channel is
|
|---|
| 1381 | scaled, linear encoded, pre-multiplied component values must
|
|---|
| 1382 | be used!
|
|---|
| 1383 |
|
|---|
| 1384 | The remaining modes assume you don't need to do any further color correction or
|
|---|
| 1385 | that if you do, your color correction software knows all about alpha (it
|
|---|
| 1386 | probably doesn't!). They 'associate' the alpha with the color information by
|
|---|
| 1387 | storing color channel values that have been scaled by the alpha. The
|
|---|
| 1388 | advantage is that the color channels can be resampled (the image can be
|
|---|
| 1389 | scaled) in this form. The disadvantage is that normal practice is to store
|
|---|
| 1390 | linear, not (gamma) encoded, values and this requires 16-bit channels for
|
|---|
| 1391 | still images rather than the 8-bit channels that are just about sufficient if
|
|---|
| 1392 | gamma encoding is used. In addition all non-transparent pixel values,
|
|---|
| 1393 | including completely opaque ones, must be gamma encoded to produce the final
|
|---|
| 1394 | image. These are the 'STANDARD', 'ASSOCIATED' or 'PREMULTIPLIED' modes
|
|---|
| 1395 | described below (the latter being the two common names for associated alpha
|
|---|
| 1396 | color channels). Note that PNG files always contain non-associated color
|
|---|
| 1397 | channels; png_set_alpha_mode() with one of the modes causes the decoder to
|
|---|
| 1398 | convert the pixels to an associated form before returning them to your
|
|---|
| 1399 | application.
|
|---|
| 1400 |
|
|---|
| 1401 | Since it is not necessary to perform arithmetic on opaque color values so
|
|---|
| 1402 | long as they are not to be resampled and are in the final color space it is
|
|---|
| 1403 | possible to optimize the handling of alpha by storing the opaque pixels in
|
|---|
| 1404 | the PNG format (adjusted for the output color space) while storing partially
|
|---|
| 1405 | opaque pixels in the standard, linear, format. The accuracy required for
|
|---|
| 1406 | standard alpha composition is relatively low, because the pixels are
|
|---|
| 1407 | isolated, therefore typically the accuracy loss in storing 8-bit linear
|
|---|
| 1408 | values is acceptable. (This is not true if the alpha channel is used to
|
|---|
| 1409 | simulate transparency over large areas - use 16 bits or the PNG mode in
|
|---|
| 1410 | this case!) This is the 'OPTIMIZED' mode. For this mode a pixel is
|
|---|
| 1411 | treated as opaque only if the alpha value is equal to the maximum value.
|
|---|
| 1412 |
|
|---|
| 1413 | PNG_ALPHA_STANDARD: The data libpng produces is encoded in the
|
|---|
| 1414 | standard way assumed by most correctly written graphics software.
|
|---|
| 1415 | The gamma encoding will be removed by libpng and the
|
|---|
| 1416 | linear component values will be pre-multiplied by the
|
|---|
| 1417 | alpha channel.
|
|---|
| 1418 |
|
|---|
| 1419 | With this format the final image must be re-encoded to
|
|---|
| 1420 | match the display gamma before the image is displayed.
|
|---|
| 1421 | If your system doesn't do that, yet still seems to
|
|---|
| 1422 | perform arithmetic on the pixels without decoding them,
|
|---|
| 1423 | it is broken - check out the modes below.
|
|---|
| 1424 |
|
|---|
| 1425 | With PNG_ALPHA_STANDARD libpng always produces linear
|
|---|
| 1426 | component values, whatever screen_gamma you supply. The
|
|---|
| 1427 | screen_gamma value is, however, used as a default for
|
|---|
| 1428 | the file gamma if the PNG file has no gamma information.
|
|---|
| 1429 |
|
|---|
| 1430 | If you call png_set_gamma() after png_set_alpha_mode() you
|
|---|
| 1431 | will override the linear encoding. Instead the
|
|---|
| 1432 | pre-multiplied pixel values will be gamma encoded but
|
|---|
| 1433 | the alpha channel will still be linear. This may
|
|---|
| 1434 | actually match the requirements of some broken software,
|
|---|
| 1435 | but it is unlikely.
|
|---|
| 1436 |
|
|---|
| 1437 | While linear 8-bit data is often used it has
|
|---|
| 1438 | insufficient precision for any image with a reasonable
|
|---|
| 1439 | dynamic range. To avoid problems, and if your software
|
|---|
| 1440 | supports it, use png_set_expand_16() to force all
|
|---|
| 1441 | components to 16 bits.
|
|---|
| 1442 |
|
|---|
| 1443 | PNG_ALPHA_OPTIMIZED: This mode is the same as PNG_ALPHA_STANDARD
|
|---|
| 1444 | except that completely opaque pixels are gamma encoded according to
|
|---|
| 1445 | the screen_gamma value. Pixels with alpha less than 1.0
|
|---|
| 1446 | will still have linear components.
|
|---|
| 1447 |
|
|---|
| 1448 | Use this format if you have control over your
|
|---|
| 1449 | compositing software and so don't do other arithmetic
|
|---|
| 1450 | (such as scaling) on the data you get from libpng. Your
|
|---|
| 1451 | compositing software can simply copy opaque pixels to
|
|---|
| 1452 | the output but still has linear values for the
|
|---|
| 1453 | non-opaque pixels.
|
|---|
| 1454 |
|
|---|
| 1455 | In normal compositing, where the alpha channel encodes
|
|---|
| 1456 | partial pixel coverage (as opposed to broad area
|
|---|
| 1457 | translucency), the inaccuracies of the 8-bit
|
|---|
| 1458 | representation of non-opaque pixels are irrelevant.
|
|---|
| 1459 |
|
|---|
| 1460 | You can also try this format if your software is broken;
|
|---|
| 1461 | it might look better.
|
|---|
| 1462 |
|
|---|
| 1463 | PNG_ALPHA_BROKEN: This is PNG_ALPHA_STANDARD; however, all component
|
|---|
| 1464 | values, including the alpha channel are gamma encoded. This is
|
|---|
| 1465 | broken because, in practice, no implementation that uses this choice
|
|---|
| 1466 | correctly undoes the encoding before handling alpha composition. Use this
|
|---|
| 1467 | choice only if other serious errors in the software or hardware you use
|
|---|
| 1468 | mandate it. In most cases of broken software or hardware the bug in the
|
|---|
| 1469 | final display manifests as a subtle halo around composited parts of the
|
|---|
| 1470 | image. You may not even perceive this as a halo; the composited part of
|
|---|
| 1471 | the image may simply appear separate from the background, as though it had
|
|---|
| 1472 | been cut out of paper and pasted on afterward.
|
|---|
| 1473 |
|
|---|
| 1474 | If you don't have to deal with bugs in software or hardware, or if you can fix
|
|---|
| 1475 | them, there are three recommended ways of using png_set_alpha_mode():
|
|---|
| 1476 |
|
|---|
| 1477 | png_set_alpha_mode(png_ptr, PNG_ALPHA_PNG,
|
|---|
| 1478 | screen_gamma);
|
|---|
| 1479 |
|
|---|
| 1480 | You can do color correction on the result (libpng does not currently
|
|---|
| 1481 | support color correction internally). When you handle the alpha channel
|
|---|
| 1482 | you need to undo the gamma encoding and multiply out the alpha.
|
|---|
| 1483 |
|
|---|
| 1484 | png_set_alpha_mode(png_ptr, PNG_ALPHA_STANDARD,
|
|---|
| 1485 | screen_gamma);
|
|---|
| 1486 | png_set_expand_16(png_ptr);
|
|---|
| 1487 |
|
|---|
| 1488 | If you are using the high level interface, don't call png_set_expand_16();
|
|---|
| 1489 | instead pass PNG_TRANSFORM_EXPAND_16 to the interface.
|
|---|
| 1490 |
|
|---|
| 1491 | With this mode you can't do color correction, but you can do arithmetic,
|
|---|
| 1492 | including composition and scaling, on the data without further processing.
|
|---|
| 1493 |
|
|---|
| 1494 | png_set_alpha_mode(png_ptr, PNG_ALPHA_OPTIMIZED,
|
|---|
| 1495 | screen_gamma);
|
|---|
| 1496 |
|
|---|
| 1497 | You can avoid the expansion to 16-bit components with this mode, but you
|
|---|
| 1498 | lose the ability to scale the image or perform other linear arithmetic.
|
|---|
| 1499 | All you can do is compose the result onto a matching output. Since this
|
|---|
| 1500 | mode is libpng-specific you also need to write your own composition
|
|---|
| 1501 | software.
|
|---|
| 1502 |
|
|---|
| 1503 | The following are examples of calls to png_set_alpha_mode to achieve the
|
|---|
| 1504 | required overall gamma correction and, where necessary, alpha
|
|---|
| 1505 | premultiplication.
|
|---|
| 1506 |
|
|---|
| 1507 | png_set_alpha_mode(pp, PNG_ALPHA_PNG, PNG_DEFAULT_sRGB);
|
|---|
| 1508 |
|
|---|
| 1509 | Choices for the alpha_mode are
|
|---|
| 1510 |
|
|---|
| 1511 | PNG_ALPHA_PNG 0 /* according to the PNG standard */
|
|---|
| 1512 | PNG_ALPHA_STANDARD 1 /* according to Porter/Duff */
|
|---|
| 1513 | PNG_ALPHA_ASSOCIATED 1 /* as above; this is the normal practice */
|
|---|
| 1514 | PNG_ALPHA_PREMULTIPLIED 1 /* as above */
|
|---|
| 1515 | PNG_ALPHA_OPTIMIZED 2 /* 'PNG' for opaque pixels, else 'STANDARD' */
|
|---|
| 1516 | PNG_ALPHA_BROKEN 3 /* the alpha channel is gamma encoded */
|
|---|
| 1517 |
|
|---|
| 1518 | PNG_ALPHA_PNG is the default libpng handling of the alpha channel. It is not
|
|---|
| 1519 | pre-multiplied into the color components. In addition the call states
|
|---|
| 1520 | that the output is for a sRGB system and causes all PNG files without gAMA
|
|---|
| 1521 | chunks to be assumed to be encoded using sRGB.
|
|---|
| 1522 |
|
|---|
| 1523 | png_set_alpha_mode(pp, PNG_ALPHA_PNG, PNG_GAMMA_MAC);
|
|---|
| 1524 |
|
|---|
| 1525 | In this case the output is assumed to be something like an sRGB conformant
|
|---|
| 1526 | display preceded by a power-law lookup table of power 1.45. This is how
|
|---|
| 1527 | early Mac systems behaved.
|
|---|
| 1528 |
|
|---|
| 1529 | png_set_alpha_mode(pp, PNG_ALPHA_STANDARD, PNG_GAMMA_LINEAR);
|
|---|
| 1530 |
|
|---|
| 1531 | This is the classic Jim Blinn approach and will work in academic
|
|---|
| 1532 | environments where everything is done by the book. It has the shortcoming
|
|---|
| 1533 | of assuming that input PNG data with no gamma information is linear - this
|
|---|
| 1534 | is unlikely to be correct unless the PNG files were generated locally.
|
|---|
| 1535 | Most of the time the output precision will be so low as to show
|
|---|
| 1536 | significant banding in dark areas of the image.
|
|---|
| 1537 |
|
|---|
| 1538 | png_set_expand_16(pp);
|
|---|
| 1539 | png_set_alpha_mode(pp, PNG_ALPHA_STANDARD, PNG_DEFAULT_sRGB);
|
|---|
| 1540 |
|
|---|
| 1541 | This is a somewhat more realistic Jim Blinn inspired approach. PNG files
|
|---|
| 1542 | are assumed to have the sRGB encoding if not marked with a gamma value and
|
|---|
| 1543 | the output is always 16 bits per component. This permits accurate scaling
|
|---|
| 1544 | and processing of the data. If you know that your input PNG files were
|
|---|
| 1545 | generated locally you might need to replace PNG_DEFAULT_sRGB with the
|
|---|
| 1546 | correct value for your system.
|
|---|
| 1547 |
|
|---|
| 1548 | png_set_alpha_mode(pp, PNG_ALPHA_OPTIMIZED, PNG_DEFAULT_sRGB);
|
|---|
| 1549 |
|
|---|
| 1550 | If you just need to composite the PNG image onto an existing background
|
|---|
| 1551 | and if you control the code that does this you can use the optimization
|
|---|
| 1552 | setting. In this case you just copy completely opaque pixels to the
|
|---|
| 1553 | output. For pixels that are not completely transparent (you just skip
|
|---|
| 1554 | those) you do the composition math using png_composite or png_composite_16
|
|---|
| 1555 | below then encode the resultant 8-bit or 16-bit values to match the output
|
|---|
| 1556 | encoding.
|
|---|
| 1557 |
|
|---|
| 1558 | Other cases
|
|---|
| 1559 |
|
|---|
| 1560 | If neither the PNG nor the standard linear encoding work for you because
|
|---|
| 1561 | of the software or hardware you use then you have a big problem. The PNG
|
|---|
| 1562 | case will probably result in halos around the image. The linear encoding
|
|---|
| 1563 | will probably result in a washed out, too bright, image (it's actually too
|
|---|
| 1564 | contrasty.) Try the ALPHA_OPTIMIZED mode above - this will probably
|
|---|
| 1565 | substantially reduce the halos. Alternatively try:
|
|---|
| 1566 |
|
|---|
| 1567 | png_set_alpha_mode(pp, PNG_ALPHA_BROKEN, PNG_DEFAULT_sRGB);
|
|---|
| 1568 |
|
|---|
| 1569 | This option will also reduce the halos, but there will be slight dark
|
|---|
| 1570 | halos round the opaque parts of the image where the background is light.
|
|---|
| 1571 | In the OPTIMIZED mode the halos will be light halos where the background
|
|---|
| 1572 | is dark. Take your pick - the halos are unavoidable unless you can get
|
|---|
| 1573 | your hardware/software fixed! (The OPTIMIZED approach is slightly
|
|---|
| 1574 | faster.)
|
|---|
| 1575 |
|
|---|
| 1576 | When the default gamma of PNG files doesn't match the output gamma.
|
|---|
| 1577 | If you have PNG files with no gamma information png_set_alpha_mode allows
|
|---|
| 1578 | you to provide a default gamma, but it also sets the output gamma to the
|
|---|
| 1579 | matching value. If you know your PNG files have a gamma that doesn't
|
|---|
| 1580 | match the output you can take advantage of the fact that
|
|---|
| 1581 | png_set_alpha_mode always sets the output gamma but only sets the PNG
|
|---|
| 1582 | default if it is not already set:
|
|---|
| 1583 |
|
|---|
| 1584 | png_set_alpha_mode(pp, PNG_ALPHA_PNG, PNG_DEFAULT_sRGB);
|
|---|
| 1585 | png_set_alpha_mode(pp, PNG_ALPHA_PNG, PNG_GAMMA_MAC);
|
|---|
| 1586 |
|
|---|
| 1587 | The first call sets both the default and the output gamma values, the
|
|---|
| 1588 | second call overrides the output gamma without changing the default. This
|
|---|
| 1589 | is easier than achieving the same effect with png_set_gamma. You must use
|
|---|
| 1590 | PNG_ALPHA_PNG for the first call - internal checking in png_set_alpha will
|
|---|
| 1591 | fire if more than one call to png_set_alpha_mode and png_set_background is
|
|---|
| 1592 | made in the same read operation, however multiple calls with PNG_ALPHA_PNG
|
|---|
| 1593 | are ignored.
|
|---|
| 1594 |
|
|---|
| 1595 | If you don't need, or can't handle, the alpha channel you can call
|
|---|
| 1596 | png_set_background() to remove it by compositing against a fixed color. Don't
|
|---|
| 1597 | call png_set_strip_alpha() to do this - it will leave spurious pixel values in
|
|---|
| 1598 | transparent parts of this image.
|
|---|
| 1599 |
|
|---|
| 1600 | png_set_background(png_ptr, &background_color,
|
|---|
| 1601 | PNG_BACKGROUND_GAMMA_SCREEN, 0, 1);
|
|---|
| 1602 |
|
|---|
| 1603 | The background_color is an RGB or grayscale value according to the data format
|
|---|
| 1604 | libpng will produce for you. Because you don't yet know the format of the PNG
|
|---|
| 1605 | file, if you call png_set_background at this point you must arrange for the
|
|---|
| 1606 | format produced by libpng to always have 8-bit or 16-bit components and then
|
|---|
| 1607 | store the color as an 8-bit or 16-bit color as appropriate. The color contains
|
|---|
| 1608 | separate gray and RGB component values, so you can let libpng produce gray or
|
|---|
| 1609 | RGB output according to the input format, but low bit depth grayscale images
|
|---|
| 1610 | must always be converted to at least 8-bit format. (Even though low bit depth
|
|---|
| 1611 | grayscale images can't have an alpha channel they can have a transparent
|
|---|
| 1612 | color!)
|
|---|
| 1613 |
|
|---|
| 1614 | You set the transforms you need later, either as flags to the high level
|
|---|
| 1615 | interface or libpng API calls for the low level interface. For reference the
|
|---|
| 1616 | settings and API calls required are:
|
|---|
| 1617 |
|
|---|
| 1618 | 8-bit values:
|
|---|
| 1619 | PNG_TRANSFORM_SCALE_16 | PNG_EXPAND
|
|---|
| 1620 | png_set_expand(png_ptr); png_set_scale_16(png_ptr);
|
|---|
| 1621 |
|
|---|
| 1622 | If you must get exactly the same inaccurate results
|
|---|
| 1623 | produced by default in versions prior to libpng-1.5.4,
|
|---|
| 1624 | use PNG_TRANSFORM_STRIP_16 and png_set_strip_16(png_ptr)
|
|---|
| 1625 | instead.
|
|---|
| 1626 |
|
|---|
| 1627 | 16-bit values:
|
|---|
| 1628 | PNG_TRANSFORM_EXPAND_16
|
|---|
| 1629 | png_set_expand_16(png_ptr);
|
|---|
| 1630 |
|
|---|
| 1631 | In either case palette image data will be expanded to RGB. If you just want
|
|---|
| 1632 | color data you can add PNG_TRANSFORM_GRAY_TO_RGB or png_set_gray_to_rgb(png_ptr)
|
|---|
| 1633 | to the list.
|
|---|
| 1634 |
|
|---|
| 1635 | Calling png_set_background before the PNG file header is read will not work
|
|---|
| 1636 | prior to libpng-1.5.4. Because the failure may result in unexpected warnings or
|
|---|
| 1637 | errors it is therefore much safer to call png_set_background after the head has
|
|---|
| 1638 | been read. Unfortunately this means that prior to libpng-1.5.4 it cannot be
|
|---|
| 1639 | used with the high level interface.
|
|---|
| 1640 |
|
|---|
| 1641 | .SS The high-level read interface
|
|---|
| 1642 |
|
|---|
| 1643 | At this point there are two ways to proceed; through the high-level
|
|---|
| 1644 | read interface, or through a sequence of low-level read operations.
|
|---|
| 1645 | You can use the high-level interface if (a) you are willing to read
|
|---|
| 1646 | the entire image into memory, and (b) the input transformations
|
|---|
| 1647 | you want to do are limited to the following set:
|
|---|
| 1648 |
|
|---|
| 1649 | PNG_TRANSFORM_IDENTITY No transformation
|
|---|
| 1650 | PNG_TRANSFORM_SCALE_16 Strip 16-bit samples to
|
|---|
| 1651 | 8-bit accurately
|
|---|
| 1652 | PNG_TRANSFORM_STRIP_16 Chop 16-bit samples to
|
|---|
| 1653 | 8-bit less accurately
|
|---|
| 1654 | PNG_TRANSFORM_STRIP_ALPHA Discard the alpha channel
|
|---|
| 1655 | PNG_TRANSFORM_PACKING Expand 1, 2 and 4-bit
|
|---|
| 1656 | samples to bytes
|
|---|
| 1657 | PNG_TRANSFORM_PACKSWAP Change order of packed
|
|---|
| 1658 | pixels to LSB first
|
|---|
| 1659 | PNG_TRANSFORM_EXPAND Perform set_expand()
|
|---|
| 1660 | PNG_TRANSFORM_INVERT_MONO Invert monochrome images
|
|---|
| 1661 | PNG_TRANSFORM_SHIFT Normalize pixels to the
|
|---|
| 1662 | sBIT depth
|
|---|
| 1663 | PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
|
|---|
| 1664 | to BGRA
|
|---|
| 1665 | PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
|
|---|
| 1666 | to AG
|
|---|
| 1667 | PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
|
|---|
| 1668 | to transparency
|
|---|
| 1669 | PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
|
|---|
| 1670 | PNG_TRANSFORM_GRAY_TO_RGB Expand grayscale samples
|
|---|
| 1671 | to RGB (or GA to RGBA)
|
|---|
| 1672 | PNG_TRANSFORM_EXPAND_16 Expand samples to 16 bits
|
|---|
| 1673 |
|
|---|
| 1674 | (This excludes setting a background color, doing gamma transformation,
|
|---|
| 1675 | quantizing, and setting filler.) If this is the case, simply do this:
|
|---|
| 1676 |
|
|---|
| 1677 | png_read_png(png_ptr, info_ptr, png_transforms, NULL)
|
|---|
| 1678 |
|
|---|
| 1679 | where png_transforms is an integer containing the bitwise OR of some
|
|---|
| 1680 | set of transformation flags. This call is equivalent to png_read_info(),
|
|---|
| 1681 | followed the set of transformations indicated by the transform mask,
|
|---|
| 1682 | then png_read_image(), and finally png_read_end().
|
|---|
| 1683 |
|
|---|
| 1684 | (The final parameter of this call is not yet used. Someday it might point
|
|---|
| 1685 | to transformation parameters required by some future input transform.)
|
|---|
| 1686 |
|
|---|
| 1687 | You must use png_transforms and not call any png_set_transform() functions
|
|---|
| 1688 | when you use png_read_png().
|
|---|
| 1689 |
|
|---|
| 1690 | After you have called png_read_png(), you can retrieve the image data
|
|---|
| 1691 | with
|
|---|
| 1692 |
|
|---|
| 1693 | row_pointers = png_get_rows(png_ptr, info_ptr);
|
|---|
| 1694 |
|
|---|
| 1695 | where row_pointers is an array of pointers to the pixel data for each row:
|
|---|
| 1696 |
|
|---|
| 1697 | png_bytep row_pointers[height];
|
|---|
| 1698 |
|
|---|
| 1699 | If you know your image size and pixel size ahead of time, you can allocate
|
|---|
| 1700 | row_pointers prior to calling png_read_png() with
|
|---|
| 1701 |
|
|---|
| 1702 | if (height > PNG_UINT_32_MAX/(sizeof (png_byte)))
|
|---|
| 1703 | png_error (png_ptr,
|
|---|
| 1704 | "Image is too tall to process in memory");
|
|---|
| 1705 |
|
|---|
| 1706 | if (width > PNG_UINT_32_MAX/pixel_size)
|
|---|
| 1707 | png_error (png_ptr,
|
|---|
| 1708 | "Image is too wide to process in memory");
|
|---|
| 1709 |
|
|---|
| 1710 | row_pointers = png_malloc(png_ptr,
|
|---|
| 1711 | height*(sizeof (png_bytep)));
|
|---|
| 1712 |
|
|---|
| 1713 | for (int i=0; i<height, i++)
|
|---|
| 1714 | row_pointers[i]=NULL; /* security precaution */
|
|---|
| 1715 |
|
|---|
| 1716 | for (int i=0; i<height, i++)
|
|---|
| 1717 | row_pointers[i]=png_malloc(png_ptr,
|
|---|
| 1718 | width*pixel_size);
|
|---|
| 1719 |
|
|---|
| 1720 | png_set_rows(png_ptr, info_ptr, &row_pointers);
|
|---|
| 1721 |
|
|---|
| 1722 | Alternatively you could allocate your image in one big block and define
|
|---|
| 1723 | row_pointers[i] to point into the proper places in your block, but first
|
|---|
| 1724 | be sure that your platform is able to allocate such a large buffer:
|
|---|
| 1725 |
|
|---|
| 1726 | /* Guard against integer overflow */
|
|---|
| 1727 | if (height > PNG_SIZE_MAX/(width*pixel_size)) {
|
|---|
| 1728 | png_error(png_ptr,"image_data buffer would be too large");
|
|---|
| 1729 | }
|
|---|
| 1730 |
|
|---|
| 1731 | png_bytep buffer=png_malloc(png_ptr,height*width*pixel_size);
|
|---|
| 1732 |
|
|---|
| 1733 | for (int i=0; i<height, i++)
|
|---|
| 1734 | row_pointers[i]=buffer+i*width*pixel_size;
|
|---|
| 1735 |
|
|---|
| 1736 | png_set_rows(png_ptr, info_ptr, &row_pointers);
|
|---|
| 1737 |
|
|---|
| 1738 | If you use png_set_rows(), the application is responsible for freeing
|
|---|
| 1739 | row_pointers (and row_pointers[i], if they were separately allocated).
|
|---|
| 1740 |
|
|---|
| 1741 | If you don't allocate row_pointers ahead of time, png_read_png() will
|
|---|
| 1742 | do it, and it'll be free'ed by libpng when you call png_destroy_*().
|
|---|
| 1743 |
|
|---|
| 1744 | .SS The low-level read interface
|
|---|
| 1745 |
|
|---|
| 1746 | If you are going the low-level route, you are now ready to read all
|
|---|
| 1747 | the file information up to the actual image data. You do this with a
|
|---|
| 1748 | call to png_read_info().
|
|---|
| 1749 |
|
|---|
| 1750 | png_read_info(png_ptr, info_ptr);
|
|---|
| 1751 |
|
|---|
| 1752 | This will process all chunks up to but not including the image data.
|
|---|
| 1753 |
|
|---|
| 1754 | This also copies some of the data from the PNG file into the decode structure
|
|---|
| 1755 | for use in later transformations. Important information copied in is:
|
|---|
| 1756 |
|
|---|
| 1757 | 1) The PNG file gamma from the gAMA chunk. This overwrites the default value
|
|---|
| 1758 | provided by an earlier call to png_set_gamma or png_set_alpha_mode.
|
|---|
| 1759 |
|
|---|
| 1760 | 2) Prior to libpng-1.5.4 the background color from a bKGd chunk. This
|
|---|
| 1761 | damages the information provided by an earlier call to png_set_background
|
|---|
| 1762 | resulting in unexpected behavior. Libpng-1.5.4 no longer does this.
|
|---|
| 1763 |
|
|---|
| 1764 | 3) The number of significant bits in each component value. Libpng uses this to
|
|---|
| 1765 | optimize gamma handling by reducing the internal lookup table sizes.
|
|---|
| 1766 |
|
|---|
| 1767 | 4) The transparent color information from a tRNS chunk. This can be modified by
|
|---|
| 1768 | a later call to png_set_tRNS.
|
|---|
| 1769 |
|
|---|
| 1770 | .SS Querying the info structure
|
|---|
| 1771 |
|
|---|
| 1772 | Functions are used to get the information from the info_ptr once it
|
|---|
| 1773 | has been read. Note that these fields may not be completely filled
|
|---|
| 1774 | in until png_read_end() has read the chunk data following the image.
|
|---|
| 1775 |
|
|---|
| 1776 | png_get_IHDR(png_ptr, info_ptr, &width, &height,
|
|---|
| 1777 | &bit_depth, &color_type, &interlace_type,
|
|---|
| 1778 | &compression_type, &filter_method);
|
|---|
| 1779 |
|
|---|
| 1780 | width - holds the width of the image
|
|---|
| 1781 | in pixels (up to 2^31).
|
|---|
| 1782 |
|
|---|
| 1783 | height - holds the height of the image
|
|---|
| 1784 | in pixels (up to 2^31).
|
|---|
| 1785 |
|
|---|
| 1786 | bit_depth - holds the bit depth of one of the
|
|---|
| 1787 | image channels. (valid values are
|
|---|
| 1788 | 1, 2, 4, 8, 16 and depend also on
|
|---|
| 1789 | the color_type. See also
|
|---|
| 1790 | significant bits (sBIT) below).
|
|---|
| 1791 |
|
|---|
| 1792 | color_type - describes which color/alpha channels
|
|---|
| 1793 | are present.
|
|---|
| 1794 | PNG_COLOR_TYPE_GRAY
|
|---|
| 1795 | (bit depths 1, 2, 4, 8, 16)
|
|---|
| 1796 | PNG_COLOR_TYPE_GRAY_ALPHA
|
|---|
| 1797 | (bit depths 8, 16)
|
|---|
| 1798 | PNG_COLOR_TYPE_PALETTE
|
|---|
| 1799 | (bit depths 1, 2, 4, 8)
|
|---|
| 1800 | PNG_COLOR_TYPE_RGB
|
|---|
| 1801 | (bit_depths 8, 16)
|
|---|
| 1802 | PNG_COLOR_TYPE_RGB_ALPHA
|
|---|
| 1803 | (bit_depths 8, 16)
|
|---|
| 1804 |
|
|---|
| 1805 | PNG_COLOR_MASK_PALETTE
|
|---|
| 1806 | PNG_COLOR_MASK_COLOR
|
|---|
| 1807 | PNG_COLOR_MASK_ALPHA
|
|---|
| 1808 |
|
|---|
| 1809 | interlace_type - (PNG_INTERLACE_NONE or
|
|---|
| 1810 | PNG_INTERLACE_ADAM7)
|
|---|
| 1811 |
|
|---|
| 1812 | compression_type - (must be PNG_COMPRESSION_TYPE_BASE
|
|---|
| 1813 | for PNG 1.0)
|
|---|
| 1814 |
|
|---|
| 1815 | filter_method - (must be PNG_FILTER_TYPE_BASE
|
|---|
| 1816 | for PNG 1.0, and can also be
|
|---|
| 1817 | PNG_INTRAPIXEL_DIFFERENCING if
|
|---|
| 1818 | the PNG datastream is embedded in
|
|---|
| 1819 | a MNG-1.0 datastream)
|
|---|
| 1820 |
|
|---|
| 1821 | Any of width, height, color_type, bit_depth,
|
|---|
| 1822 | interlace_type, compression_type, or filter_method can
|
|---|
| 1823 | be NULL if you are not interested in their values.
|
|---|
| 1824 |
|
|---|
| 1825 | Note that png_get_IHDR() returns 32-bit data into
|
|---|
| 1826 | the application's width and height variables.
|
|---|
| 1827 | This is an unsafe situation if these are not png_uint_32
|
|---|
| 1828 | variables. In such situations, the
|
|---|
| 1829 | png_get_image_width() and png_get_image_height()
|
|---|
| 1830 | functions described below are safer.
|
|---|
| 1831 |
|
|---|
| 1832 | width = png_get_image_width(png_ptr,
|
|---|
| 1833 | info_ptr);
|
|---|
| 1834 |
|
|---|
| 1835 | height = png_get_image_height(png_ptr,
|
|---|
| 1836 | info_ptr);
|
|---|
| 1837 |
|
|---|
| 1838 | bit_depth = png_get_bit_depth(png_ptr,
|
|---|
| 1839 | info_ptr);
|
|---|
| 1840 |
|
|---|
| 1841 | color_type = png_get_color_type(png_ptr,
|
|---|
| 1842 | info_ptr);
|
|---|
| 1843 |
|
|---|
| 1844 | interlace_type = png_get_interlace_type(png_ptr,
|
|---|
| 1845 | info_ptr);
|
|---|
| 1846 |
|
|---|
| 1847 | compression_type = png_get_compression_type(png_ptr,
|
|---|
| 1848 | info_ptr);
|
|---|
| 1849 |
|
|---|
| 1850 | filter_method = png_get_filter_type(png_ptr,
|
|---|
| 1851 | info_ptr);
|
|---|
| 1852 |
|
|---|
| 1853 | channels = png_get_channels(png_ptr, info_ptr);
|
|---|
| 1854 |
|
|---|
| 1855 | channels - number of channels of info for the
|
|---|
| 1856 | color type (valid values are 1 (GRAY,
|
|---|
| 1857 | PALETTE), 2 (GRAY_ALPHA), 3 (RGB),
|
|---|
| 1858 | 4 (RGB_ALPHA or RGB + filler byte))
|
|---|
| 1859 |
|
|---|
| 1860 | rowbytes = png_get_rowbytes(png_ptr, info_ptr);
|
|---|
| 1861 |
|
|---|
| 1862 | rowbytes - number of bytes needed to hold a row
|
|---|
| 1863 | This value, the bit_depth, color_type,
|
|---|
| 1864 | and the number of channels can change
|
|---|
| 1865 | if you use transforms such as
|
|---|
| 1866 | png_set_expand(). See
|
|---|
| 1867 | png_read_update_info(), below.
|
|---|
| 1868 |
|
|---|
| 1869 | signature = png_get_signature(png_ptr, info_ptr);
|
|---|
| 1870 |
|
|---|
| 1871 | signature - holds the signature read from the
|
|---|
| 1872 | file (if any). The data is kept in
|
|---|
| 1873 | the same offset it would be if the
|
|---|
| 1874 | whole signature were read (i.e. if an
|
|---|
| 1875 | application had already read in 4
|
|---|
| 1876 | bytes of signature before starting
|
|---|
| 1877 | libpng, the remaining 4 bytes would
|
|---|
| 1878 | be in signature[4] through signature[7]
|
|---|
| 1879 | (see png_set_sig_bytes())).
|
|---|
| 1880 |
|
|---|
| 1881 | These are also important, but their validity depends on whether the chunk
|
|---|
| 1882 | has been read. The png_get_valid(png_ptr, info_ptr, PNG_INFO_<chunk>) and
|
|---|
| 1883 | png_get_<chunk>(png_ptr, info_ptr, ...) functions return non-zero if the
|
|---|
| 1884 | data has been read, or zero if it is missing. The parameters to the
|
|---|
| 1885 | png_get_<chunk> are set directly if they are simple data types, or a
|
|---|
| 1886 | pointer into the info_ptr is returned for any complex types.
|
|---|
| 1887 |
|
|---|
| 1888 | The colorspace data from gAMA, cHRM, sRGB, iCCP, and sBIT chunks
|
|---|
| 1889 | is simply returned to give the application information about how the
|
|---|
| 1890 | image was encoded. Libpng itself only does transformations using the file
|
|---|
| 1891 | gamma when combining semitransparent pixels with the background color, and,
|
|---|
| 1892 | since libpng-1.6.0, when converting between 8-bit sRGB and 16-bit linear pixels
|
|---|
| 1893 | within the simplified API. Libpng also uses the file gamma when converting
|
|---|
| 1894 | RGB to gray, beginning with libpng-1.0.5, if the application calls
|
|---|
| 1895 | png_set_rgb_to_gray()).
|
|---|
| 1896 |
|
|---|
| 1897 | png_get_PLTE(png_ptr, info_ptr, &palette,
|
|---|
| 1898 | &num_palette);
|
|---|
| 1899 |
|
|---|
| 1900 | palette - the palette for the file
|
|---|
| 1901 | (array of png_color)
|
|---|
| 1902 |
|
|---|
| 1903 | num_palette - number of entries in the palette
|
|---|
| 1904 |
|
|---|
| 1905 | png_get_gAMA(png_ptr, info_ptr, &file_gamma);
|
|---|
| 1906 | png_get_gAMA_fixed(png_ptr, info_ptr, &int_file_gamma);
|
|---|
| 1907 |
|
|---|
| 1908 | file_gamma - the gamma at which the file is
|
|---|
| 1909 | written (PNG_INFO_gAMA)
|
|---|
| 1910 |
|
|---|
| 1911 | int_file_gamma - 100,000 times the gamma at which the
|
|---|
| 1912 | file is written
|
|---|
| 1913 |
|
|---|
| 1914 | png_get_cHRM(png_ptr, info_ptr, &white_x, &white_y, &red_x,
|
|---|
| 1915 | &red_y, &green_x, &green_y, &blue_x, &blue_y)
|
|---|
| 1916 | png_get_cHRM_XYZ(png_ptr, info_ptr, &red_X, &red_Y, &red_Z,
|
|---|
| 1917 | &green_X, &green_Y, &green_Z, &blue_X, &blue_Y,
|
|---|
| 1918 | &blue_Z)
|
|---|
| 1919 | png_get_cHRM_fixed(png_ptr, info_ptr, &int_white_x,
|
|---|
| 1920 | &int_white_y, &int_red_x, &int_red_y,
|
|---|
| 1921 | &int_green_x, &int_green_y, &int_blue_x,
|
|---|
| 1922 | &int_blue_y)
|
|---|
| 1923 | png_get_cHRM_XYZ_fixed(png_ptr, info_ptr, &int_red_X, &int_red_Y,
|
|---|
| 1924 | &int_red_Z, &int_green_X, &int_green_Y,
|
|---|
| 1925 | &int_green_Z, &int_blue_X, &int_blue_Y,
|
|---|
| 1926 | &int_blue_Z)
|
|---|
| 1927 |
|
|---|
| 1928 | {white,red,green,blue}_{x,y}
|
|---|
| 1929 | A color space encoding specified using the
|
|---|
| 1930 | chromaticities of the end points and the
|
|---|
| 1931 | white point. (PNG_INFO_cHRM)
|
|---|
| 1932 |
|
|---|
| 1933 | {red,green,blue}_{X,Y,Z}
|
|---|
| 1934 | A color space encoding specified using the
|
|---|
| 1935 | encoding end points - the CIE tristimulus
|
|---|
| 1936 | specification of the intended color of the red,
|
|---|
| 1937 | green and blue channels in the PNG RGB data.
|
|---|
| 1938 | The white point is simply the sum of the three
|
|---|
| 1939 | end points. (PNG_INFO_cHRM)
|
|---|
| 1940 |
|
|---|
| 1941 | png_get_sRGB(png_ptr, info_ptr, &srgb_intent);
|
|---|
| 1942 |
|
|---|
| 1943 | srgb_intent - the rendering intent (PNG_INFO_sRGB)
|
|---|
| 1944 | The presence of the sRGB chunk
|
|---|
| 1945 | means that the pixel data is in the
|
|---|
| 1946 | sRGB color space. This chunk also
|
|---|
| 1947 | implies specific values of gAMA and
|
|---|
| 1948 | cHRM.
|
|---|
| 1949 |
|
|---|
| 1950 | png_get_iCCP(png_ptr, info_ptr, &name,
|
|---|
| 1951 | &compression_type, &profile, &proflen);
|
|---|
| 1952 |
|
|---|
| 1953 | name - The profile name.
|
|---|
| 1954 |
|
|---|
| 1955 | compression_type - The compression type; always
|
|---|
| 1956 | PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
|
|---|
| 1957 | You may give NULL to this argument to
|
|---|
| 1958 | ignore it.
|
|---|
| 1959 |
|
|---|
| 1960 | profile - International Color Consortium color
|
|---|
| 1961 | profile data. May contain NULs.
|
|---|
| 1962 |
|
|---|
| 1963 | proflen - length of profile data in bytes.
|
|---|
| 1964 |
|
|---|
| 1965 | png_get_sBIT(png_ptr, info_ptr, &sig_bit);
|
|---|
| 1966 |
|
|---|
| 1967 | sig_bit - the number of significant bits for
|
|---|
| 1968 | (PNG_INFO_sBIT) each of the gray,
|
|---|
| 1969 | red, green, and blue channels,
|
|---|
| 1970 | whichever are appropriate for the
|
|---|
| 1971 | given color type (png_color_16)
|
|---|
| 1972 |
|
|---|
| 1973 | png_get_tRNS(png_ptr, info_ptr, &trans_alpha,
|
|---|
| 1974 | &num_trans, &trans_color);
|
|---|
| 1975 |
|
|---|
| 1976 | trans_alpha - array of alpha (transparency)
|
|---|
| 1977 | entries for palette (PNG_INFO_tRNS)
|
|---|
| 1978 |
|
|---|
| 1979 | num_trans - number of transparent entries
|
|---|
| 1980 | (PNG_INFO_tRNS)
|
|---|
| 1981 |
|
|---|
| 1982 | trans_color - graylevel or color sample values of
|
|---|
| 1983 | the single transparent color for
|
|---|
| 1984 | non-paletted images (PNG_INFO_tRNS)
|
|---|
| 1985 |
|
|---|
| 1986 | png_get_eXIf_1(png_ptr, info_ptr, &num_exif, &exif);
|
|---|
| 1987 | (PNG_INFO_eXIf)
|
|---|
| 1988 |
|
|---|
| 1989 | exif - Exif profile (array of png_byte)
|
|---|
| 1990 |
|
|---|
| 1991 | png_get_hIST(png_ptr, info_ptr, &hist);
|
|---|
| 1992 | (PNG_INFO_hIST)
|
|---|
| 1993 |
|
|---|
| 1994 | hist - histogram of palette (array of
|
|---|
| 1995 | png_uint_16)
|
|---|
| 1996 |
|
|---|
| 1997 | png_get_tIME(png_ptr, info_ptr, &mod_time);
|
|---|
| 1998 |
|
|---|
| 1999 | mod_time - time image was last modified
|
|---|
| 2000 | (PNG_VALID_tIME)
|
|---|
| 2001 |
|
|---|
| 2002 | png_get_bKGD(png_ptr, info_ptr, &background);
|
|---|
| 2003 |
|
|---|
| 2004 | background - background color (of type
|
|---|
| 2005 | png_color_16p) (PNG_VALID_bKGD)
|
|---|
| 2006 | valid 16-bit red, green and blue
|
|---|
| 2007 | values, regardless of color_type
|
|---|
| 2008 |
|
|---|
| 2009 | num_comments = png_get_text(png_ptr, info_ptr,
|
|---|
| 2010 | &text_ptr, &num_text);
|
|---|
| 2011 |
|
|---|
| 2012 | num_comments - number of comments
|
|---|
| 2013 |
|
|---|
| 2014 | text_ptr - array of png_text holding image
|
|---|
| 2015 | comments
|
|---|
| 2016 |
|
|---|
| 2017 | text_ptr[i].compression - type of compression used
|
|---|
| 2018 | on "text" PNG_TEXT_COMPRESSION_NONE
|
|---|
| 2019 | PNG_TEXT_COMPRESSION_zTXt
|
|---|
| 2020 | PNG_ITXT_COMPRESSION_NONE
|
|---|
| 2021 | PNG_ITXT_COMPRESSION_zTXt
|
|---|
| 2022 |
|
|---|
| 2023 | text_ptr[i].key - keyword for comment. Must contain
|
|---|
| 2024 | 1-79 characters.
|
|---|
| 2025 |
|
|---|
| 2026 | text_ptr[i].text - text comments for current
|
|---|
| 2027 | keyword. Can be empty.
|
|---|
| 2028 |
|
|---|
| 2029 | text_ptr[i].text_length - length of text string,
|
|---|
| 2030 | after decompression, 0 for iTXt
|
|---|
| 2031 |
|
|---|
| 2032 | text_ptr[i].itxt_length - length of itxt string,
|
|---|
| 2033 | after decompression, 0 for tEXt/zTXt
|
|---|
| 2034 |
|
|---|
| 2035 | text_ptr[i].lang - language of comment (empty
|
|---|
| 2036 | string for unknown).
|
|---|
| 2037 |
|
|---|
| 2038 | text_ptr[i].lang_key - keyword in UTF-8
|
|---|
| 2039 | (empty string for unknown).
|
|---|
| 2040 |
|
|---|
| 2041 | Note that the itxt_length, lang, and lang_key
|
|---|
| 2042 | members of the text_ptr structure only exist when the
|
|---|
| 2043 | library is built with iTXt chunk support. Prior to
|
|---|
| 2044 | libpng-1.4.0 the library was built by default without
|
|---|
| 2045 | iTXt support. Also note that when iTXt is supported,
|
|---|
| 2046 | they contain NULL pointers when the "compression"
|
|---|
| 2047 | field contains PNG_TEXT_COMPRESSION_NONE or
|
|---|
| 2048 | PNG_TEXT_COMPRESSION_zTXt.
|
|---|
| 2049 |
|
|---|
| 2050 | num_text - number of comments (same as
|
|---|
| 2051 | num_comments; you can put NULL here
|
|---|
| 2052 | to avoid the duplication)
|
|---|
| 2053 |
|
|---|
| 2054 | Note while png_set_text() will accept text, language,
|
|---|
| 2055 | and translated keywords that can be NULL pointers, the
|
|---|
| 2056 | structure returned by png_get_text will always contain
|
|---|
| 2057 | regular zero-terminated C strings. They might be
|
|---|
| 2058 | empty strings but they will never be NULL pointers.
|
|---|
| 2059 |
|
|---|
| 2060 | num_spalettes = png_get_sPLT(png_ptr, info_ptr,
|
|---|
| 2061 | &palette_ptr);
|
|---|
| 2062 |
|
|---|
| 2063 | num_spalettes - number of sPLT chunks read.
|
|---|
| 2064 |
|
|---|
| 2065 | palette_ptr - array of palette structures holding
|
|---|
| 2066 | contents of one or more sPLT chunks
|
|---|
| 2067 | read.
|
|---|
| 2068 |
|
|---|
| 2069 | png_get_oFFs(png_ptr, info_ptr, &offset_x, &offset_y,
|
|---|
| 2070 | &unit_type);
|
|---|
| 2071 |
|
|---|
| 2072 | offset_x - positive offset from the left edge
|
|---|
| 2073 | of the screen (can be negative)
|
|---|
| 2074 |
|
|---|
| 2075 | offset_y - positive offset from the top edge
|
|---|
| 2076 | of the screen (can be negative)
|
|---|
| 2077 |
|
|---|
| 2078 | unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
|
|---|
| 2079 |
|
|---|
| 2080 | png_get_pHYs(png_ptr, info_ptr, &res_x, &res_y,
|
|---|
| 2081 | &unit_type);
|
|---|
| 2082 |
|
|---|
| 2083 | res_x - pixels/unit physical resolution in
|
|---|
| 2084 | x direction
|
|---|
| 2085 |
|
|---|
| 2086 | res_y - pixels/unit physical resolution in
|
|---|
| 2087 | x direction
|
|---|
| 2088 |
|
|---|
| 2089 | unit_type - PNG_RESOLUTION_UNKNOWN,
|
|---|
| 2090 | PNG_RESOLUTION_METER
|
|---|
| 2091 |
|
|---|
| 2092 | png_get_sCAL(png_ptr, info_ptr, &unit, &width,
|
|---|
| 2093 | &height)
|
|---|
| 2094 |
|
|---|
| 2095 | unit - physical scale units (an integer)
|
|---|
| 2096 |
|
|---|
| 2097 | width - width of a pixel in physical scale units
|
|---|
| 2098 |
|
|---|
| 2099 | height - height of a pixel in physical scale units
|
|---|
| 2100 | (width and height are doubles)
|
|---|
| 2101 |
|
|---|
| 2102 | png_get_sCAL_s(png_ptr, info_ptr, &unit, &width,
|
|---|
| 2103 | &height)
|
|---|
| 2104 |
|
|---|
| 2105 | unit - physical scale units (an integer)
|
|---|
| 2106 |
|
|---|
| 2107 | width - width of a pixel in physical scale units
|
|---|
| 2108 | (expressed as a string)
|
|---|
| 2109 |
|
|---|
| 2110 | height - height of a pixel in physical scale units
|
|---|
| 2111 | (width and height are strings like "2.54")
|
|---|
| 2112 |
|
|---|
| 2113 | num_unknown_chunks = png_get_unknown_chunks(png_ptr,
|
|---|
| 2114 | info_ptr, &unknowns)
|
|---|
| 2115 |
|
|---|
| 2116 | unknowns - array of png_unknown_chunk
|
|---|
| 2117 | structures holding unknown chunks
|
|---|
| 2118 |
|
|---|
| 2119 | unknowns[i].name - name of unknown chunk
|
|---|
| 2120 |
|
|---|
| 2121 | unknowns[i].data - data of unknown chunk
|
|---|
| 2122 |
|
|---|
| 2123 | unknowns[i].size - size of unknown chunk's data
|
|---|
| 2124 |
|
|---|
| 2125 | unknowns[i].location - position of chunk in file
|
|---|
| 2126 |
|
|---|
| 2127 | The value of "i" corresponds to the order in which the
|
|---|
| 2128 | chunks were read from the PNG file or inserted with the
|
|---|
| 2129 | png_set_unknown_chunks() function.
|
|---|
| 2130 |
|
|---|
| 2131 | The value of "location" is a bitwise "or" of
|
|---|
| 2132 |
|
|---|
| 2133 | PNG_HAVE_IHDR (0x01)
|
|---|
| 2134 | PNG_HAVE_PLTE (0x02)
|
|---|
| 2135 | PNG_AFTER_IDAT (0x08)
|
|---|
| 2136 |
|
|---|
| 2137 | The data from the pHYs chunk can be retrieved in several convenient
|
|---|
| 2138 | forms:
|
|---|
| 2139 |
|
|---|
| 2140 | res_x = png_get_x_pixels_per_meter(png_ptr,
|
|---|
| 2141 | info_ptr)
|
|---|
| 2142 |
|
|---|
| 2143 | res_y = png_get_y_pixels_per_meter(png_ptr,
|
|---|
| 2144 | info_ptr)
|
|---|
| 2145 |
|
|---|
| 2146 | res_x_and_y = png_get_pixels_per_meter(png_ptr,
|
|---|
| 2147 | info_ptr)
|
|---|
| 2148 |
|
|---|
| 2149 | res_x = png_get_x_pixels_per_inch(png_ptr,
|
|---|
| 2150 | info_ptr)
|
|---|
| 2151 |
|
|---|
| 2152 | res_y = png_get_y_pixels_per_inch(png_ptr,
|
|---|
| 2153 | info_ptr)
|
|---|
| 2154 |
|
|---|
| 2155 | res_x_and_y = png_get_pixels_per_inch(png_ptr,
|
|---|
| 2156 | info_ptr)
|
|---|
| 2157 |
|
|---|
| 2158 | aspect_ratio = png_get_pixel_aspect_ratio(png_ptr,
|
|---|
| 2159 | info_ptr)
|
|---|
| 2160 |
|
|---|
| 2161 | Each of these returns 0 [signifying "unknown"] if
|
|---|
| 2162 | the data is not present or if res_x is 0;
|
|---|
| 2163 | res_x_and_y is 0 if res_x != res_y
|
|---|
| 2164 |
|
|---|
| 2165 | Note that because of the way the resolutions are
|
|---|
| 2166 | stored internally, the inch conversions won't
|
|---|
| 2167 | come out to exactly even number. For example,
|
|---|
| 2168 | 72 dpi is stored as 0.28346 pixels/meter, and
|
|---|
| 2169 | when this is retrieved it is 71.9988 dpi, so
|
|---|
| 2170 | be sure to round the returned value appropriately
|
|---|
| 2171 | if you want to display a reasonable-looking result.
|
|---|
| 2172 |
|
|---|
| 2173 | The data from the oFFs chunk can be retrieved in several convenient
|
|---|
| 2174 | forms:
|
|---|
| 2175 |
|
|---|
| 2176 | x_offset = png_get_x_offset_microns(png_ptr, info_ptr);
|
|---|
| 2177 |
|
|---|
| 2178 | y_offset = png_get_y_offset_microns(png_ptr, info_ptr);
|
|---|
| 2179 |
|
|---|
| 2180 | x_offset = png_get_x_offset_inches(png_ptr, info_ptr);
|
|---|
| 2181 |
|
|---|
| 2182 | y_offset = png_get_y_offset_inches(png_ptr, info_ptr);
|
|---|
| 2183 |
|
|---|
| 2184 | Each of these returns 0 [signifying "unknown" if both
|
|---|
| 2185 | x and y are 0] if the data is not present or if the
|
|---|
| 2186 | chunk is present but the unit is the pixel. The
|
|---|
| 2187 | remark about inexact inch conversions applies here
|
|---|
| 2188 | as well, because a value in inches can't always be
|
|---|
| 2189 | converted to microns and back without some loss
|
|---|
| 2190 | of precision.
|
|---|
| 2191 |
|
|---|
| 2192 | For more information, see the
|
|---|
| 2193 | PNG specification for chunk contents. Be careful with trusting
|
|---|
| 2194 | rowbytes, as some of the transformations could increase the space
|
|---|
| 2195 | needed to hold a row (expand, filler, gray_to_rgb, etc.).
|
|---|
| 2196 | See png_read_update_info(), below.
|
|---|
| 2197 |
|
|---|
| 2198 | A quick word about text_ptr and num_text. PNG stores comments in
|
|---|
| 2199 | keyword/text pairs, one pair per chunk, with no limit on the number
|
|---|
| 2200 | of text chunks, and a 2^31 byte limit on their size. While there are
|
|---|
| 2201 | suggested keywords, there is no requirement to restrict the use to these
|
|---|
| 2202 | strings. It is strongly suggested that keywords and text be sensible
|
|---|
| 2203 | to humans (that's the point), so don't use abbreviations. Non-printing
|
|---|
| 2204 | symbols are not allowed. See the PNG specification for more details.
|
|---|
| 2205 | There is also no requirement to have text after the keyword.
|
|---|
| 2206 |
|
|---|
| 2207 | Keywords should be limited to 79 Latin-1 characters without leading or
|
|---|
| 2208 | trailing spaces, but non-consecutive spaces are allowed within the
|
|---|
| 2209 | keyword. It is possible to have the same keyword any number of times.
|
|---|
| 2210 | The text_ptr is an array of png_text structures, each holding a
|
|---|
| 2211 | pointer to a language string, a pointer to a keyword and a pointer to
|
|---|
| 2212 | a text string. The text string, language code, and translated
|
|---|
| 2213 | keyword may be empty or NULL pointers. The keyword/text
|
|---|
| 2214 | pairs are put into the array in the order that they are received.
|
|---|
| 2215 | However, some or all of the text chunks may be after the image, so, to
|
|---|
| 2216 | make sure you have read all the text chunks, don't mess with these
|
|---|
| 2217 | until after you read the stuff after the image. This will be
|
|---|
| 2218 | mentioned again below in the discussion that goes with png_read_end().
|
|---|
| 2219 |
|
|---|
| 2220 | .SS Input transformations
|
|---|
| 2221 |
|
|---|
| 2222 | After you've read the header information, you can set up the library
|
|---|
| 2223 | to handle any special transformations of the image data. The various
|
|---|
| 2224 | ways to transform the data will be described in the order that they
|
|---|
| 2225 | should occur. This is important, as some of these change the color
|
|---|
| 2226 | type and/or bit depth of the data, and some others only work on
|
|---|
| 2227 | certain color types and bit depths.
|
|---|
| 2228 |
|
|---|
| 2229 | Transformations you request are ignored if they don't have any meaning for a
|
|---|
| 2230 | particular input data format. However some transformations can have an effect
|
|---|
| 2231 | as a result of a previous transformation. If you specify a contradictory set of
|
|---|
| 2232 | transformations, for example both adding and removing the alpha channel, you
|
|---|
| 2233 | cannot predict the final result.
|
|---|
| 2234 |
|
|---|
| 2235 | The color used for the transparency values should be supplied in the same
|
|---|
| 2236 | format/depth as the current image data. It is stored in the same format/depth
|
|---|
| 2237 | as the image data in a tRNS chunk, so this is what libpng expects for this data.
|
|---|
| 2238 |
|
|---|
| 2239 | The color used for the background value depends on the need_expand argument as
|
|---|
| 2240 | described below.
|
|---|
| 2241 |
|
|---|
| 2242 | Data will be decoded into the supplied row buffers packed into bytes
|
|---|
| 2243 | unless the library has been told to transform it into another format.
|
|---|
| 2244 | For example, 4 bit/pixel paletted or grayscale data will be returned
|
|---|
| 2245 | 2 pixels/byte with the leftmost pixel in the high-order bits of the byte,
|
|---|
| 2246 | unless png_set_packing() is called. 8-bit RGB data will be stored
|
|---|
| 2247 | in RGB RGB RGB format unless png_set_filler() or png_set_add_alpha()
|
|---|
| 2248 | is called to insert filler bytes, either before or after each RGB triplet.
|
|---|
| 2249 |
|
|---|
| 2250 | 16-bit RGB data will be returned RRGGBB RRGGBB, with the most significant
|
|---|
| 2251 | byte of the color value first, unless png_set_scale_16() is called to
|
|---|
| 2252 | transform it to regular RGB RGB triplets, or png_set_filler() or
|
|---|
| 2253 | png_set_add alpha() is called to insert two filler bytes, either before
|
|---|
| 2254 | or after each RRGGBB triplet. Similarly, 8-bit or 16-bit grayscale data can
|
|---|
| 2255 | be modified with png_set_filler(), png_set_add_alpha(), png_set_strip_16(),
|
|---|
| 2256 | or png_set_scale_16().
|
|---|
| 2257 |
|
|---|
| 2258 | The following code transforms grayscale images of less than 8 to 8 bits,
|
|---|
| 2259 | changes paletted images to RGB, and adds a full alpha channel if there is
|
|---|
| 2260 | transparency information in a tRNS chunk. This is most useful on
|
|---|
| 2261 | grayscale images with bit depths of 2 or 4 or if there is a multiple-image
|
|---|
| 2262 | viewing application that wishes to treat all images in the same way.
|
|---|
| 2263 |
|
|---|
| 2264 | if (color_type == PNG_COLOR_TYPE_PALETTE)
|
|---|
| 2265 | png_set_palette_to_rgb(png_ptr);
|
|---|
| 2266 |
|
|---|
| 2267 | if (png_get_valid(png_ptr, info_ptr,
|
|---|
| 2268 | PNG_INFO_tRNS)) png_set_tRNS_to_alpha(png_ptr);
|
|---|
| 2269 |
|
|---|
| 2270 | if (color_type == PNG_COLOR_TYPE_GRAY &&
|
|---|
| 2271 | bit_depth < 8) png_set_expand_gray_1_2_4_to_8(png_ptr);
|
|---|
| 2272 |
|
|---|
| 2273 | The first two functions are actually aliases for png_set_expand(), added
|
|---|
| 2274 | in libpng version 1.0.4, with the function names expanded to improve code
|
|---|
| 2275 | readability. In some future version they may actually do different
|
|---|
| 2276 | things.
|
|---|
| 2277 |
|
|---|
| 2278 | As of libpng version 1.2.9, png_set_expand_gray_1_2_4_to_8() was
|
|---|
| 2279 | added. It expands the sample depth without changing tRNS to alpha.
|
|---|
| 2280 |
|
|---|
| 2281 | As of libpng version 1.5.2, png_set_expand_16() was added. It behaves as
|
|---|
| 2282 | png_set_expand(); however, the resultant channels have 16 bits rather than 8.
|
|---|
| 2283 | Use this when the output color or gray channels are made linear to avoid fairly
|
|---|
| 2284 | severe accuracy loss.
|
|---|
| 2285 |
|
|---|
| 2286 | if (bit_depth < 16)
|
|---|
| 2287 | png_set_expand_16(png_ptr);
|
|---|
| 2288 |
|
|---|
| 2289 | PNG can have files with 16 bits per channel. If you only can handle
|
|---|
| 2290 | 8 bits per channel, this will strip the pixels down to 8-bit.
|
|---|
| 2291 |
|
|---|
| 2292 | if (bit_depth == 16)
|
|---|
| 2293 | #if PNG_LIBPNG_VER >= 10504
|
|---|
| 2294 | png_set_scale_16(png_ptr);
|
|---|
| 2295 | #else
|
|---|
| 2296 | png_set_strip_16(png_ptr);
|
|---|
| 2297 | #endif
|
|---|
| 2298 |
|
|---|
| 2299 | (The more accurate "png_set_scale_16()" API became available in libpng version
|
|---|
| 2300 | 1.5.4).
|
|---|
| 2301 |
|
|---|
| 2302 | If you need to process the alpha channel on the image separately from the image
|
|---|
| 2303 | data (for example if you convert it to a bitmap mask) it is possible to have
|
|---|
| 2304 | libpng strip the channel leaving just RGB or gray data:
|
|---|
| 2305 |
|
|---|
| 2306 | if (color_type & PNG_COLOR_MASK_ALPHA)
|
|---|
| 2307 | png_set_strip_alpha(png_ptr);
|
|---|
| 2308 |
|
|---|
| 2309 | If you strip the alpha channel you need to find some other way of dealing with
|
|---|
| 2310 | the information. If, instead, you want to convert the image to an opaque
|
|---|
| 2311 | version with no alpha channel use png_set_background; see below.
|
|---|
| 2312 |
|
|---|
| 2313 | As of libpng version 1.5.2, almost all useful expansions are supported, the
|
|---|
| 2314 | major ommissions are conversion of grayscale to indexed images (which can be
|
|---|
| 2315 | done trivially in the application) and conversion of indexed to grayscale (which
|
|---|
| 2316 | can be done by a trivial manipulation of the palette.)
|
|---|
| 2317 |
|
|---|
| 2318 | In the following table, the 01 means grayscale with depth<8, 31 means
|
|---|
| 2319 | indexed with depth<8, other numerals represent the color type, "T" means
|
|---|
| 2320 | the tRNS chunk is present, A means an alpha channel is present, and O
|
|---|
| 2321 | means tRNS or alpha is present but all pixels in the image are opaque.
|
|---|
| 2322 |
|
|---|
| 2323 | FROM 01 31 0 0T 0O 2 2T 2O 3 3T 3O 4A 4O 6A 6O
|
|---|
| 2324 | TO
|
|---|
| 2325 | 01 - [G] - - - - - - - - - - - - -
|
|---|
| 2326 | 31 [Q] Q [Q] [Q] [Q] Q Q Q Q Q Q [Q] [Q] Q Q
|
|---|
| 2327 | 0 1 G + . . G G G G G G B B GB GB
|
|---|
| 2328 | 0T lt Gt t + . Gt G G Gt G G Bt Bt GBt GBt
|
|---|
| 2329 | 0O lt Gt t . + Gt Gt G Gt Gt G Bt Bt GBt GBt
|
|---|
| 2330 | 2 C P C C C + . . C - - CB CB B B
|
|---|
| 2331 | 2T Ct - Ct C C t + t - - - CBt CBt Bt Bt
|
|---|
| 2332 | 2O Ct - Ct C C t t + - - - CBt CBt Bt Bt
|
|---|
| 2333 | 3 [Q] p [Q] [Q] [Q] Q Q Q + . . [Q] [Q] Q Q
|
|---|
| 2334 | 3T [Qt] p [Qt][Q] [Q] Qt Qt Qt t + t [Qt][Qt] Qt Qt
|
|---|
| 2335 | 3O [Qt] p [Qt][Q] [Q] Qt Qt Qt t t + [Qt][Qt] Qt Qt
|
|---|
| 2336 | 4A lA G A T T GA GT GT GA GT GT + BA G GBA
|
|---|
| 2337 | 4O lA GBA A T T GA GT GT GA GT GT BA + GBA G
|
|---|
| 2338 | 6A CA PA CA C C A T tT PA P P C CBA + BA
|
|---|
| 2339 | 6O CA PBA CA C C A tT T PA P P CBA C BA +
|
|---|
| 2340 |
|
|---|
| 2341 | Within the matrix,
|
|---|
| 2342 | "+" identifies entries where 'from' and 'to' are the same.
|
|---|
| 2343 | "-" means the transformation is not supported.
|
|---|
| 2344 | "." means nothing is necessary (a tRNS chunk can just be ignored).
|
|---|
| 2345 | "t" means the transformation is obtained by png_set_tRNS.
|
|---|
| 2346 | "A" means the transformation is obtained by png_set_add_alpha().
|
|---|
| 2347 | "X" means the transformation is obtained by png_set_expand().
|
|---|
| 2348 | "1" means the transformation is obtained by
|
|---|
| 2349 | png_set_expand_gray_1_2_4_to_8() (and by png_set_expand()
|
|---|
| 2350 | if there is no transparency in the original or the final
|
|---|
| 2351 | format).
|
|---|
| 2352 | "C" means the transformation is obtained by png_set_gray_to_rgb().
|
|---|
| 2353 | "G" means the transformation is obtained by png_set_rgb_to_gray().
|
|---|
| 2354 | "P" means the transformation is obtained by
|
|---|
| 2355 | png_set_expand_palette_to_rgb().
|
|---|
| 2356 | "p" means the transformation is obtained by png_set_packing().
|
|---|
| 2357 | "Q" means the transformation is obtained by png_set_quantize().
|
|---|
| 2358 | "T" means the transformation is obtained by
|
|---|
| 2359 | png_set_tRNS_to_alpha().
|
|---|
| 2360 | "B" means the transformation is obtained by
|
|---|
| 2361 | png_set_background(), or png_strip_alpha().
|
|---|
| 2362 |
|
|---|
| 2363 | When an entry has multiple transforms listed all are required to cause the
|
|---|
| 2364 | right overall transformation. When two transforms are separated by a comma
|
|---|
| 2365 | either will do the job. When transforms are enclosed in [] the transform should
|
|---|
| 2366 | do the job but this is currently unimplemented - a different format will result
|
|---|
| 2367 | if the suggested transformations are used.
|
|---|
| 2368 |
|
|---|
| 2369 | In PNG files, the alpha channel in an image
|
|---|
| 2370 | is the level of opacity. If you need the alpha channel in an image to
|
|---|
| 2371 | be the level of transparency instead of opacity, you can invert the
|
|---|
| 2372 | alpha channel (or the tRNS chunk data) after it's read, so that 0 is
|
|---|
| 2373 | fully opaque and 255 (in 8-bit or paletted images) or 65535 (in 16-bit
|
|---|
| 2374 | images) is fully transparent, with
|
|---|
| 2375 |
|
|---|
| 2376 | png_set_invert_alpha(png_ptr);
|
|---|
| 2377 |
|
|---|
| 2378 | PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
|
|---|
| 2379 | they can, resulting in, for example, 8 pixels per byte for 1 bit
|
|---|
| 2380 | files. This code expands to 1 pixel per byte without changing the
|
|---|
| 2381 | values of the pixels:
|
|---|
| 2382 |
|
|---|
| 2383 | if (bit_depth < 8)
|
|---|
| 2384 | png_set_packing(png_ptr);
|
|---|
| 2385 |
|
|---|
| 2386 | PNG files have possible bit depths of 1, 2, 4, 8, and 16. All pixels
|
|---|
| 2387 | stored in a PNG image have been "scaled" or "shifted" up to the next
|
|---|
| 2388 | higher possible bit depth (e.g. from 5 bits/sample in the range [0,31]
|
|---|
| 2389 | to 8 bits/sample in the range [0, 255]). However, it is also possible
|
|---|
| 2390 | to convert the PNG pixel data back to the original bit depth of the
|
|---|
| 2391 | image. This call reduces the pixels back down to the original bit depth:
|
|---|
| 2392 |
|
|---|
| 2393 | png_color_8p sig_bit;
|
|---|
| 2394 |
|
|---|
| 2395 | if (png_get_sBIT(png_ptr, info_ptr, &sig_bit))
|
|---|
| 2396 | png_set_shift(png_ptr, sig_bit);
|
|---|
| 2397 |
|
|---|
| 2398 | PNG files store 3-color pixels in red, green, blue order. This code
|
|---|
| 2399 | changes the storage of the pixels to blue, green, red:
|
|---|
| 2400 |
|
|---|
| 2401 | if (color_type == PNG_COLOR_TYPE_RGB ||
|
|---|
| 2402 | color_type == PNG_COLOR_TYPE_RGB_ALPHA)
|
|---|
| 2403 | png_set_bgr(png_ptr);
|
|---|
| 2404 |
|
|---|
| 2405 | PNG files store RGB pixels packed into 3 or 6 bytes. This code expands them
|
|---|
| 2406 | into 4 or 8 bytes for windowing systems that need them in this format:
|
|---|
| 2407 |
|
|---|
| 2408 | if (color_type == PNG_COLOR_TYPE_RGB)
|
|---|
| 2409 | png_set_filler(png_ptr, filler, PNG_FILLER_BEFORE);
|
|---|
| 2410 |
|
|---|
| 2411 | where "filler" is the 8-bit or 16-bit number to fill with, and the location
|
|---|
| 2412 | is either PNG_FILLER_BEFORE or PNG_FILLER_AFTER, depending upon whether
|
|---|
| 2413 | you want the filler before the RGB or after. When filling an 8-bit pixel,
|
|---|
| 2414 | the least significant 8 bits of the number are used, if a 16-bit number is
|
|---|
| 2415 | supplied. This transformation does not affect images that already have full
|
|---|
| 2416 | alpha channels. To add an opaque alpha channel, use filler=0xffff and
|
|---|
| 2417 | PNG_FILLER_AFTER which will generate RGBA pixels.
|
|---|
| 2418 |
|
|---|
| 2419 | Note that png_set_filler() does not change the color type. If you want
|
|---|
| 2420 | to do that, you can add a true alpha channel with
|
|---|
| 2421 |
|
|---|
| 2422 | if (color_type == PNG_COLOR_TYPE_RGB ||
|
|---|
| 2423 | color_type == PNG_COLOR_TYPE_GRAY)
|
|---|
| 2424 | png_set_add_alpha(png_ptr, filler, PNG_FILLER_AFTER);
|
|---|
| 2425 |
|
|---|
| 2426 | where "filler" contains the alpha value to assign to each pixel.
|
|---|
| 2427 | The png_set_add_alpha() function was added in libpng-1.2.7.
|
|---|
| 2428 |
|
|---|
| 2429 | If you are reading an image with an alpha channel, and you need the
|
|---|
| 2430 | data as ARGB instead of the normal PNG format RGBA:
|
|---|
| 2431 |
|
|---|
| 2432 | if (color_type == PNG_COLOR_TYPE_RGB_ALPHA)
|
|---|
| 2433 | png_set_swap_alpha(png_ptr);
|
|---|
| 2434 |
|
|---|
| 2435 | For some uses, you may want a grayscale image to be represented as
|
|---|
| 2436 | RGB. This code will do that conversion:
|
|---|
| 2437 |
|
|---|
| 2438 | if (color_type == PNG_COLOR_TYPE_GRAY ||
|
|---|
| 2439 | color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
|
|---|
| 2440 | png_set_gray_to_rgb(png_ptr);
|
|---|
| 2441 |
|
|---|
| 2442 | Conversely, you can convert an RGB or RGBA image to grayscale or grayscale
|
|---|
| 2443 | with alpha.
|
|---|
| 2444 |
|
|---|
| 2445 | if (color_type == PNG_COLOR_TYPE_RGB ||
|
|---|
| 2446 | color_type == PNG_COLOR_TYPE_RGB_ALPHA)
|
|---|
| 2447 | png_set_rgb_to_gray(png_ptr, error_action,
|
|---|
| 2448 | double red_weight, double green_weight);
|
|---|
| 2449 |
|
|---|
| 2450 | error_action = 1: silently do the conversion
|
|---|
| 2451 |
|
|---|
| 2452 | error_action = 2: issue a warning if the original
|
|---|
| 2453 | image has any pixel where
|
|---|
| 2454 | red != green or red != blue
|
|---|
| 2455 |
|
|---|
| 2456 | error_action = 3: issue an error and abort the
|
|---|
| 2457 | conversion if the original
|
|---|
| 2458 | image has any pixel where
|
|---|
| 2459 | red != green or red != blue
|
|---|
| 2460 |
|
|---|
| 2461 | red_weight: weight of red component
|
|---|
| 2462 |
|
|---|
| 2463 | green_weight: weight of green component
|
|---|
| 2464 | If either weight is negative, default
|
|---|
| 2465 | weights are used.
|
|---|
| 2466 |
|
|---|
| 2467 | In the corresponding fixed point API the red_weight and green_weight values are
|
|---|
| 2468 | simply scaled by 100,000:
|
|---|
| 2469 |
|
|---|
| 2470 | png_set_rgb_to_gray(png_ptr, error_action,
|
|---|
| 2471 | png_fixed_point red_weight,
|
|---|
| 2472 | png_fixed_point green_weight);
|
|---|
| 2473 |
|
|---|
| 2474 | If you have set error_action = 1 or 2, you can
|
|---|
| 2475 | later check whether the image really was gray, after processing
|
|---|
| 2476 | the image rows, with the png_get_rgb_to_gray_status(png_ptr) function.
|
|---|
| 2477 | It will return a png_byte that is zero if the image was gray or
|
|---|
| 2478 | 1 if there were any non-gray pixels. Background and sBIT data
|
|---|
| 2479 | will be silently converted to grayscale, using the green channel
|
|---|
| 2480 | data for sBIT, regardless of the error_action setting.
|
|---|
| 2481 |
|
|---|
| 2482 | The default values come from the PNG file cHRM chunk if present; otherwise, the
|
|---|
| 2483 | defaults correspond to the ITU-R recommendation 709, and also the sRGB color
|
|---|
| 2484 | space, as recommended in the Charles Poynton's Colour FAQ,
|
|---|
| 2485 | Copyright (c) 2006-11-28 Charles Poynton, in section 9:
|
|---|
| 2486 |
|
|---|
| 2487 | <http://www.poynton.com/notes/colour_and_gamma/ColorFAQ.html#RTFToC9>
|
|---|
| 2488 |
|
|---|
| 2489 | Y = 0.2126 * R + 0.7152 * G + 0.0722 * B
|
|---|
| 2490 |
|
|---|
| 2491 | Previous versions of this document, 1998 through 2002, recommended a slightly
|
|---|
| 2492 | different formula:
|
|---|
| 2493 |
|
|---|
| 2494 | Y = 0.212671 * R + 0.715160 * G + 0.072169 * B
|
|---|
| 2495 |
|
|---|
| 2496 | Libpng uses an integer approximation:
|
|---|
| 2497 |
|
|---|
| 2498 | Y = (6968 * R + 23434 * G + 2366 * B)/32768
|
|---|
| 2499 |
|
|---|
| 2500 | The calculation is done in a linear colorspace, if the image gamma
|
|---|
| 2501 | can be determined.
|
|---|
| 2502 |
|
|---|
| 2503 | The png_set_background() function has been described already; it tells libpng to
|
|---|
| 2504 | composite images with alpha or simple transparency against the supplied
|
|---|
| 2505 | background color. For compatibility with versions of libpng earlier than
|
|---|
| 2506 | libpng-1.5.4 it is recommended that you call the function after reading the file
|
|---|
| 2507 | header, even if you don't want to use the color in a bKGD chunk, if one exists.
|
|---|
| 2508 |
|
|---|
| 2509 | If the PNG file contains a bKGD chunk (PNG_INFO_bKGD valid),
|
|---|
| 2510 | you may use this color, or supply another color more suitable for
|
|---|
| 2511 | the current display (e.g., the background color from a web page). You
|
|---|
| 2512 | need to tell libpng how the color is represented, both the format of the
|
|---|
| 2513 | component values in the color (the number of bits) and the gamma encoding of the
|
|---|
| 2514 | color. The function takes two arguments, background_gamma_mode and need_expand
|
|---|
| 2515 | to convey this information; however, only two combinations are likely to be
|
|---|
| 2516 | useful:
|
|---|
| 2517 |
|
|---|
| 2518 | png_color_16 my_background;
|
|---|
| 2519 | png_color_16p image_background;
|
|---|
| 2520 |
|
|---|
| 2521 | if (png_get_bKGD(png_ptr, info_ptr, &image_background))
|
|---|
| 2522 | png_set_background(png_ptr, image_background,
|
|---|
| 2523 | PNG_BACKGROUND_GAMMA_FILE, 1/*needs to be expanded*/, 1);
|
|---|
| 2524 | else
|
|---|
| 2525 | png_set_background(png_ptr, &my_background,
|
|---|
| 2526 | PNG_BACKGROUND_GAMMA_SCREEN, 0/*do not expand*/, 1);
|
|---|
| 2527 |
|
|---|
| 2528 | The second call was described above - my_background is in the format of the
|
|---|
| 2529 | final, display, output produced by libpng. Because you now know the format of
|
|---|
| 2530 | the PNG it is possible to avoid the need to choose either 8-bit or 16-bit
|
|---|
| 2531 | output and to retain palette images (the palette colors will be modified
|
|---|
| 2532 | appropriately and the tRNS chunk removed.) However, if you are doing this,
|
|---|
| 2533 | take great care not to ask for transformations without checking first that
|
|---|
| 2534 | they apply!
|
|---|
| 2535 |
|
|---|
| 2536 | In the first call the background color has the original bit depth and color type
|
|---|
| 2537 | of the PNG file. So, for palette images the color is supplied as a palette
|
|---|
| 2538 | index and for low bit greyscale images the color is a reduced bit value in
|
|---|
| 2539 | image_background->gray.
|
|---|
| 2540 |
|
|---|
| 2541 | If you didn't call png_set_gamma() before reading the file header, for example
|
|---|
| 2542 | if you need your code to remain compatible with older versions of libpng prior
|
|---|
| 2543 | to libpng-1.5.4, this is the place to call it.
|
|---|
| 2544 |
|
|---|
| 2545 | Do not call it if you called png_set_alpha_mode(); doing so will damage the
|
|---|
| 2546 | settings put in place by png_set_alpha_mode(). (If png_set_alpha_mode() is
|
|---|
| 2547 | supported then you can certainly do png_set_gamma() before reading the PNG
|
|---|
| 2548 | header.)
|
|---|
| 2549 |
|
|---|
| 2550 | This API unconditionally sets the screen and file gamma values, so it will
|
|---|
| 2551 | override the value in the PNG file unless it is called before the PNG file
|
|---|
| 2552 | reading starts. For this reason you must always call it with the PNG file
|
|---|
| 2553 | value when you call it in this position:
|
|---|
| 2554 |
|
|---|
| 2555 | if (png_get_gAMA(png_ptr, info_ptr, &file_gamma))
|
|---|
| 2556 | png_set_gamma(png_ptr, screen_gamma, file_gamma);
|
|---|
| 2557 |
|
|---|
| 2558 | else
|
|---|
| 2559 | png_set_gamma(png_ptr, screen_gamma, 0.45455);
|
|---|
| 2560 |
|
|---|
| 2561 | If you need to reduce an RGB file to a paletted file, or if a paletted
|
|---|
| 2562 | file has more entries than will fit on your screen, png_set_quantize()
|
|---|
| 2563 | will do that. Note that this is a simple match quantization that merely
|
|---|
| 2564 | finds the closest color available. This should work fairly well with
|
|---|
| 2565 | optimized palettes, but fairly badly with linear color cubes. If you
|
|---|
| 2566 | pass a palette that is larger than maximum_colors, the file will
|
|---|
| 2567 | reduce the number of colors in the palette so it will fit into
|
|---|
| 2568 | maximum_colors. If there is a histogram, libpng will use it to make
|
|---|
| 2569 | more intelligent choices when reducing the palette. If there is no
|
|---|
| 2570 | histogram, it may not do as good a job.
|
|---|
| 2571 |
|
|---|
| 2572 | if (color_type & PNG_COLOR_MASK_COLOR)
|
|---|
| 2573 | {
|
|---|
| 2574 | if (png_get_valid(png_ptr, info_ptr,
|
|---|
| 2575 | PNG_INFO_PLTE))
|
|---|
| 2576 | {
|
|---|
| 2577 | png_uint_16p histogram = NULL;
|
|---|
| 2578 |
|
|---|
| 2579 | png_get_hIST(png_ptr, info_ptr,
|
|---|
| 2580 | &histogram);
|
|---|
| 2581 | png_set_quantize(png_ptr, palette, num_palette,
|
|---|
| 2582 | max_screen_colors, histogram, 1);
|
|---|
| 2583 | }
|
|---|
| 2584 |
|
|---|
| 2585 | else
|
|---|
| 2586 | {
|
|---|
| 2587 | png_color std_color_cube[MAX_SCREEN_COLORS] =
|
|---|
| 2588 | { ... colors ... };
|
|---|
| 2589 |
|
|---|
| 2590 | png_set_quantize(png_ptr, std_color_cube,
|
|---|
| 2591 | MAX_SCREEN_COLORS, MAX_SCREEN_COLORS,
|
|---|
| 2592 | NULL,0);
|
|---|
| 2593 | }
|
|---|
| 2594 | }
|
|---|
| 2595 |
|
|---|
| 2596 | PNG files describe monochrome as black being zero and white being one.
|
|---|
| 2597 | The following code will reverse this (make black be one and white be
|
|---|
| 2598 | zero):
|
|---|
| 2599 |
|
|---|
| 2600 | if (bit_depth == 1 && color_type == PNG_COLOR_TYPE_GRAY)
|
|---|
| 2601 | png_set_invert_mono(png_ptr);
|
|---|
| 2602 |
|
|---|
| 2603 | This function can also be used to invert grayscale and gray-alpha images:
|
|---|
| 2604 |
|
|---|
| 2605 | if (color_type == PNG_COLOR_TYPE_GRAY ||
|
|---|
| 2606 | color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
|
|---|
| 2607 | png_set_invert_mono(png_ptr);
|
|---|
| 2608 |
|
|---|
| 2609 | PNG files store 16-bit pixels in network byte order (big-endian,
|
|---|
| 2610 | ie. most significant bits first). This code changes the storage to the
|
|---|
| 2611 | other way (little-endian, i.e. least significant bits first, the
|
|---|
| 2612 | way PCs store them):
|
|---|
| 2613 |
|
|---|
| 2614 | if (bit_depth == 16)
|
|---|
| 2615 | png_set_swap(png_ptr);
|
|---|
| 2616 |
|
|---|
| 2617 | If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
|
|---|
| 2618 | need to change the order the pixels are packed into bytes, you can use:
|
|---|
| 2619 |
|
|---|
| 2620 | if (bit_depth < 8)
|
|---|
| 2621 | png_set_packswap(png_ptr);
|
|---|
| 2622 |
|
|---|
| 2623 | Finally, you can write your own transformation function if none of
|
|---|
| 2624 | the existing ones meets your needs. This is done by setting a callback
|
|---|
| 2625 | with
|
|---|
| 2626 |
|
|---|
| 2627 | png_set_read_user_transform_fn(png_ptr,
|
|---|
| 2628 | read_transform_fn);
|
|---|
| 2629 |
|
|---|
| 2630 | You must supply the function
|
|---|
| 2631 |
|
|---|
| 2632 | void read_transform_fn(png_structp png_ptr, png_row_infop
|
|---|
| 2633 | row_info, png_bytep data)
|
|---|
| 2634 |
|
|---|
| 2635 | See pngtest.c for a working example. Your function will be called
|
|---|
| 2636 | after all of the other transformations have been processed. Take care with
|
|---|
| 2637 | interlaced images if you do the interlace yourself - the width of the row is the
|
|---|
| 2638 | width in 'row_info', not the overall image width.
|
|---|
| 2639 |
|
|---|
| 2640 | If supported, libpng provides two information routines that you can use to find
|
|---|
| 2641 | where you are in processing the image:
|
|---|
| 2642 |
|
|---|
| 2643 | png_get_current_pass_number(png_structp png_ptr);
|
|---|
| 2644 | png_get_current_row_number(png_structp png_ptr);
|
|---|
| 2645 |
|
|---|
| 2646 | Don't try using these outside a transform callback - firstly they are only
|
|---|
| 2647 | supported if user transforms are supported, secondly they may well return
|
|---|
| 2648 | unexpected results unless the row is actually being processed at the moment they
|
|---|
| 2649 | are called.
|
|---|
| 2650 |
|
|---|
| 2651 | With interlaced
|
|---|
| 2652 | images the value returned is the row in the input sub-image image. Use
|
|---|
| 2653 | PNG_ROW_FROM_PASS_ROW(row, pass) and PNG_COL_FROM_PASS_COL(col, pass) to
|
|---|
| 2654 | find the output pixel (x,y) given an interlaced sub-image pixel (row,col,pass).
|
|---|
| 2655 |
|
|---|
| 2656 | The discussion of interlace handling above contains more information on how to
|
|---|
| 2657 | use these values.
|
|---|
| 2658 |
|
|---|
| 2659 | You can also set up a pointer to a user structure for use by your
|
|---|
| 2660 | callback function, and you can inform libpng that your transform
|
|---|
| 2661 | function will change the number of channels or bit depth with the
|
|---|
| 2662 | function
|
|---|
| 2663 |
|
|---|
| 2664 | png_set_user_transform_info(png_ptr, user_ptr,
|
|---|
| 2665 | user_depth, user_channels);
|
|---|
| 2666 |
|
|---|
| 2667 | The user's application, not libpng, is responsible for allocating and
|
|---|
| 2668 | freeing any memory required for the user structure.
|
|---|
| 2669 |
|
|---|
| 2670 | You can retrieve the pointer via the function
|
|---|
| 2671 | png_get_user_transform_ptr(). For example:
|
|---|
| 2672 |
|
|---|
| 2673 | voidp read_user_transform_ptr =
|
|---|
| 2674 | png_get_user_transform_ptr(png_ptr);
|
|---|
| 2675 |
|
|---|
| 2676 | The last thing to handle is interlacing; this is covered in detail below,
|
|---|
| 2677 | but you must call the function here if you want libpng to handle expansion
|
|---|
| 2678 | of the interlaced image.
|
|---|
| 2679 |
|
|---|
| 2680 | number_of_passes = png_set_interlace_handling(png_ptr);
|
|---|
| 2681 |
|
|---|
| 2682 | After setting the transformations, libpng can update your png_info
|
|---|
| 2683 | structure to reflect any transformations you've requested with this
|
|---|
| 2684 | call.
|
|---|
| 2685 |
|
|---|
| 2686 | png_read_update_info(png_ptr, info_ptr);
|
|---|
| 2687 |
|
|---|
| 2688 | This is most useful to update the info structure's rowbytes
|
|---|
| 2689 | field so you can use it to allocate your image memory. This function
|
|---|
| 2690 | will also update your palette with the correct screen_gamma and
|
|---|
| 2691 | background if these have been given with the calls above. You may
|
|---|
| 2692 | only call png_read_update_info() once with a particular info_ptr.
|
|---|
| 2693 |
|
|---|
| 2694 | After you call png_read_update_info(), you can allocate any
|
|---|
| 2695 | memory you need to hold the image. The row data is simply
|
|---|
| 2696 | raw byte data for all forms of images. As the actual allocation
|
|---|
| 2697 | varies among applications, no example will be given. If you
|
|---|
| 2698 | are allocating one large chunk, you will need to build an
|
|---|
| 2699 | array of pointers to each row, as it will be needed for some
|
|---|
| 2700 | of the functions below.
|
|---|
| 2701 |
|
|---|
| 2702 | Be sure that your platform can allocate the buffer that you'll need.
|
|---|
| 2703 | libpng internally checks for oversize width, but you'll need to
|
|---|
| 2704 | do your own check for number_of_rows*width*pixel_size if you are using
|
|---|
| 2705 | a multiple-row buffer:
|
|---|
| 2706 |
|
|---|
| 2707 | /* Guard against integer overflow */
|
|---|
| 2708 | if (number_of_rows > PNG_SIZE_MAX/(width*pixel_size)) {
|
|---|
| 2709 | png_error(png_ptr,"image_data buffer would be too large");
|
|---|
| 2710 | }
|
|---|
| 2711 |
|
|---|
| 2712 | Remember: Before you call png_read_update_info(), the png_get_*()
|
|---|
| 2713 | functions return the values corresponding to the original PNG image.
|
|---|
| 2714 | After you call png_read_update_info the values refer to the image
|
|---|
| 2715 | that libpng will output. Consequently you must call all the png_set_
|
|---|
| 2716 | functions before you call png_read_update_info(). This is particularly
|
|---|
| 2717 | important for png_set_interlace_handling() - if you are going to call
|
|---|
| 2718 | png_read_update_info() you must call png_set_interlace_handling() before
|
|---|
| 2719 | it unless you want to receive interlaced output.
|
|---|
| 2720 |
|
|---|
| 2721 | .SS Reading image data
|
|---|
| 2722 |
|
|---|
| 2723 | After you've allocated memory, you can read the image data.
|
|---|
| 2724 | The simplest way to do this is in one function call. If you are
|
|---|
| 2725 | allocating enough memory to hold the whole image, you can just
|
|---|
| 2726 | call png_read_image() and libpng will read in all the image data
|
|---|
| 2727 | and put it in the memory area supplied. You will need to pass in
|
|---|
| 2728 | an array of pointers to each row.
|
|---|
| 2729 |
|
|---|
| 2730 | This function automatically handles interlacing, so you don't
|
|---|
| 2731 | need to call png_set_interlace_handling() (unless you call
|
|---|
| 2732 | png_read_update_info()) or call this function multiple times, or any
|
|---|
| 2733 | of that other stuff necessary with png_read_rows().
|
|---|
| 2734 |
|
|---|
| 2735 | png_read_image(png_ptr, row_pointers);
|
|---|
| 2736 |
|
|---|
| 2737 | where row_pointers is:
|
|---|
| 2738 |
|
|---|
| 2739 | png_bytep row_pointers[height];
|
|---|
| 2740 |
|
|---|
| 2741 | You can point to void or char or whatever you use for pixels.
|
|---|
| 2742 |
|
|---|
| 2743 | If you don't want to read in the whole image at once, you can
|
|---|
| 2744 | use png_read_rows() instead. If there is no interlacing (check
|
|---|
| 2745 | interlace_type == PNG_INTERLACE_NONE), this is simple:
|
|---|
| 2746 |
|
|---|
| 2747 | png_read_rows(png_ptr, row_pointers, NULL,
|
|---|
| 2748 | number_of_rows);
|
|---|
| 2749 |
|
|---|
| 2750 | where row_pointers is the same as in the png_read_image() call.
|
|---|
| 2751 |
|
|---|
| 2752 | If you are doing this just one row at a time, you can do this with
|
|---|
| 2753 | a single row_pointer instead of an array of row_pointers:
|
|---|
| 2754 |
|
|---|
| 2755 | png_bytep row_pointer = row;
|
|---|
| 2756 | png_read_row(png_ptr, row_pointer, NULL);
|
|---|
| 2757 |
|
|---|
| 2758 | If the file is interlaced (interlace_type != 0 in the IHDR chunk), things
|
|---|
| 2759 | get somewhat harder. The only current (PNG Specification version 1.2)
|
|---|
| 2760 | interlacing type for PNG is (interlace_type == PNG_INTERLACE_ADAM7);
|
|---|
| 2761 | a somewhat complicated 2D interlace scheme, known as Adam7, that
|
|---|
| 2762 | breaks down an image into seven smaller images of varying size, based
|
|---|
| 2763 | on an 8x8 grid. This number is defined (from libpng 1.5) as
|
|---|
| 2764 | PNG_INTERLACE_ADAM7_PASSES in png.h
|
|---|
| 2765 |
|
|---|
| 2766 | libpng can fill out those images or it can give them to you "as is".
|
|---|
| 2767 | It is almost always better to have libpng handle the interlacing for you.
|
|---|
| 2768 | If you want the images filled out, there are two ways to do that. The one
|
|---|
| 2769 | mentioned in the PNG specification is to expand each pixel to cover
|
|---|
| 2770 | those pixels that have not been read yet (the "rectangle" method).
|
|---|
| 2771 | This results in a blocky image for the first pass, which gradually
|
|---|
| 2772 | smooths out as more pixels are read. The other method is the "sparkle"
|
|---|
| 2773 | method, where pixels are drawn only in their final locations, with the
|
|---|
| 2774 | rest of the image remaining whatever colors they were initialized to
|
|---|
| 2775 | before the start of the read. The first method usually looks better,
|
|---|
| 2776 | but tends to be slower, as there are more pixels to put in the rows.
|
|---|
| 2777 |
|
|---|
| 2778 | If, as is likely, you want libpng to expand the images, call this before
|
|---|
| 2779 | calling png_start_read_image() or png_read_update_info():
|
|---|
| 2780 |
|
|---|
| 2781 | if (interlace_type == PNG_INTERLACE_ADAM7)
|
|---|
| 2782 | number_of_passes
|
|---|
| 2783 | = png_set_interlace_handling(png_ptr);
|
|---|
| 2784 |
|
|---|
| 2785 | This will return the number of passes needed. Currently, this is seven,
|
|---|
| 2786 | but may change if another interlace type is added. This function can be
|
|---|
| 2787 | called even if the file is not interlaced, where it will return one pass.
|
|---|
| 2788 | You then need to read the whole image 'number_of_passes' times. Each time
|
|---|
| 2789 | will distribute the pixels from the current pass to the correct place in
|
|---|
| 2790 | the output image, so you need to supply the same rows to png_read_rows in
|
|---|
| 2791 | each pass.
|
|---|
| 2792 |
|
|---|
| 2793 | If you are not going to display the image after each pass, but are
|
|---|
| 2794 | going to wait until the entire image is read in, use the sparkle
|
|---|
| 2795 | effect. This effect is faster and the end result of either method
|
|---|
| 2796 | is exactly the same. If you are planning on displaying the image
|
|---|
| 2797 | after each pass, the "rectangle" effect is generally considered the
|
|---|
| 2798 | better looking one.
|
|---|
| 2799 |
|
|---|
| 2800 | If you only want the "sparkle" effect, just call png_read_row() or
|
|---|
| 2801 | png_read_rows() as
|
|---|
| 2802 | normal, with the third parameter NULL. Make sure you make pass over
|
|---|
| 2803 | the image number_of_passes times, and you don't change the data in the
|
|---|
| 2804 | rows between calls. You can change the locations of the data, just
|
|---|
| 2805 | not the data. Each pass only writes the pixels appropriate for that
|
|---|
| 2806 | pass, and assumes the data from previous passes is still valid.
|
|---|
| 2807 |
|
|---|
| 2808 | png_read_rows(png_ptr, row_pointers, NULL,
|
|---|
| 2809 | number_of_rows);
|
|---|
| 2810 | or
|
|---|
| 2811 | png_read_row(png_ptr, row_pointers, NULL);
|
|---|
| 2812 |
|
|---|
| 2813 | If you only want the first effect (the rectangles), do the same as
|
|---|
| 2814 | before except pass the row buffer in the third parameter, and leave
|
|---|
| 2815 | the second parameter NULL.
|
|---|
| 2816 |
|
|---|
| 2817 | png_read_rows(png_ptr, NULL, row_pointers,
|
|---|
| 2818 | number_of_rows);
|
|---|
| 2819 | or
|
|---|
| 2820 | png_read_row(png_ptr, NULL, row_pointers);
|
|---|
| 2821 |
|
|---|
| 2822 | If you don't want libpng to handle the interlacing details, just call
|
|---|
| 2823 | png_read_rows() PNG_INTERLACE_ADAM7_PASSES times to read in all the images.
|
|---|
| 2824 | Each of the images is a valid image by itself; however, you will almost
|
|---|
| 2825 | certainly need to distribute the pixels from each sub-image to the
|
|---|
| 2826 | correct place. This is where everything gets very tricky.
|
|---|
| 2827 |
|
|---|
| 2828 | If you want to retrieve the separate images you must pass the correct
|
|---|
| 2829 | number of rows to each successive call of png_read_rows(). The calculation
|
|---|
| 2830 | gets pretty complicated for small images, where some sub-images may
|
|---|
| 2831 | not even exist because either their width or height ends up zero.
|
|---|
| 2832 | libpng provides two macros to help you in 1.5 and later versions:
|
|---|
| 2833 |
|
|---|
| 2834 | png_uint_32 width = PNG_PASS_COLS(image_width, pass_number);
|
|---|
| 2835 | png_uint_32 height = PNG_PASS_ROWS(image_height, pass_number);
|
|---|
| 2836 |
|
|---|
| 2837 | Respectively these tell you the width and height of the sub-image
|
|---|
| 2838 | corresponding to the numbered pass. 'pass' is in in the range 0 to 6 -
|
|---|
| 2839 | this can be confusing because the specification refers to the same passes
|
|---|
| 2840 | as 1 to 7! Be careful, you must check both the width and height before
|
|---|
| 2841 | calling png_read_rows() and not call it for that pass if either is zero.
|
|---|
| 2842 |
|
|---|
| 2843 | You can, of course, read each sub-image row by row. If you want to
|
|---|
| 2844 | produce optimal code to make a pixel-by-pixel transformation of an
|
|---|
| 2845 | interlaced image this is the best approach; read each row of each pass,
|
|---|
| 2846 | transform it, and write it out to a new interlaced image.
|
|---|
| 2847 |
|
|---|
| 2848 | If you want to de-interlace the image yourself libpng provides further
|
|---|
| 2849 | macros to help that tell you where to place the pixels in the output image.
|
|---|
| 2850 | Because the interlacing scheme is rectangular - sub-image pixels are always
|
|---|
| 2851 | arranged on a rectangular grid - all you need to know for each pass is the
|
|---|
| 2852 | starting column and row in the output image of the first pixel plus the
|
|---|
| 2853 | spacing between each pixel. As of libpng 1.5 there are four macros to
|
|---|
| 2854 | retrieve this information:
|
|---|
| 2855 |
|
|---|
| 2856 | png_uint_32 x = PNG_PASS_START_COL(pass);
|
|---|
| 2857 | png_uint_32 y = PNG_PASS_START_ROW(pass);
|
|---|
| 2858 | png_uint_32 xStep = 1U << PNG_PASS_COL_SHIFT(pass);
|
|---|
| 2859 | png_uint_32 yStep = 1U << PNG_PASS_ROW_SHIFT(pass);
|
|---|
| 2860 |
|
|---|
| 2861 | These allow you to write the obvious loop:
|
|---|
| 2862 |
|
|---|
| 2863 | png_uint_32 input_y = 0;
|
|---|
| 2864 | png_uint_32 output_y = PNG_PASS_START_ROW(pass);
|
|---|
| 2865 |
|
|---|
| 2866 | while (output_y < output_image_height)
|
|---|
| 2867 | {
|
|---|
| 2868 | png_uint_32 input_x = 0;
|
|---|
| 2869 | png_uint_32 output_x = PNG_PASS_START_COL(pass);
|
|---|
| 2870 |
|
|---|
| 2871 | while (output_x < output_image_width)
|
|---|
| 2872 | {
|
|---|
| 2873 | image[output_y][output_x] =
|
|---|
| 2874 | subimage[pass][input_y][input_x++];
|
|---|
| 2875 |
|
|---|
| 2876 | output_x += xStep;
|
|---|
| 2877 | }
|
|---|
| 2878 |
|
|---|
| 2879 | ++input_y;
|
|---|
| 2880 | output_y += yStep;
|
|---|
| 2881 | }
|
|---|
| 2882 |
|
|---|
| 2883 | Notice that the steps between successive output rows and columns are
|
|---|
| 2884 | returned as shifts. This is possible because the pixels in the subimages
|
|---|
| 2885 | are always a power of 2 apart - 1, 2, 4 or 8 pixels - in the original
|
|---|
| 2886 | image. In practice you may need to directly calculate the output coordinate
|
|---|
| 2887 | given an input coordinate. libpng provides two further macros for this
|
|---|
| 2888 | purpose:
|
|---|
| 2889 |
|
|---|
| 2890 | png_uint_32 output_x = PNG_COL_FROM_PASS_COL(input_x, pass);
|
|---|
| 2891 | png_uint_32 output_y = PNG_ROW_FROM_PASS_ROW(input_y, pass);
|
|---|
| 2892 |
|
|---|
| 2893 | Finally a pair of macros are provided to tell you if a particular image
|
|---|
| 2894 | row or column appears in a given pass:
|
|---|
| 2895 |
|
|---|
| 2896 | int col_in_pass = PNG_COL_IN_INTERLACE_PASS(output_x, pass);
|
|---|
| 2897 | int row_in_pass = PNG_ROW_IN_INTERLACE_PASS(output_y, pass);
|
|---|
| 2898 |
|
|---|
| 2899 | Bear in mind that you will probably also need to check the width and height
|
|---|
| 2900 | of the pass in addition to the above to be sure the pass even exists!
|
|---|
| 2901 |
|
|---|
| 2902 | With any luck you are convinced by now that you don't want to do your own
|
|---|
| 2903 | interlace handling. In reality normally the only good reason for doing this
|
|---|
| 2904 | is if you are processing PNG files on a pixel-by-pixel basis and don't want
|
|---|
| 2905 | to load the whole file into memory when it is interlaced.
|
|---|
| 2906 |
|
|---|
| 2907 | libpng includes a test program, pngvalid, that illustrates reading and
|
|---|
| 2908 | writing of interlaced images. If you can't get interlacing to work in your
|
|---|
| 2909 | code and don't want to leave it to libpng (the recommended approach), see
|
|---|
| 2910 | how pngvalid.c does it.
|
|---|
| 2911 |
|
|---|
| 2912 | .SS Finishing a sequential read
|
|---|
| 2913 |
|
|---|
| 2914 | After you are finished reading the image through the
|
|---|
| 2915 | low-level interface, you can finish reading the file.
|
|---|
| 2916 |
|
|---|
| 2917 | If you want to use a different crc action for handling CRC errors in
|
|---|
| 2918 | chunks after the image data, you can call png_set_crc_action()
|
|---|
| 2919 | again at this point.
|
|---|
| 2920 |
|
|---|
| 2921 | If you are interested in comments or time, which may be stored either
|
|---|
| 2922 | before or after the image data, you should pass the separate png_info
|
|---|
| 2923 | struct if you want to keep the comments from before and after the image
|
|---|
| 2924 | separate.
|
|---|
| 2925 |
|
|---|
| 2926 | png_infop end_info = png_create_info_struct(png_ptr);
|
|---|
| 2927 |
|
|---|
| 2928 | if (!end_info)
|
|---|
| 2929 | {
|
|---|
| 2930 | png_destroy_read_struct(&png_ptr, &info_ptr,
|
|---|
| 2931 | (png_infopp)NULL);
|
|---|
| 2932 | return ERROR;
|
|---|
| 2933 | }
|
|---|
| 2934 |
|
|---|
| 2935 | png_read_end(png_ptr, end_info);
|
|---|
| 2936 |
|
|---|
| 2937 | If you are not interested, you should still call png_read_end()
|
|---|
| 2938 | but you can pass NULL, avoiding the need to create an end_info structure.
|
|---|
| 2939 | If you do this, libpng will not process any chunks after IDAT other than
|
|---|
| 2940 | skipping over them and perhaps (depending on whether you have called
|
|---|
| 2941 | png_set_crc_action) checking their CRCs while looking for the IEND chunk.
|
|---|
| 2942 |
|
|---|
| 2943 | png_read_end(png_ptr, (png_infop)NULL);
|
|---|
| 2944 |
|
|---|
| 2945 | If you don't call png_read_end(), then your file pointer will be
|
|---|
| 2946 | left pointing to the first chunk after the last IDAT, which is probably
|
|---|
| 2947 | not what you want if you expect to read something beyond the end of
|
|---|
| 2948 | the PNG datastream.
|
|---|
| 2949 |
|
|---|
| 2950 | When you are done, you can free all memory allocated by libpng like this:
|
|---|
| 2951 |
|
|---|
| 2952 | png_destroy_read_struct(&png_ptr, &info_ptr,
|
|---|
| 2953 | &end_info);
|
|---|
| 2954 |
|
|---|
| 2955 | or, if you didn't create an end_info structure,
|
|---|
| 2956 |
|
|---|
| 2957 | png_destroy_read_struct(&png_ptr, &info_ptr,
|
|---|
| 2958 | (png_infopp)NULL);
|
|---|
| 2959 |
|
|---|
| 2960 | It is also possible to individually free the info_ptr members that
|
|---|
| 2961 | point to libpng-allocated storage with the following function:
|
|---|
| 2962 |
|
|---|
| 2963 | png_free_data(png_ptr, info_ptr, mask, seq)
|
|---|
| 2964 |
|
|---|
| 2965 | mask - identifies data to be freed, a mask
|
|---|
| 2966 | containing the bitwise OR of one or
|
|---|
| 2967 | more of
|
|---|
| 2968 | PNG_FREE_PLTE, PNG_FREE_TRNS,
|
|---|
| 2969 | PNG_FREE_HIST, PNG_FREE_ICCP,
|
|---|
| 2970 | PNG_FREE_PCAL, PNG_FREE_ROWS,
|
|---|
| 2971 | PNG_FREE_SCAL, PNG_FREE_SPLT,
|
|---|
| 2972 | PNG_FREE_TEXT, PNG_FREE_UNKN,
|
|---|
| 2973 | or simply PNG_FREE_ALL
|
|---|
| 2974 |
|
|---|
| 2975 | seq - sequence number of item to be freed
|
|---|
| 2976 | (\-1 for all items)
|
|---|
| 2977 |
|
|---|
| 2978 | This function may be safely called when the relevant storage has
|
|---|
| 2979 | already been freed, or has not yet been allocated, or was allocated
|
|---|
| 2980 | by the user and not by libpng, and will in those cases do nothing.
|
|---|
| 2981 | The "seq" parameter is ignored if only one item of the selected data
|
|---|
| 2982 | type, such as PLTE, is allowed. If "seq" is not \-1, and multiple items
|
|---|
| 2983 | are allowed for the data type identified in the mask, such as text or
|
|---|
| 2984 | sPLT, only the n'th item in the structure is freed, where n is "seq".
|
|---|
| 2985 |
|
|---|
| 2986 | The default behavior is only to free data that was allocated internally
|
|---|
| 2987 | by libpng. This can be changed, so that libpng will not free the data,
|
|---|
| 2988 | or so that it will free data that was allocated by the user with png_malloc()
|
|---|
| 2989 | or png_calloc() and passed in via a png_set_*() function, with
|
|---|
| 2990 |
|
|---|
| 2991 | png_data_freer(png_ptr, info_ptr, freer, mask)
|
|---|
| 2992 |
|
|---|
| 2993 | freer - one of
|
|---|
| 2994 | PNG_DESTROY_WILL_FREE_DATA
|
|---|
| 2995 | PNG_SET_WILL_FREE_DATA
|
|---|
| 2996 | PNG_USER_WILL_FREE_DATA
|
|---|
| 2997 |
|
|---|
| 2998 | mask - which data elements are affected
|
|---|
| 2999 | same choices as in png_free_data()
|
|---|
| 3000 |
|
|---|
| 3001 | This function only affects data that has already been allocated.
|
|---|
| 3002 | You can call this function after reading the PNG data but before calling
|
|---|
| 3003 | any png_set_*() functions, to control whether the user or the png_set_*()
|
|---|
| 3004 | function is responsible for freeing any existing data that might be present,
|
|---|
| 3005 | and again after the png_set_*() functions to control whether the user
|
|---|
| 3006 | or png_destroy_*() is supposed to free the data. When the user assumes
|
|---|
| 3007 | responsibility for libpng-allocated data, the application must use
|
|---|
| 3008 | png_free() to free it, and when the user transfers responsibility to libpng
|
|---|
| 3009 | for data that the user has allocated, the user must have used png_malloc()
|
|---|
| 3010 | or png_calloc() to allocate it.
|
|---|
| 3011 |
|
|---|
| 3012 | If you allocated your row_pointers in a single block, as suggested above in
|
|---|
| 3013 | the description of the high level read interface, you must not transfer
|
|---|
| 3014 | responsibility for freeing it to the png_set_rows or png_read_destroy function,
|
|---|
| 3015 | because they would also try to free the individual row_pointers[i].
|
|---|
| 3016 |
|
|---|
| 3017 | If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
|
|---|
| 3018 | separately, do not transfer responsibility for freeing text_ptr to libpng,
|
|---|
| 3019 | because when libpng fills a png_text structure it combines these members with
|
|---|
| 3020 | the key member, and png_free_data() will free only text_ptr.key. Similarly,
|
|---|
| 3021 | if you transfer responsibility for free'ing text_ptr from libpng to your
|
|---|
| 3022 | application, your application must not separately free those members.
|
|---|
| 3023 |
|
|---|
| 3024 | The png_free_data() function will turn off the "valid" flag for anything
|
|---|
| 3025 | it frees. If you need to turn the flag off for a chunk that was freed by
|
|---|
| 3026 | your application instead of by libpng, you can use
|
|---|
| 3027 |
|
|---|
| 3028 | png_set_invalid(png_ptr, info_ptr, mask);
|
|---|
| 3029 |
|
|---|
| 3030 | mask - identifies the chunks to be made invalid,
|
|---|
| 3031 | containing the bitwise OR of one or
|
|---|
| 3032 | more of
|
|---|
| 3033 | PNG_INFO_gAMA, PNG_INFO_sBIT,
|
|---|
| 3034 | PNG_INFO_cHRM, PNG_INFO_PLTE,
|
|---|
| 3035 | PNG_INFO_tRNS, PNG_INFO_bKGD,
|
|---|
| 3036 | PNG_INFO_eXIf,
|
|---|
| 3037 | PNG_INFO_hIST, PNG_INFO_pHYs,
|
|---|
| 3038 | PNG_INFO_oFFs, PNG_INFO_tIME,
|
|---|
| 3039 | PNG_INFO_pCAL, PNG_INFO_sRGB,
|
|---|
| 3040 | PNG_INFO_iCCP, PNG_INFO_sPLT,
|
|---|
| 3041 | PNG_INFO_sCAL, PNG_INFO_IDAT
|
|---|
| 3042 |
|
|---|
| 3043 | For a more compact example of reading a PNG image, see the file example.c.
|
|---|
| 3044 |
|
|---|
| 3045 | .SS Reading PNG files progressively
|
|---|
| 3046 |
|
|---|
| 3047 | The progressive reader is slightly different from the non-progressive
|
|---|
| 3048 | reader. Instead of calling png_read_info(), png_read_rows(), and
|
|---|
| 3049 | png_read_end(), you make one call to png_process_data(), which calls
|
|---|
| 3050 | callbacks when it has the info, a row, or the end of the image. You
|
|---|
| 3051 | set up these callbacks with png_set_progressive_read_fn(). You don't
|
|---|
| 3052 | have to worry about the input/output functions of libpng, as you are
|
|---|
| 3053 | giving the library the data directly in png_process_data(). I will
|
|---|
| 3054 | assume that you have read the section on reading PNG files above,
|
|---|
| 3055 | so I will only highlight the differences (although I will show
|
|---|
| 3056 | all of the code).
|
|---|
| 3057 |
|
|---|
| 3058 | png_structp png_ptr;
|
|---|
| 3059 | png_infop info_ptr;
|
|---|
| 3060 |
|
|---|
| 3061 | /* An example code fragment of how you would
|
|---|
| 3062 | initialize the progressive reader in your
|
|---|
| 3063 | application. */
|
|---|
| 3064 | int
|
|---|
| 3065 | initialize_png_reader()
|
|---|
| 3066 | {
|
|---|
| 3067 | png_ptr = png_create_read_struct
|
|---|
| 3068 | (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
|
|---|
| 3069 | user_error_fn, user_warning_fn);
|
|---|
| 3070 |
|
|---|
| 3071 | if (!png_ptr)
|
|---|
| 3072 | return ERROR;
|
|---|
| 3073 |
|
|---|
| 3074 | info_ptr = png_create_info_struct(png_ptr);
|
|---|
| 3075 |
|
|---|
| 3076 | if (!info_ptr)
|
|---|
| 3077 | {
|
|---|
| 3078 | png_destroy_read_struct(&png_ptr,
|
|---|
| 3079 | (png_infopp)NULL, (png_infopp)NULL);
|
|---|
| 3080 | return ERROR;
|
|---|
| 3081 | }
|
|---|
| 3082 |
|
|---|
| 3083 | if (setjmp(png_jmpbuf(png_ptr)))
|
|---|
| 3084 | {
|
|---|
| 3085 | png_destroy_read_struct(&png_ptr, &info_ptr,
|
|---|
| 3086 | (png_infopp)NULL);
|
|---|
| 3087 | return ERROR;
|
|---|
| 3088 | }
|
|---|
| 3089 |
|
|---|
| 3090 | /* This one's new. You can provide functions
|
|---|
| 3091 | to be called when the header info is valid,
|
|---|
| 3092 | when each row is completed, and when the image
|
|---|
| 3093 | is finished. If you aren't using all functions,
|
|---|
| 3094 | you can specify NULL parameters. Even when all
|
|---|
| 3095 | three functions are NULL, you need to call
|
|---|
| 3096 | png_set_progressive_read_fn(). You can use
|
|---|
| 3097 | any struct as the user_ptr (cast to a void pointer
|
|---|
| 3098 | for the function call), and retrieve the pointer
|
|---|
| 3099 | from inside the callbacks using the function
|
|---|
| 3100 |
|
|---|
| 3101 | png_get_progressive_ptr(png_ptr);
|
|---|
| 3102 |
|
|---|
| 3103 | which will return a void pointer, which you have
|
|---|
| 3104 | to cast appropriately.
|
|---|
| 3105 | */
|
|---|
| 3106 | png_set_progressive_read_fn(png_ptr, (void *)user_ptr,
|
|---|
| 3107 | info_callback, row_callback, end_callback);
|
|---|
| 3108 |
|
|---|
| 3109 | return 0;
|
|---|
| 3110 | }
|
|---|
| 3111 |
|
|---|
| 3112 | /* A code fragment that you call as you receive blocks
|
|---|
| 3113 | of data */
|
|---|
| 3114 | int
|
|---|
| 3115 | process_data(png_bytep buffer, png_uint_32 length)
|
|---|
| 3116 | {
|
|---|
| 3117 | if (setjmp(png_jmpbuf(png_ptr)))
|
|---|
| 3118 | {
|
|---|
| 3119 | png_destroy_read_struct(&png_ptr, &info_ptr,
|
|---|
| 3120 | (png_infopp)NULL);
|
|---|
| 3121 | return ERROR;
|
|---|
| 3122 | }
|
|---|
| 3123 |
|
|---|
| 3124 | /* This one's new also. Simply give it a chunk
|
|---|
| 3125 | of data from the file stream (in order, of
|
|---|
| 3126 | course). On machines with segmented memory
|
|---|
| 3127 | models machines, don't give it any more than
|
|---|
| 3128 | 64K. The library seems to run fine with sizes
|
|---|
| 3129 | of 4K. Although you can give it much less if
|
|---|
| 3130 | necessary (I assume you can give it chunks of
|
|---|
| 3131 | 1 byte, I haven't tried less than 256 bytes
|
|---|
| 3132 | yet). When this function returns, you may
|
|---|
| 3133 | want to display any rows that were generated
|
|---|
| 3134 | in the row callback if you don't already do
|
|---|
| 3135 | so there.
|
|---|
| 3136 | */
|
|---|
| 3137 | png_process_data(png_ptr, info_ptr, buffer, length);
|
|---|
| 3138 |
|
|---|
| 3139 | /* At this point you can call png_process_data_skip if
|
|---|
| 3140 | you want to handle data the library will skip yourself;
|
|---|
| 3141 | it simply returns the number of bytes to skip (and stops
|
|---|
| 3142 | libpng skipping that number of bytes on the next
|
|---|
| 3143 | png_process_data call).
|
|---|
| 3144 | return 0;
|
|---|
| 3145 | }
|
|---|
| 3146 |
|
|---|
| 3147 | /* This function is called (as set by
|
|---|
| 3148 | png_set_progressive_read_fn() above) when enough data
|
|---|
| 3149 | has been supplied so all of the header has been
|
|---|
| 3150 | read.
|
|---|
| 3151 | */
|
|---|
| 3152 | void
|
|---|
| 3153 | info_callback(png_structp png_ptr, png_infop info)
|
|---|
| 3154 | {
|
|---|
| 3155 | /* Do any setup here, including setting any of
|
|---|
| 3156 | the transformations mentioned in the Reading
|
|---|
| 3157 | PNG files section. For now, you _must_ call
|
|---|
| 3158 | either png_start_read_image() or
|
|---|
| 3159 | png_read_update_info() after all the
|
|---|
| 3160 | transformations are set (even if you don't set
|
|---|
| 3161 | any). You may start getting rows before
|
|---|
| 3162 | png_process_data() returns, so this is your
|
|---|
| 3163 | last chance to prepare for that.
|
|---|
| 3164 |
|
|---|
| 3165 | This is where you turn on interlace handling,
|
|---|
| 3166 | assuming you don't want to do it yourself.
|
|---|
| 3167 |
|
|---|
| 3168 | If you need to you can stop the processing of
|
|---|
| 3169 | your original input data at this point by calling
|
|---|
| 3170 | png_process_data_pause. This returns the number
|
|---|
| 3171 | of unprocessed bytes from the last png_process_data
|
|---|
| 3172 | call - it is up to you to ensure that the next call
|
|---|
| 3173 | sees these bytes again. If you don't want to bother
|
|---|
| 3174 | with this you can get libpng to cache the unread
|
|---|
| 3175 | bytes by setting the 'save' parameter (see png.h) but
|
|---|
| 3176 | then libpng will have to copy the data internally.
|
|---|
| 3177 | */
|
|---|
| 3178 | }
|
|---|
| 3179 |
|
|---|
| 3180 | /* This function is called when each row of image
|
|---|
| 3181 | data is complete */
|
|---|
| 3182 | void
|
|---|
| 3183 | row_callback(png_structp png_ptr, png_bytep new_row,
|
|---|
| 3184 | png_uint_32 row_num, int pass)
|
|---|
| 3185 | {
|
|---|
| 3186 | /* If the image is interlaced, and you turned
|
|---|
| 3187 | on the interlace handler, this function will
|
|---|
| 3188 | be called for every row in every pass. Some
|
|---|
| 3189 | of these rows will not be changed from the
|
|---|
| 3190 | previous pass. When the row is not changed,
|
|---|
| 3191 | the new_row variable will be NULL. The rows
|
|---|
| 3192 | and passes are called in order, so you don't
|
|---|
| 3193 | really need the row_num and pass, but I'm
|
|---|
| 3194 | supplying them because it may make your life
|
|---|
| 3195 | easier.
|
|---|
| 3196 |
|
|---|
| 3197 | If you did not turn on interlace handling then
|
|---|
| 3198 | the callback is called for each row of each
|
|---|
| 3199 | sub-image when the image is interlaced. In this
|
|---|
| 3200 | case 'row_num' is the row in the sub-image, not
|
|---|
| 3201 | the row in the output image as it is in all other
|
|---|
| 3202 | cases.
|
|---|
| 3203 |
|
|---|
| 3204 | For the non-NULL rows of interlaced images when
|
|---|
| 3205 | you have switched on libpng interlace handling,
|
|---|
| 3206 | you must call png_progressive_combine_row()
|
|---|
| 3207 | passing in the row and the old row. You can
|
|---|
| 3208 | call this function for NULL rows (it will just
|
|---|
| 3209 | return) and for non-interlaced images (it just
|
|---|
| 3210 | does the memcpy for you) if it will make the
|
|---|
| 3211 | code easier. Thus, you can just do this for
|
|---|
| 3212 | all cases if you switch on interlace handling;
|
|---|
| 3213 | */
|
|---|
| 3214 |
|
|---|
| 3215 | png_progressive_combine_row(png_ptr, old_row,
|
|---|
| 3216 | new_row);
|
|---|
| 3217 |
|
|---|
| 3218 | /* where old_row is what was displayed
|
|---|
| 3219 | previously for the row. Note that the first
|
|---|
| 3220 | pass (pass == 0, really) will completely cover
|
|---|
| 3221 | the old row, so the rows do not have to be
|
|---|
| 3222 | initialized. After the first pass (and only
|
|---|
| 3223 | for interlaced images), you will have to pass
|
|---|
| 3224 | the current row, and the function will combine
|
|---|
| 3225 | the old row and the new row.
|
|---|
| 3226 |
|
|---|
| 3227 | You can also call png_process_data_pause in this
|
|---|
| 3228 | callback - see above.
|
|---|
| 3229 | */
|
|---|
| 3230 | }
|
|---|
| 3231 |
|
|---|
| 3232 | void
|
|---|
| 3233 | end_callback(png_structp png_ptr, png_infop info)
|
|---|
| 3234 | {
|
|---|
| 3235 | /* This function is called after the whole image
|
|---|
| 3236 | has been read, including any chunks after the
|
|---|
| 3237 | image (up to and including the IEND). You
|
|---|
| 3238 | will usually have the same info chunk as you
|
|---|
| 3239 | had in the header, although some data may have
|
|---|
| 3240 | been added to the comments and time fields.
|
|---|
| 3241 |
|
|---|
| 3242 | Most people won't do much here, perhaps setting
|
|---|
| 3243 | a flag that marks the image as finished.
|
|---|
| 3244 | */
|
|---|
| 3245 | }
|
|---|
| 3246 |
|
|---|
| 3247 |
|
|---|
| 3248 |
|
|---|
| 3249 | .SH IV. Writing
|
|---|
| 3250 |
|
|---|
| 3251 | Much of this is very similar to reading. However, everything of
|
|---|
| 3252 | importance is repeated here, so you won't have to constantly look
|
|---|
| 3253 | back up in the reading section to understand writing.
|
|---|
| 3254 |
|
|---|
| 3255 | .SS Setup
|
|---|
| 3256 |
|
|---|
| 3257 | You will want to do the I/O initialization before you get into libpng,
|
|---|
| 3258 | so if it doesn't work, you don't have anything to undo. If you are not
|
|---|
| 3259 | using the standard I/O functions, you will need to replace them with
|
|---|
| 3260 | custom writing functions. See the discussion under Customizing libpng.
|
|---|
| 3261 |
|
|---|
| 3262 | FILE *fp = fopen(file_name, "wb");
|
|---|
| 3263 |
|
|---|
| 3264 | if (!fp)
|
|---|
| 3265 | return ERROR;
|
|---|
| 3266 |
|
|---|
| 3267 | Next, png_struct and png_info need to be allocated and initialized.
|
|---|
| 3268 | As these can be both relatively large, you may not want to store these
|
|---|
| 3269 | on the stack, unless you have stack space to spare. Of course, you
|
|---|
| 3270 | will want to check if they return NULL. If you are also reading,
|
|---|
| 3271 | you won't want to name your read structure and your write structure
|
|---|
| 3272 | both "png_ptr"; you can call them anything you like, such as
|
|---|
| 3273 | "read_ptr" and "write_ptr". Look at pngtest.c, for example.
|
|---|
| 3274 |
|
|---|
| 3275 | png_structp png_ptr = png_create_write_struct
|
|---|
| 3276 | (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
|
|---|
| 3277 | user_error_fn, user_warning_fn);
|
|---|
| 3278 |
|
|---|
| 3279 | if (!png_ptr)
|
|---|
| 3280 | return ERROR;
|
|---|
| 3281 |
|
|---|
| 3282 | png_infop info_ptr = png_create_info_struct(png_ptr);
|
|---|
| 3283 | if (!info_ptr)
|
|---|
| 3284 | {
|
|---|
| 3285 | png_destroy_write_struct(&png_ptr,
|
|---|
| 3286 | (png_infopp)NULL);
|
|---|
| 3287 | return ERROR;
|
|---|
| 3288 | }
|
|---|
| 3289 |
|
|---|
| 3290 | If you want to use your own memory allocation routines,
|
|---|
| 3291 | define PNG_USER_MEM_SUPPORTED and use
|
|---|
| 3292 | png_create_write_struct_2() instead of png_create_write_struct():
|
|---|
| 3293 |
|
|---|
| 3294 | png_structp png_ptr = png_create_write_struct_2
|
|---|
| 3295 | (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
|
|---|
| 3296 | user_error_fn, user_warning_fn, (png_voidp)
|
|---|
| 3297 | user_mem_ptr, user_malloc_fn, user_free_fn);
|
|---|
| 3298 |
|
|---|
| 3299 | After you have these structures, you will need to set up the
|
|---|
| 3300 | error handling. When libpng encounters an error, it expects to
|
|---|
| 3301 | longjmp() back to your routine. Therefore, you will need to call
|
|---|
| 3302 | setjmp() and pass the png_jmpbuf(png_ptr). If you
|
|---|
| 3303 | write the file from different routines, you will need to update
|
|---|
| 3304 | the png_jmpbuf(png_ptr) every time you enter a new routine that will
|
|---|
| 3305 | call a png_*() function. See your documentation of setjmp/longjmp
|
|---|
| 3306 | for your compiler for more information on setjmp/longjmp. See
|
|---|
| 3307 | the discussion on libpng error handling in the Customizing Libpng
|
|---|
| 3308 | section below for more information on the libpng error handling.
|
|---|
| 3309 |
|
|---|
| 3310 | if (setjmp(png_jmpbuf(png_ptr)))
|
|---|
| 3311 | {
|
|---|
| 3312 | png_destroy_write_struct(&png_ptr, &info_ptr);
|
|---|
| 3313 | fclose(fp);
|
|---|
| 3314 | return ERROR;
|
|---|
| 3315 | }
|
|---|
| 3316 | ...
|
|---|
| 3317 | return;
|
|---|
| 3318 |
|
|---|
| 3319 | If you would rather avoid the complexity of setjmp/longjmp issues,
|
|---|
| 3320 | you can compile libpng with PNG_NO_SETJMP, in which case
|
|---|
| 3321 | errors will result in a call to PNG_ABORT() which defaults to abort().
|
|---|
| 3322 |
|
|---|
| 3323 | You can #define PNG_ABORT() to a function that does something
|
|---|
| 3324 | more useful than abort(), as long as your function does not
|
|---|
| 3325 | return.
|
|---|
| 3326 |
|
|---|
| 3327 | Checking for invalid palette index on write was added at libpng
|
|---|
| 3328 | 1.5.10. If a pixel contains an invalid (out-of-range) index libpng issues
|
|---|
| 3329 | a benign error. This is enabled by default because this condition is an
|
|---|
| 3330 | error according to the PNG specification, Clause 11.3.2, but the error can
|
|---|
| 3331 | be ignored in each png_ptr with
|
|---|
| 3332 |
|
|---|
| 3333 | png_set_check_for_invalid_index(png_ptr, 0);
|
|---|
| 3334 |
|
|---|
| 3335 | If the error is ignored, or if png_benign_error() treats it as a warning,
|
|---|
| 3336 | any invalid pixels are written as-is by the encoder, resulting in an
|
|---|
| 3337 | invalid PNG datastream as output. In this case the application is
|
|---|
| 3338 | responsible for ensuring that the pixel indexes are in range when it writes
|
|---|
| 3339 | a PLTE chunk with fewer entries than the bit depth would allow.
|
|---|
| 3340 |
|
|---|
| 3341 | Now you need to set up the output code. The default for libpng is to
|
|---|
| 3342 | use the C function fwrite(). If you use this, you will need to pass a
|
|---|
| 3343 | valid FILE * in the function png_init_io(). Be sure that the file is
|
|---|
| 3344 | opened in binary mode. Again, if you wish to handle writing data in
|
|---|
| 3345 | another way, see the discussion on libpng I/O handling in the Customizing
|
|---|
| 3346 | Libpng section below.
|
|---|
| 3347 |
|
|---|
| 3348 | png_init_io(png_ptr, fp);
|
|---|
| 3349 |
|
|---|
| 3350 | If you are embedding your PNG into a datastream such as MNG, and don't
|
|---|
| 3351 | want libpng to write the 8-byte signature, or if you have already
|
|---|
| 3352 | written the signature in your application, use
|
|---|
| 3353 |
|
|---|
| 3354 | png_set_sig_bytes(png_ptr, 8);
|
|---|
| 3355 |
|
|---|
| 3356 | to inform libpng that it should not write a signature.
|
|---|
| 3357 |
|
|---|
| 3358 | .SS Write callbacks
|
|---|
| 3359 |
|
|---|
| 3360 | At this point, you can set up a callback function that will be
|
|---|
| 3361 | called after each row has been written, which you can use to control
|
|---|
| 3362 | a progress meter or the like. It's demonstrated in pngtest.c.
|
|---|
| 3363 | You must supply a function
|
|---|
| 3364 |
|
|---|
| 3365 | void write_row_callback(png_structp png_ptr, png_uint_32 row,
|
|---|
| 3366 | int pass);
|
|---|
| 3367 | {
|
|---|
| 3368 | /* put your code here */
|
|---|
| 3369 | }
|
|---|
| 3370 |
|
|---|
| 3371 | (You can give it another name that you like instead of "write_row_callback")
|
|---|
| 3372 |
|
|---|
| 3373 | To inform libpng about your function, use
|
|---|
| 3374 |
|
|---|
| 3375 | png_set_write_status_fn(png_ptr, write_row_callback);
|
|---|
| 3376 |
|
|---|
| 3377 | When this function is called the row has already been completely processed and
|
|---|
| 3378 | it has also been written out. The 'row' and 'pass' refer to the next row to be
|
|---|
| 3379 | handled. For the
|
|---|
| 3380 | non-interlaced case the row that was just handled is simply one less than the
|
|---|
| 3381 | passed in row number, and pass will always be 0. For the interlaced case the
|
|---|
| 3382 | same applies unless the row value is 0, in which case the row just handled was
|
|---|
| 3383 | the last one from one of the preceding passes. Because interlacing may skip a
|
|---|
| 3384 | pass you cannot be sure that the preceding pass is just 'pass\-1', if you really
|
|---|
| 3385 | need to know what the last pass is record (row,pass) from the callback and use
|
|---|
| 3386 | the last recorded value each time.
|
|---|
| 3387 |
|
|---|
| 3388 | As with the user transform you can find the output row using the
|
|---|
| 3389 | PNG_ROW_FROM_PASS_ROW macro.
|
|---|
| 3390 |
|
|---|
| 3391 | You now have the option of modifying how the compression library will
|
|---|
| 3392 | run. The following functions are mainly for testing, but may be useful
|
|---|
| 3393 | in some cases, like if you need to write PNG files extremely fast and
|
|---|
| 3394 | are willing to give up some compression, or if you want to get the
|
|---|
| 3395 | maximum possible compression at the expense of slower writing. If you
|
|---|
| 3396 | have no special needs in this area, let the library do what it wants by
|
|---|
| 3397 | not calling this function at all, as it has been tuned to deliver a good
|
|---|
| 3398 | speed/compression ratio. The second parameter to png_set_filter() is
|
|---|
| 3399 | the filter method, for which the only valid values are 0 (as of the
|
|---|
| 3400 | July 1999 PNG specification, version 1.2) or 64 (if you are writing
|
|---|
| 3401 | a PNG datastream that is to be embedded in a MNG datastream). The third
|
|---|
| 3402 | parameter is a flag that indicates which filter type(s) are to be tested
|
|---|
| 3403 | for each scanline. See the PNG specification for details on the specific
|
|---|
| 3404 | filter types.
|
|---|
| 3405 |
|
|---|
| 3406 |
|
|---|
| 3407 | /* turn on or off filtering, and/or choose
|
|---|
| 3408 | specific filters. You can use either a single
|
|---|
| 3409 | PNG_FILTER_VALUE_NAME or the bitwise OR of one
|
|---|
| 3410 | or more PNG_FILTER_NAME masks.
|
|---|
| 3411 | */
|
|---|
| 3412 | png_set_filter(png_ptr, 0,
|
|---|
| 3413 | PNG_FILTER_NONE | PNG_FILTER_VALUE_NONE |
|
|---|
| 3414 | PNG_FILTER_SUB | PNG_FILTER_VALUE_SUB |
|
|---|
| 3415 | PNG_FILTER_UP | PNG_FILTER_VALUE_UP |
|
|---|
| 3416 | PNG_FILTER_AVG | PNG_FILTER_VALUE_AVG |
|
|---|
| 3417 | PNG_FILTER_PAETH | PNG_FILTER_VALUE_PAETH|
|
|---|
| 3418 | PNG_ALL_FILTERS | PNG_FAST_FILTERS);
|
|---|
| 3419 |
|
|---|
| 3420 | If an application wants to start and stop using particular filters during
|
|---|
| 3421 | compression, it should start out with all of the filters (to ensure that
|
|---|
| 3422 | the previous row of pixels will be stored in case it's needed later),
|
|---|
| 3423 | and then add and remove them after the start of compression.
|
|---|
| 3424 |
|
|---|
| 3425 | If you are writing a PNG datastream that is to be embedded in a MNG
|
|---|
| 3426 | datastream, the second parameter can be either 0 or 64.
|
|---|
| 3427 |
|
|---|
| 3428 | The png_set_compression_*() functions interface to the zlib compression
|
|---|
| 3429 | library, and should mostly be ignored unless you really know what you are
|
|---|
| 3430 | doing. The only generally useful call is png_set_compression_level()
|
|---|
| 3431 | which changes how much time zlib spends on trying to compress the image
|
|---|
| 3432 | data. See the Compression Library (zlib.h and algorithm.txt, distributed
|
|---|
| 3433 | with zlib) for details on the compression levels.
|
|---|
| 3434 |
|
|---|
| 3435 | #include zlib.h
|
|---|
| 3436 |
|
|---|
| 3437 | /* Set the zlib compression level */
|
|---|
| 3438 | png_set_compression_level(png_ptr,
|
|---|
| 3439 | Z_BEST_COMPRESSION);
|
|---|
| 3440 |
|
|---|
| 3441 | /* Set other zlib parameters for compressing IDAT */
|
|---|
| 3442 | png_set_compression_mem_level(png_ptr, 8);
|
|---|
| 3443 | png_set_compression_strategy(png_ptr,
|
|---|
| 3444 | Z_DEFAULT_STRATEGY);
|
|---|
| 3445 | png_set_compression_window_bits(png_ptr, 15);
|
|---|
| 3446 | png_set_compression_method(png_ptr, 8);
|
|---|
| 3447 | png_set_compression_buffer_size(png_ptr, 8192)
|
|---|
| 3448 |
|
|---|
| 3449 | /* Set zlib parameters for text compression
|
|---|
| 3450 | * If you don't call these, the parameters
|
|---|
| 3451 | * fall back on those defined for IDAT chunks
|
|---|
| 3452 | */
|
|---|
| 3453 | png_set_text_compression_mem_level(png_ptr, 8);
|
|---|
| 3454 | png_set_text_compression_strategy(png_ptr,
|
|---|
| 3455 | Z_DEFAULT_STRATEGY);
|
|---|
| 3456 | png_set_text_compression_window_bits(png_ptr, 15);
|
|---|
| 3457 | png_set_text_compression_method(png_ptr, 8);
|
|---|
| 3458 |
|
|---|
| 3459 | .SS Setting the contents of info for output
|
|---|
| 3460 |
|
|---|
| 3461 | You now need to fill in the png_info structure with all the data you
|
|---|
| 3462 | wish to write before the actual image. Note that the only thing you
|
|---|
| 3463 | are allowed to write after the image is the text chunks and the time
|
|---|
| 3464 | chunk (as of PNG Specification 1.2, anyway). See png_write_end() and
|
|---|
| 3465 | the latest PNG specification for more information on that. If you
|
|---|
| 3466 | wish to write them before the image, fill them in now, and flag that
|
|---|
| 3467 | data as being valid. If you want to wait until after the data, don't
|
|---|
| 3468 | fill them until png_write_end(). For all the fields in png_info and
|
|---|
| 3469 | their data types, see png.h. For explanations of what the fields
|
|---|
| 3470 | contain, see the PNG specification.
|
|---|
| 3471 |
|
|---|
| 3472 | Some of the more important parts of the png_info are:
|
|---|
| 3473 |
|
|---|
| 3474 | png_set_IHDR(png_ptr, info_ptr, width, height,
|
|---|
| 3475 | bit_depth, color_type, interlace_type,
|
|---|
| 3476 | compression_type, filter_method)
|
|---|
| 3477 |
|
|---|
| 3478 | width - holds the width of the image
|
|---|
| 3479 | in pixels (up to 2^31).
|
|---|
| 3480 |
|
|---|
| 3481 | height - holds the height of the image
|
|---|
| 3482 | in pixels (up to 2^31).
|
|---|
| 3483 |
|
|---|
| 3484 | bit_depth - holds the bit depth of one of the
|
|---|
| 3485 | image channels.
|
|---|
| 3486 | (valid values are 1, 2, 4, 8, 16
|
|---|
| 3487 | and depend also on the
|
|---|
| 3488 | color_type. See also significant
|
|---|
| 3489 | bits (sBIT) below).
|
|---|
| 3490 |
|
|---|
| 3491 | color_type - describes which color/alpha
|
|---|
| 3492 | channels are present.
|
|---|
| 3493 | PNG_COLOR_TYPE_GRAY
|
|---|
| 3494 | (bit depths 1, 2, 4, 8, 16)
|
|---|
| 3495 | PNG_COLOR_TYPE_GRAY_ALPHA
|
|---|
| 3496 | (bit depths 8, 16)
|
|---|
| 3497 | PNG_COLOR_TYPE_PALETTE
|
|---|
| 3498 | (bit depths 1, 2, 4, 8)
|
|---|
| 3499 | PNG_COLOR_TYPE_RGB
|
|---|
| 3500 | (bit_depths 8, 16)
|
|---|
| 3501 | PNG_COLOR_TYPE_RGB_ALPHA
|
|---|
| 3502 | (bit_depths 8, 16)
|
|---|
| 3503 |
|
|---|
| 3504 | PNG_COLOR_MASK_PALETTE
|
|---|
| 3505 | PNG_COLOR_MASK_COLOR
|
|---|
| 3506 | PNG_COLOR_MASK_ALPHA
|
|---|
| 3507 |
|
|---|
| 3508 | interlace_type - PNG_INTERLACE_NONE or
|
|---|
| 3509 | PNG_INTERLACE_ADAM7
|
|---|
| 3510 |
|
|---|
| 3511 | compression_type - (must be
|
|---|
| 3512 | PNG_COMPRESSION_TYPE_DEFAULT)
|
|---|
| 3513 |
|
|---|
| 3514 | filter_method - (must be PNG_FILTER_TYPE_DEFAULT
|
|---|
| 3515 | or, if you are writing a PNG to
|
|---|
| 3516 | be embedded in a MNG datastream,
|
|---|
| 3517 | can also be
|
|---|
| 3518 | PNG_INTRAPIXEL_DIFFERENCING)
|
|---|
| 3519 |
|
|---|
| 3520 | If you call png_set_IHDR(), the call must appear before any of the
|
|---|
| 3521 | other png_set_*() functions, because they might require access to some of
|
|---|
| 3522 | the IHDR settings. The remaining png_set_*() functions can be called
|
|---|
| 3523 | in any order.
|
|---|
| 3524 |
|
|---|
| 3525 | If you wish, you can reset the compression_type, interlace_type, or
|
|---|
| 3526 | filter_method later by calling png_set_IHDR() again; if you do this, the
|
|---|
| 3527 | width, height, bit_depth, and color_type must be the same in each call.
|
|---|
| 3528 |
|
|---|
| 3529 | png_set_PLTE(png_ptr, info_ptr, palette,
|
|---|
| 3530 | num_palette);
|
|---|
| 3531 |
|
|---|
| 3532 | palette - the palette for the file
|
|---|
| 3533 | (array of png_color)
|
|---|
| 3534 | num_palette - number of entries in the palette
|
|---|
| 3535 |
|
|---|
| 3536 |
|
|---|
| 3537 | png_set_gAMA(png_ptr, info_ptr, file_gamma);
|
|---|
| 3538 | png_set_gAMA_fixed(png_ptr, info_ptr, int_file_gamma);
|
|---|
| 3539 |
|
|---|
| 3540 | file_gamma - the gamma at which the image was
|
|---|
| 3541 | created (PNG_INFO_gAMA)
|
|---|
| 3542 |
|
|---|
| 3543 | int_file_gamma - 100,000 times the gamma at which
|
|---|
| 3544 | the image was created
|
|---|
| 3545 |
|
|---|
| 3546 | png_set_cHRM(png_ptr, info_ptr, white_x, white_y, red_x, red_y,
|
|---|
| 3547 | green_x, green_y, blue_x, blue_y)
|
|---|
| 3548 | png_set_cHRM_XYZ(png_ptr, info_ptr, red_X, red_Y, red_Z, green_X,
|
|---|
| 3549 | green_Y, green_Z, blue_X, blue_Y, blue_Z)
|
|---|
| 3550 | png_set_cHRM_fixed(png_ptr, info_ptr, int_white_x, int_white_y,
|
|---|
| 3551 | int_red_x, int_red_y, int_green_x, int_green_y,
|
|---|
| 3552 | int_blue_x, int_blue_y)
|
|---|
| 3553 | png_set_cHRM_XYZ_fixed(png_ptr, info_ptr, int_red_X, int_red_Y,
|
|---|
| 3554 | int_red_Z, int_green_X, int_green_Y, int_green_Z,
|
|---|
| 3555 | int_blue_X, int_blue_Y, int_blue_Z)
|
|---|
| 3556 |
|
|---|
| 3557 | {white,red,green,blue}_{x,y}
|
|---|
| 3558 | A color space encoding specified using the chromaticities
|
|---|
| 3559 | of the end points and the white point.
|
|---|
| 3560 |
|
|---|
| 3561 | {red,green,blue}_{X,Y,Z}
|
|---|
| 3562 | A color space encoding specified using the encoding end
|
|---|
| 3563 | points - the CIE tristimulus specification of the intended
|
|---|
| 3564 | color of the red, green and blue channels in the PNG RGB
|
|---|
| 3565 | data. The white point is simply the sum of the three end
|
|---|
| 3566 | points.
|
|---|
| 3567 |
|
|---|
| 3568 | png_set_sRGB(png_ptr, info_ptr, srgb_intent);
|
|---|
| 3569 |
|
|---|
| 3570 | srgb_intent - the rendering intent
|
|---|
| 3571 | (PNG_INFO_sRGB) The presence of
|
|---|
| 3572 | the sRGB chunk means that the pixel
|
|---|
| 3573 | data is in the sRGB color space.
|
|---|
| 3574 | This chunk also implies specific
|
|---|
| 3575 | values of gAMA and cHRM. Rendering
|
|---|
| 3576 | intent is the CSS-1 property that
|
|---|
| 3577 | has been defined by the International
|
|---|
| 3578 | Color Consortium
|
|---|
| 3579 | (http://www.color.org).
|
|---|
| 3580 | It can be one of
|
|---|
| 3581 | PNG_sRGB_INTENT_SATURATION,
|
|---|
| 3582 | PNG_sRGB_INTENT_PERCEPTUAL,
|
|---|
| 3583 | PNG_sRGB_INTENT_ABSOLUTE, or
|
|---|
| 3584 | PNG_sRGB_INTENT_RELATIVE.
|
|---|
| 3585 |
|
|---|
| 3586 |
|
|---|
| 3587 | png_set_sRGB_gAMA_and_cHRM(png_ptr, info_ptr,
|
|---|
| 3588 | srgb_intent);
|
|---|
| 3589 |
|
|---|
| 3590 | srgb_intent - the rendering intent
|
|---|
| 3591 | (PNG_INFO_sRGB) The presence of the
|
|---|
| 3592 | sRGB chunk means that the pixel
|
|---|
| 3593 | data is in the sRGB color space.
|
|---|
| 3594 | This function also causes gAMA and
|
|---|
| 3595 | cHRM chunks with the specific values
|
|---|
| 3596 | that are consistent with sRGB to be
|
|---|
| 3597 | written.
|
|---|
| 3598 |
|
|---|
| 3599 | png_set_iCCP(png_ptr, info_ptr, name, compression_type,
|
|---|
| 3600 | profile, proflen);
|
|---|
| 3601 |
|
|---|
| 3602 | name - The profile name.
|
|---|
| 3603 |
|
|---|
| 3604 | compression_type - The compression type; always
|
|---|
| 3605 | PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
|
|---|
| 3606 | You may give NULL to this argument to
|
|---|
| 3607 | ignore it.
|
|---|
| 3608 |
|
|---|
| 3609 | profile - International Color Consortium color
|
|---|
| 3610 | profile data. May contain NULs.
|
|---|
| 3611 |
|
|---|
| 3612 | proflen - length of profile data in bytes.
|
|---|
| 3613 |
|
|---|
| 3614 | png_set_sBIT(png_ptr, info_ptr, sig_bit);
|
|---|
| 3615 |
|
|---|
| 3616 | sig_bit - the number of significant bits for
|
|---|
| 3617 | (PNG_INFO_sBIT) each of the gray, red,
|
|---|
| 3618 | green, and blue channels, whichever are
|
|---|
| 3619 | appropriate for the given color type
|
|---|
| 3620 | (png_color_16)
|
|---|
| 3621 |
|
|---|
| 3622 | png_set_tRNS(png_ptr, info_ptr, trans_alpha,
|
|---|
| 3623 | num_trans, trans_color);
|
|---|
| 3624 |
|
|---|
| 3625 | trans_alpha - array of alpha (transparency)
|
|---|
| 3626 | entries for palette (PNG_INFO_tRNS)
|
|---|
| 3627 |
|
|---|
| 3628 | num_trans - number of transparent entries
|
|---|
| 3629 | (PNG_INFO_tRNS)
|
|---|
| 3630 |
|
|---|
| 3631 | trans_color - graylevel or color sample values
|
|---|
| 3632 | (in order red, green, blue) of the
|
|---|
| 3633 | single transparent color for
|
|---|
| 3634 | non-paletted images (PNG_INFO_tRNS)
|
|---|
| 3635 |
|
|---|
| 3636 | png_set_eXIf_1(png_ptr, info_ptr, num_exif, exif);
|
|---|
| 3637 |
|
|---|
| 3638 | exif - Exif profile (array of
|
|---|
| 3639 | png_byte) (PNG_INFO_eXIf)
|
|---|
| 3640 |
|
|---|
| 3641 | png_set_hIST(png_ptr, info_ptr, hist);
|
|---|
| 3642 |
|
|---|
| 3643 | hist - histogram of palette (array of
|
|---|
| 3644 | png_uint_16) (PNG_INFO_hIST)
|
|---|
| 3645 |
|
|---|
| 3646 | png_set_tIME(png_ptr, info_ptr, mod_time);
|
|---|
| 3647 |
|
|---|
| 3648 | mod_time - time image was last modified
|
|---|
| 3649 | (PNG_VALID_tIME)
|
|---|
| 3650 |
|
|---|
| 3651 | png_set_bKGD(png_ptr, info_ptr, background);
|
|---|
| 3652 |
|
|---|
| 3653 | background - background color (of type
|
|---|
| 3654 | png_color_16p) (PNG_VALID_bKGD)
|
|---|
| 3655 |
|
|---|
| 3656 | png_set_text(png_ptr, info_ptr, text_ptr, num_text);
|
|---|
| 3657 |
|
|---|
| 3658 | text_ptr - array of png_text holding image
|
|---|
| 3659 | comments
|
|---|
| 3660 |
|
|---|
| 3661 | text_ptr[i].compression - type of compression used
|
|---|
| 3662 | on "text" PNG_TEXT_COMPRESSION_NONE
|
|---|
| 3663 | PNG_TEXT_COMPRESSION_zTXt
|
|---|
| 3664 | PNG_ITXT_COMPRESSION_NONE
|
|---|
| 3665 | PNG_ITXT_COMPRESSION_zTXt
|
|---|
| 3666 | text_ptr[i].key - keyword for comment. Must contain
|
|---|
| 3667 | 1-79 characters.
|
|---|
| 3668 | text_ptr[i].text - text comments for current
|
|---|
| 3669 | keyword. Can be NULL or empty.
|
|---|
| 3670 | text_ptr[i].text_length - length of text string,
|
|---|
| 3671 | after decompression, 0 for iTXt
|
|---|
| 3672 | text_ptr[i].itxt_length - length of itxt string,
|
|---|
| 3673 | after decompression, 0 for tEXt/zTXt
|
|---|
| 3674 | text_ptr[i].lang - language of comment (NULL or
|
|---|
| 3675 | empty for unknown).
|
|---|
| 3676 | text_ptr[i].translated_keyword - keyword in UTF-8 (NULL
|
|---|
| 3677 | or empty for unknown).
|
|---|
| 3678 |
|
|---|
| 3679 | Note that the itxt_length, lang, and lang_key
|
|---|
| 3680 | members of the text_ptr structure only exist when the
|
|---|
| 3681 | library is built with iTXt chunk support. Prior to
|
|---|
| 3682 | libpng-1.4.0 the library was built by default without
|
|---|
| 3683 | iTXt support. Also note that when iTXt is supported,
|
|---|
| 3684 | they contain NULL pointers when the "compression"
|
|---|
| 3685 | field contains PNG_TEXT_COMPRESSION_NONE or
|
|---|
| 3686 | PNG_TEXT_COMPRESSION_zTXt.
|
|---|
| 3687 |
|
|---|
| 3688 | num_text - number of comments
|
|---|
| 3689 |
|
|---|
| 3690 | png_set_sPLT(png_ptr, info_ptr, &palette_ptr,
|
|---|
| 3691 | num_spalettes);
|
|---|
| 3692 |
|
|---|
| 3693 | palette_ptr - array of png_sPLT_struct structures
|
|---|
| 3694 | to be added to the list of palettes
|
|---|
| 3695 | in the info structure.
|
|---|
| 3696 | num_spalettes - number of palette structures to be
|
|---|
| 3697 | added.
|
|---|
| 3698 |
|
|---|
| 3699 | png_set_oFFs(png_ptr, info_ptr, offset_x, offset_y,
|
|---|
| 3700 | unit_type);
|
|---|
| 3701 |
|
|---|
| 3702 | offset_x - positive offset from the left
|
|---|
| 3703 | edge of the screen
|
|---|
| 3704 |
|
|---|
| 3705 | offset_y - positive offset from the top
|
|---|
| 3706 | edge of the screen
|
|---|
| 3707 |
|
|---|
| 3708 | unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
|
|---|
| 3709 |
|
|---|
| 3710 | png_set_pHYs(png_ptr, info_ptr, res_x, res_y,
|
|---|
| 3711 | unit_type);
|
|---|
| 3712 |
|
|---|
| 3713 | res_x - pixels/unit physical resolution
|
|---|
| 3714 | in x direction
|
|---|
| 3715 |
|
|---|
| 3716 | res_y - pixels/unit physical resolution
|
|---|
| 3717 | in y direction
|
|---|
| 3718 |
|
|---|
| 3719 | unit_type - PNG_RESOLUTION_UNKNOWN,
|
|---|
| 3720 | PNG_RESOLUTION_METER
|
|---|
| 3721 |
|
|---|
| 3722 | png_set_sCAL(png_ptr, info_ptr, unit, width, height)
|
|---|
| 3723 |
|
|---|
| 3724 | unit - physical scale units (an integer)
|
|---|
| 3725 |
|
|---|
| 3726 | width - width of a pixel in physical scale units
|
|---|
| 3727 |
|
|---|
| 3728 | height - height of a pixel in physical scale units
|
|---|
| 3729 | (width and height are doubles)
|
|---|
| 3730 |
|
|---|
| 3731 | png_set_sCAL_s(png_ptr, info_ptr, unit, width, height)
|
|---|
| 3732 |
|
|---|
| 3733 | unit - physical scale units (an integer)
|
|---|
| 3734 |
|
|---|
| 3735 | width - width of a pixel in physical scale units
|
|---|
| 3736 | expressed as a string
|
|---|
| 3737 |
|
|---|
| 3738 | height - height of a pixel in physical scale units
|
|---|
| 3739 | (width and height are strings like "2.54")
|
|---|
| 3740 |
|
|---|
| 3741 | png_set_unknown_chunks(png_ptr, info_ptr, &unknowns,
|
|---|
| 3742 | num_unknowns)
|
|---|
| 3743 |
|
|---|
| 3744 | unknowns - array of png_unknown_chunk
|
|---|
| 3745 | structures holding unknown chunks
|
|---|
| 3746 | unknowns[i].name - name of unknown chunk
|
|---|
| 3747 | unknowns[i].data - data of unknown chunk
|
|---|
| 3748 | unknowns[i].size - size of unknown chunk's data
|
|---|
| 3749 | unknowns[i].location - position to write chunk in file
|
|---|
| 3750 | 0: do not write chunk
|
|---|
| 3751 | PNG_HAVE_IHDR: before PLTE
|
|---|
| 3752 | PNG_HAVE_PLTE: before IDAT
|
|---|
| 3753 | PNG_AFTER_IDAT: after IDAT
|
|---|
| 3754 |
|
|---|
| 3755 | The "location" member is set automatically according to
|
|---|
| 3756 | what part of the output file has already been written.
|
|---|
| 3757 | You can change its value after calling png_set_unknown_chunks()
|
|---|
| 3758 | as demonstrated in pngtest.c. Within each of the "locations",
|
|---|
| 3759 | the chunks are sequenced according to their position in the
|
|---|
| 3760 | structure (that is, the value of "i", which is the order in which
|
|---|
| 3761 | the chunk was either read from the input file or defined with
|
|---|
| 3762 | png_set_unknown_chunks).
|
|---|
| 3763 |
|
|---|
| 3764 | A quick word about text and num_text. text is an array of png_text
|
|---|
| 3765 | structures. num_text is the number of valid structures in the array.
|
|---|
| 3766 | Each png_text structure holds a language code, a keyword, a text value,
|
|---|
| 3767 | and a compression type.
|
|---|
| 3768 |
|
|---|
| 3769 | The compression types have the same valid numbers as the compression
|
|---|
| 3770 | types of the image data. Currently, the only valid number is zero.
|
|---|
| 3771 | However, you can store text either compressed or uncompressed, unlike
|
|---|
| 3772 | images, which always have to be compressed. So if you don't want the
|
|---|
| 3773 | text compressed, set the compression type to PNG_TEXT_COMPRESSION_NONE.
|
|---|
| 3774 | Because tEXt and zTXt chunks don't have a language field, if you
|
|---|
| 3775 | specify PNG_TEXT_COMPRESSION_NONE or PNG_TEXT_COMPRESSION_zTXt
|
|---|
| 3776 | any language code or translated keyword will not be written out.
|
|---|
| 3777 |
|
|---|
| 3778 | Until text gets around a few hundred bytes, it is not worth compressing it.
|
|---|
| 3779 | After the text has been written out to the file, the compression type
|
|---|
| 3780 | is set to PNG_TEXT_COMPRESSION_NONE_WR or PNG_TEXT_COMPRESSION_zTXt_WR,
|
|---|
| 3781 | so that it isn't written out again at the end (in case you are calling
|
|---|
| 3782 | png_write_end() with the same struct).
|
|---|
| 3783 |
|
|---|
| 3784 | The keywords that are given in the PNG Specification are:
|
|---|
| 3785 |
|
|---|
| 3786 | Title Short (one line) title or
|
|---|
| 3787 | caption for image
|
|---|
| 3788 |
|
|---|
| 3789 | Author Name of image's creator
|
|---|
| 3790 |
|
|---|
| 3791 | Description Description of image (possibly long)
|
|---|
| 3792 |
|
|---|
| 3793 | Copyright Copyright notice
|
|---|
| 3794 |
|
|---|
| 3795 | Creation Time Time of original image creation
|
|---|
| 3796 | (usually RFC 1123 format, see below)
|
|---|
| 3797 |
|
|---|
| 3798 | Software Software used to create the image
|
|---|
| 3799 |
|
|---|
| 3800 | Disclaimer Legal disclaimer
|
|---|
| 3801 |
|
|---|
| 3802 | Warning Warning of nature of content
|
|---|
| 3803 |
|
|---|
| 3804 | Source Device used to create the image
|
|---|
| 3805 |
|
|---|
| 3806 | Comment Miscellaneous comment; conversion
|
|---|
| 3807 | from other image format
|
|---|
| 3808 |
|
|---|
| 3809 | The keyword-text pairs work like this. Keywords should be short
|
|---|
| 3810 | simple descriptions of what the comment is about. Some typical
|
|---|
| 3811 | keywords are found in the PNG specification, as is some recommendations
|
|---|
| 3812 | on keywords. You can repeat keywords in a file. You can even write
|
|---|
| 3813 | some text before the image and some after. For example, you may want
|
|---|
| 3814 | to put a description of the image before the image, but leave the
|
|---|
| 3815 | disclaimer until after, so viewers working over modem connections
|
|---|
| 3816 | don't have to wait for the disclaimer to go over the modem before
|
|---|
| 3817 | they start seeing the image. Finally, keywords should be full
|
|---|
| 3818 | words, not abbreviations. Keywords and text are in the ISO 8859-1
|
|---|
| 3819 | (Latin-1) character set (a superset of regular ASCII) and can not
|
|---|
| 3820 | contain NUL characters, and should not contain control or other
|
|---|
| 3821 | unprintable characters. To make the comments widely readable, stick
|
|---|
| 3822 | with basic ASCII, and avoid machine specific character set extensions
|
|---|
| 3823 | like the IBM-PC character set. The keyword must be present, but
|
|---|
| 3824 | you can leave off the text string on non-compressed pairs.
|
|---|
| 3825 | Compressed pairs must have a text string, as only the text string
|
|---|
| 3826 | is compressed anyway, so the compression would be meaningless.
|
|---|
| 3827 |
|
|---|
| 3828 | PNG supports modification time via the png_time structure. Two
|
|---|
| 3829 | conversion routines are provided, png_convert_from_time_t() for
|
|---|
| 3830 | time_t and png_convert_from_struct_tm() for struct tm. The
|
|---|
| 3831 | time_t routine uses gmtime(). You don't have to use either of
|
|---|
| 3832 | these, but if you wish to fill in the png_time structure directly,
|
|---|
| 3833 | you should provide the time in universal time (GMT) if possible
|
|---|
| 3834 | instead of your local time. Note that the year number is the full
|
|---|
| 3835 | year (e.g. 1998, rather than 98 - PNG is year 2000 compliant!), and
|
|---|
| 3836 | that months start with 1.
|
|---|
| 3837 |
|
|---|
| 3838 | If you want to store the time of the original image creation, you should
|
|---|
| 3839 | use a plain tEXt chunk with the "Creation Time" keyword. This is
|
|---|
| 3840 | necessary because the "creation time" of a PNG image is somewhat vague,
|
|---|
| 3841 | depending on whether you mean the PNG file, the time the image was
|
|---|
| 3842 | created in a non-PNG format, a still photo from which the image was
|
|---|
| 3843 | scanned, or possibly the subject matter itself. In order to facilitate
|
|---|
| 3844 | machine-readable dates, it is recommended that the "Creation Time"
|
|---|
| 3845 | tEXt chunk use RFC 1123 format dates (e.g. "22 May 1997 18:07:10 GMT"),
|
|---|
| 3846 | although this isn't a requirement. Unlike the tIME chunk, the
|
|---|
| 3847 | "Creation Time" tEXt chunk is not expected to be automatically changed
|
|---|
| 3848 | by the software. To facilitate the use of RFC 1123 dates, a function
|
|---|
| 3849 | png_convert_to_rfc1123_buffer(buffer, png_timep) is provided to
|
|---|
| 3850 | convert from PNG time to an RFC 1123 format string. The caller must provide
|
|---|
| 3851 | a writeable buffer of at least 29 bytes.
|
|---|
| 3852 |
|
|---|
| 3853 | .SS Writing unknown chunks
|
|---|
| 3854 |
|
|---|
| 3855 | You can use the png_set_unknown_chunks function to queue up private chunks
|
|---|
| 3856 | for writing. You give it a chunk name, location, raw data, and a size. You
|
|---|
| 3857 | also must use png_set_keep_unknown_chunks() to ensure that libpng will
|
|---|
| 3858 | handle them. That's all there is to it. The chunks will be written by the
|
|---|
| 3859 | next following png_write_info_before_PLTE, png_write_info, or png_write_end
|
|---|
| 3860 | function, depending upon the specified location. Any chunks previously
|
|---|
| 3861 | read into the info structure's unknown-chunk list will also be written out
|
|---|
| 3862 | in a sequence that satisfies the PNG specification's ordering rules.
|
|---|
| 3863 |
|
|---|
| 3864 | Here is an example of writing two private chunks, prVt and miNE:
|
|---|
| 3865 |
|
|---|
| 3866 | #ifdef PNG_WRITE_UNKNOWN_CHUNKS_SUPPORTED
|
|---|
| 3867 | /* Set unknown chunk data */
|
|---|
| 3868 | png_unknown_chunk unk_chunk[2];
|
|---|
| 3869 | strcpy((char *) unk_chunk[0].name, "prVt";
|
|---|
| 3870 | unk_chunk[0].data = (unsigned char *) "PRIVATE DATA";
|
|---|
| 3871 | unk_chunk[0].size = strlen(unk_chunk[0].data)+1;
|
|---|
| 3872 | unk_chunk[0].location = PNG_HAVE_IHDR;
|
|---|
| 3873 | strcpy((char *) unk_chunk[1].name, "miNE";
|
|---|
| 3874 | unk_chunk[1].data = (unsigned char *) "MY CHUNK DATA";
|
|---|
| 3875 | unk_chunk[1].size = strlen(unk_chunk[0].data)+1;
|
|---|
| 3876 | unk_chunk[1].location = PNG_AFTER_IDAT;
|
|---|
| 3877 | png_set_unknown_chunks(write_ptr, write_info_ptr,
|
|---|
| 3878 | unk_chunk, 2);
|
|---|
| 3879 | /* Needed because miNE is not safe-to-copy */
|
|---|
| 3880 | png_set_keep_unknown_chunks(png, PNG_HANDLE_CHUNK_ALWAYS,
|
|---|
| 3881 | (png_bytep) "miNE", 1);
|
|---|
| 3882 | # if PNG_LIBPNG_VER < 10600
|
|---|
| 3883 | /* Deal with unknown chunk location bug in 1.5.x and earlier */
|
|---|
| 3884 | png_set_unknown_chunk_location(png, info, 0, PNG_HAVE_IHDR);
|
|---|
| 3885 | png_set_unknown_chunk_location(png, info, 1, PNG_AFTER_IDAT);
|
|---|
| 3886 | # endif
|
|---|
| 3887 | # if PNG_LIBPNG_VER < 10500
|
|---|
| 3888 | /* PNG_AFTER_IDAT writes two copies of the chunk prior to libpng-1.5.0,
|
|---|
| 3889 | * one before IDAT and another after IDAT, so don't use it; only use
|
|---|
| 3890 | * PNG_HAVE_IHDR location. This call resets the location previously
|
|---|
| 3891 | * set by assignment and png_set_unknown_chunk_location() for chunk 1.
|
|---|
| 3892 | */
|
|---|
| 3893 | png_set_unknown_chunk_location(png, info, 1, PNG_HAVE_IHDR);
|
|---|
| 3894 | # endif
|
|---|
| 3895 | #endif
|
|---|
| 3896 |
|
|---|
| 3897 | .SS The high-level write interface
|
|---|
| 3898 |
|
|---|
| 3899 | At this point there are two ways to proceed; through the high-level
|
|---|
| 3900 | write interface, or through a sequence of low-level write operations.
|
|---|
| 3901 | You can use the high-level interface if your image data is present
|
|---|
| 3902 | in the info structure. All defined output
|
|---|
| 3903 | transformations are permitted, enabled by the following masks.
|
|---|
| 3904 |
|
|---|
| 3905 | PNG_TRANSFORM_IDENTITY No transformation
|
|---|
| 3906 | PNG_TRANSFORM_PACKING Pack 1, 2 and 4-bit samples
|
|---|
| 3907 | PNG_TRANSFORM_PACKSWAP Change order of packed
|
|---|
| 3908 | pixels to LSB first
|
|---|
| 3909 | PNG_TRANSFORM_INVERT_MONO Invert monochrome images
|
|---|
| 3910 | PNG_TRANSFORM_SHIFT Normalize pixels to the
|
|---|
| 3911 | sBIT depth
|
|---|
| 3912 | PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
|
|---|
| 3913 | to BGRA
|
|---|
| 3914 | PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
|
|---|
| 3915 | to AG
|
|---|
| 3916 | PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
|
|---|
| 3917 | to transparency
|
|---|
| 3918 | PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
|
|---|
| 3919 | PNG_TRANSFORM_STRIP_FILLER Strip out filler
|
|---|
| 3920 | bytes (deprecated).
|
|---|
| 3921 | PNG_TRANSFORM_STRIP_FILLER_BEFORE Strip out leading
|
|---|
| 3922 | filler bytes
|
|---|
| 3923 | PNG_TRANSFORM_STRIP_FILLER_AFTER Strip out trailing
|
|---|
| 3924 | filler bytes
|
|---|
| 3925 |
|
|---|
| 3926 | If you have valid image data in the info structure (you can use
|
|---|
| 3927 | png_set_rows() to put image data in the info structure), simply do this:
|
|---|
| 3928 |
|
|---|
| 3929 | png_write_png(png_ptr, info_ptr, png_transforms, NULL)
|
|---|
| 3930 |
|
|---|
| 3931 | where png_transforms is an integer containing the bitwise OR of some set of
|
|---|
| 3932 | transformation flags. This call is equivalent to png_write_info(),
|
|---|
| 3933 | followed the set of transformations indicated by the transform mask,
|
|---|
| 3934 | then png_write_image(), and finally png_write_end().
|
|---|
| 3935 |
|
|---|
| 3936 | (The final parameter of this call is not yet used. Someday it might point
|
|---|
| 3937 | to transformation parameters required by some future output transform.)
|
|---|
| 3938 |
|
|---|
| 3939 | You must use png_transforms and not call any png_set_transform() functions
|
|---|
| 3940 | when you use png_write_png().
|
|---|
| 3941 |
|
|---|
| 3942 | .SS The low-level write interface
|
|---|
| 3943 |
|
|---|
| 3944 | If you are going the low-level route instead, you are now ready to
|
|---|
| 3945 | write all the file information up to the actual image data. You do
|
|---|
| 3946 | this with a call to png_write_info().
|
|---|
| 3947 |
|
|---|
| 3948 | png_write_info(png_ptr, info_ptr);
|
|---|
| 3949 |
|
|---|
| 3950 | Note that there is one transformation you may need to do before
|
|---|
| 3951 | png_write_info(). In PNG files, the alpha channel in an image is the
|
|---|
| 3952 | level of opacity. If your data is supplied as a level of transparency,
|
|---|
| 3953 | you can invert the alpha channel before you write it, so that 0 is
|
|---|
| 3954 | fully transparent and 255 (in 8-bit or paletted images) or 65535
|
|---|
| 3955 | (in 16-bit images) is fully opaque, with
|
|---|
| 3956 |
|
|---|
| 3957 | png_set_invert_alpha(png_ptr);
|
|---|
| 3958 |
|
|---|
| 3959 | This must appear before png_write_info() instead of later with the
|
|---|
| 3960 | other transformations because in the case of paletted images the tRNS
|
|---|
| 3961 | chunk data has to be inverted before the tRNS chunk is written. If
|
|---|
| 3962 | your image is not a paletted image, the tRNS data (which in such cases
|
|---|
| 3963 | represents a single color to be rendered as transparent) won't need to
|
|---|
| 3964 | be changed, and you can safely do this transformation after your
|
|---|
| 3965 | png_write_info() call.
|
|---|
| 3966 |
|
|---|
| 3967 | If you need to write a private chunk that you want to appear before
|
|---|
| 3968 | the PLTE chunk when PLTE is present, you can write the PNG info in
|
|---|
| 3969 | two steps, and insert code to write your own chunk between them:
|
|---|
| 3970 |
|
|---|
| 3971 | png_write_info_before_PLTE(png_ptr, info_ptr);
|
|---|
| 3972 | png_set_unknown_chunks(png_ptr, info_ptr, ...);
|
|---|
| 3973 | png_write_info(png_ptr, info_ptr);
|
|---|
| 3974 |
|
|---|
| 3975 | After you've written the file information, you can set up the library
|
|---|
| 3976 | to handle any special transformations of the image data. The various
|
|---|
| 3977 | ways to transform the data will be described in the order that they
|
|---|
| 3978 | should occur. This is important, as some of these change the color
|
|---|
| 3979 | type and/or bit depth of the data, and some others only work on
|
|---|
| 3980 | certain color types and bit depths. Even though each transformation
|
|---|
| 3981 | checks to see if it has data that it can do something with, you should
|
|---|
| 3982 | make sure to only enable a transformation if it will be valid for the
|
|---|
| 3983 | data. For example, don't swap red and blue on grayscale data.
|
|---|
| 3984 |
|
|---|
| 3985 | PNG files store RGB pixels packed into 3 or 6 bytes. This code tells
|
|---|
| 3986 | the library to strip input data that has 4 or 8 bytes per pixel down
|
|---|
| 3987 | to 3 or 6 bytes (or strip 2 or 4-byte grayscale+filler data to 1 or 2
|
|---|
| 3988 | bytes per pixel).
|
|---|
| 3989 |
|
|---|
| 3990 | png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE);
|
|---|
| 3991 |
|
|---|
| 3992 | where the 0 is unused, and the location is either PNG_FILLER_BEFORE or
|
|---|
| 3993 | PNG_FILLER_AFTER, depending upon whether the filler byte in the pixel
|
|---|
| 3994 | is stored XRGB or RGBX.
|
|---|
| 3995 |
|
|---|
| 3996 | PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
|
|---|
| 3997 | they can, resulting in, for example, 8 pixels per byte for 1 bit files.
|
|---|
| 3998 | If the data is supplied at 1 pixel per byte, use this code, which will
|
|---|
| 3999 | correctly pack the pixels into a single byte:
|
|---|
| 4000 |
|
|---|
| 4001 | png_set_packing(png_ptr);
|
|---|
| 4002 |
|
|---|
| 4003 | PNG files reduce possible bit depths to 1, 2, 4, 8, and 16. If your
|
|---|
| 4004 | data is of another bit depth, you can write an sBIT chunk into the
|
|---|
| 4005 | file so that decoders can recover the original data if desired.
|
|---|
| 4006 |
|
|---|
| 4007 | /* Set the true bit depth of the image data */
|
|---|
| 4008 | if (color_type & PNG_COLOR_MASK_COLOR)
|
|---|
| 4009 | {
|
|---|
| 4010 | sig_bit.red = true_bit_depth;
|
|---|
| 4011 | sig_bit.green = true_bit_depth;
|
|---|
| 4012 | sig_bit.blue = true_bit_depth;
|
|---|
| 4013 | }
|
|---|
| 4014 |
|
|---|
| 4015 | else
|
|---|
| 4016 | {
|
|---|
| 4017 | sig_bit.gray = true_bit_depth;
|
|---|
| 4018 | }
|
|---|
| 4019 |
|
|---|
| 4020 | if (color_type & PNG_COLOR_MASK_ALPHA)
|
|---|
| 4021 | {
|
|---|
| 4022 | sig_bit.alpha = true_bit_depth;
|
|---|
| 4023 | }
|
|---|
| 4024 |
|
|---|
| 4025 | png_set_sBIT(png_ptr, info_ptr, &sig_bit);
|
|---|
| 4026 |
|
|---|
| 4027 | If the data is stored in the row buffer in a bit depth other than
|
|---|
| 4028 | one supported by PNG (e.g. 3 bit data in the range 0-7 for a 4-bit PNG),
|
|---|
| 4029 | this will scale the values to appear to be the correct bit depth as
|
|---|
| 4030 | is required by PNG.
|
|---|
| 4031 |
|
|---|
| 4032 | png_set_shift(png_ptr, &sig_bit);
|
|---|
| 4033 |
|
|---|
| 4034 | PNG files store 16-bit pixels in network byte order (big-endian,
|
|---|
| 4035 | ie. most significant bits first). This code would be used if they are
|
|---|
| 4036 | supplied the other way (little-endian, i.e. least significant bits
|
|---|
| 4037 | first, the way PCs store them):
|
|---|
| 4038 |
|
|---|
| 4039 | if (bit_depth > 8)
|
|---|
| 4040 | png_set_swap(png_ptr);
|
|---|
| 4041 |
|
|---|
| 4042 | If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
|
|---|
| 4043 | need to change the order the pixels are packed into bytes, you can use:
|
|---|
| 4044 |
|
|---|
| 4045 | if (bit_depth < 8)
|
|---|
| 4046 | png_set_packswap(png_ptr);
|
|---|
| 4047 |
|
|---|
| 4048 | PNG files store 3 color pixels in red, green, blue order. This code
|
|---|
| 4049 | would be used if they are supplied as blue, green, red:
|
|---|
| 4050 |
|
|---|
| 4051 | png_set_bgr(png_ptr);
|
|---|
| 4052 |
|
|---|
| 4053 | PNG files describe monochrome as black being zero and white being
|
|---|
| 4054 | one. This code would be used if the pixels are supplied with this reversed
|
|---|
| 4055 | (black being one and white being zero):
|
|---|
| 4056 |
|
|---|
| 4057 | png_set_invert_mono(png_ptr);
|
|---|
| 4058 |
|
|---|
| 4059 | Finally, you can write your own transformation function if none of
|
|---|
| 4060 | the existing ones meets your needs. This is done by setting a callback
|
|---|
| 4061 | with
|
|---|
| 4062 |
|
|---|
| 4063 | png_set_write_user_transform_fn(png_ptr,
|
|---|
| 4064 | write_transform_fn);
|
|---|
| 4065 |
|
|---|
| 4066 | You must supply the function
|
|---|
| 4067 |
|
|---|
| 4068 | void write_transform_fn(png_structp png_ptr, png_row_infop
|
|---|
| 4069 | row_info, png_bytep data)
|
|---|
| 4070 |
|
|---|
| 4071 | See pngtest.c for a working example. Your function will be called
|
|---|
| 4072 | before any of the other transformations are processed. If supported
|
|---|
| 4073 | libpng also supplies an information routine that may be called from
|
|---|
| 4074 | your callback:
|
|---|
| 4075 |
|
|---|
| 4076 | png_get_current_row_number(png_ptr);
|
|---|
| 4077 | png_get_current_pass_number(png_ptr);
|
|---|
| 4078 |
|
|---|
| 4079 | This returns the current row passed to the transform. With interlaced
|
|---|
| 4080 | images the value returned is the row in the input sub-image image. Use
|
|---|
| 4081 | PNG_ROW_FROM_PASS_ROW(row, pass) and PNG_COL_FROM_PASS_COL(col, pass) to
|
|---|
| 4082 | find the output pixel (x,y) given an interlaced sub-image pixel (row,col,pass).
|
|---|
| 4083 |
|
|---|
| 4084 | The discussion of interlace handling above contains more information on how to
|
|---|
| 4085 | use these values.
|
|---|
| 4086 |
|
|---|
| 4087 | You can also set up a pointer to a user structure for use by your
|
|---|
| 4088 | callback function.
|
|---|
| 4089 |
|
|---|
| 4090 | png_set_user_transform_info(png_ptr, user_ptr, 0, 0);
|
|---|
| 4091 |
|
|---|
| 4092 | The user_channels and user_depth parameters of this function are ignored
|
|---|
| 4093 | when writing; you can set them to zero as shown.
|
|---|
| 4094 |
|
|---|
| 4095 | You can retrieve the pointer via the function png_get_user_transform_ptr().
|
|---|
| 4096 | For example:
|
|---|
| 4097 |
|
|---|
| 4098 | voidp write_user_transform_ptr =
|
|---|
| 4099 | png_get_user_transform_ptr(png_ptr);
|
|---|
| 4100 |
|
|---|
| 4101 | It is possible to have libpng flush any pending output, either manually,
|
|---|
| 4102 | or automatically after a certain number of lines have been written. To
|
|---|
| 4103 | flush the output stream a single time call:
|
|---|
| 4104 |
|
|---|
| 4105 | png_write_flush(png_ptr);
|
|---|
| 4106 |
|
|---|
| 4107 | and to have libpng flush the output stream periodically after a certain
|
|---|
| 4108 | number of scanlines have been written, call:
|
|---|
| 4109 |
|
|---|
| 4110 | png_set_flush(png_ptr, nrows);
|
|---|
| 4111 |
|
|---|
| 4112 | Note that the distance between rows is from the last time png_write_flush()
|
|---|
| 4113 | was called, or the first row of the image if it has never been called.
|
|---|
| 4114 | So if you write 50 lines, and then png_set_flush 25, it will flush the
|
|---|
| 4115 | output on the next scanline, and every 25 lines thereafter, unless
|
|---|
| 4116 | png_write_flush() is called before 25 more lines have been written.
|
|---|
| 4117 | If nrows is too small (less than about 10 lines for a 640 pixel wide
|
|---|
| 4118 | RGB image) the image compression may decrease noticeably (although this
|
|---|
| 4119 | may be acceptable for real-time applications). Infrequent flushing will
|
|---|
| 4120 | only degrade the compression performance by a few percent over images
|
|---|
| 4121 | that do not use flushing.
|
|---|
| 4122 |
|
|---|
| 4123 | .SS Writing the image data
|
|---|
| 4124 |
|
|---|
| 4125 | That's it for the transformations. Now you can write the image data.
|
|---|
| 4126 | The simplest way to do this is in one function call. If you have the
|
|---|
| 4127 | whole image in memory, you can just call png_write_image() and libpng
|
|---|
| 4128 | will write the image. You will need to pass in an array of pointers to
|
|---|
| 4129 | each row. This function automatically handles interlacing, so you don't
|
|---|
| 4130 | need to call png_set_interlace_handling() or call this function multiple
|
|---|
| 4131 | times, or any of that other stuff necessary with png_write_rows().
|
|---|
| 4132 |
|
|---|
| 4133 | png_write_image(png_ptr, row_pointers);
|
|---|
| 4134 |
|
|---|
| 4135 | where row_pointers is:
|
|---|
| 4136 |
|
|---|
| 4137 | png_byte *row_pointers[height];
|
|---|
| 4138 |
|
|---|
| 4139 | You can point to void or char or whatever you use for pixels.
|
|---|
| 4140 |
|
|---|
| 4141 | If you don't want to write the whole image at once, you can
|
|---|
| 4142 | use png_write_rows() instead. If the file is not interlaced,
|
|---|
| 4143 | this is simple:
|
|---|
| 4144 |
|
|---|
| 4145 | png_write_rows(png_ptr, row_pointers,
|
|---|
| 4146 | number_of_rows);
|
|---|
| 4147 |
|
|---|
| 4148 | row_pointers is the same as in the png_write_image() call.
|
|---|
| 4149 |
|
|---|
| 4150 | If you are just writing one row at a time, you can do this with
|
|---|
| 4151 | a single row_pointer instead of an array of row_pointers:
|
|---|
| 4152 |
|
|---|
| 4153 | png_bytep row_pointer = row;
|
|---|
| 4154 |
|
|---|
| 4155 | png_write_row(png_ptr, row_pointer);
|
|---|
| 4156 |
|
|---|
| 4157 | When the file is interlaced, things can get a good deal more complicated.
|
|---|
| 4158 | The only currently (as of the PNG Specification version 1.2, dated July
|
|---|
| 4159 | 1999) defined interlacing scheme for PNG files is the "Adam7" interlace
|
|---|
| 4160 | scheme, that breaks down an image into seven smaller images of varying
|
|---|
| 4161 | size. libpng will build these images for you, or you can do them
|
|---|
| 4162 | yourself. If you want to build them yourself, see the PNG specification
|
|---|
| 4163 | for details of which pixels to write when.
|
|---|
| 4164 |
|
|---|
| 4165 | If you don't want libpng to handle the interlacing details, just
|
|---|
| 4166 | use png_set_interlace_handling() and call png_write_rows() the
|
|---|
| 4167 | correct number of times to write all the sub-images
|
|---|
| 4168 | (png_set_interlace_handling() returns the number of sub-images.)
|
|---|
| 4169 |
|
|---|
| 4170 | If you want libpng to build the sub-images, call this before you start
|
|---|
| 4171 | writing any rows:
|
|---|
| 4172 |
|
|---|
| 4173 | number_of_passes = png_set_interlace_handling(png_ptr);
|
|---|
| 4174 |
|
|---|
| 4175 | This will return the number of passes needed. Currently, this is seven,
|
|---|
| 4176 | but may change if another interlace type is added.
|
|---|
| 4177 |
|
|---|
| 4178 | Then write the complete image number_of_passes times.
|
|---|
| 4179 |
|
|---|
| 4180 | png_write_rows(png_ptr, row_pointers, number_of_rows);
|
|---|
| 4181 |
|
|---|
| 4182 | Think carefully before you write an interlaced image. Typically code that
|
|---|
| 4183 | reads such images reads all the image data into memory, uncompressed, before
|
|---|
| 4184 | doing any processing. Only code that can display an image on the fly can
|
|---|
| 4185 | take advantage of the interlacing and even then the image has to be exactly
|
|---|
| 4186 | the correct size for the output device, because scaling an image requires
|
|---|
| 4187 | adjacent pixels and these are not available until all the passes have been
|
|---|
| 4188 | read.
|
|---|
| 4189 |
|
|---|
| 4190 | If you do write an interlaced image you will hardly ever need to handle
|
|---|
| 4191 | the interlacing yourself. Call png_set_interlace_handling() and use the
|
|---|
| 4192 | approach described above.
|
|---|
| 4193 |
|
|---|
| 4194 | The only time it is conceivable that you will really need to write an
|
|---|
| 4195 | interlaced image pass-by-pass is when you have read one pass by pass and
|
|---|
| 4196 | made some pixel-by-pixel transformation to it, as described in the read
|
|---|
| 4197 | code above. In this case use the PNG_PASS_ROWS and PNG_PASS_COLS macros
|
|---|
| 4198 | to determine the size of each sub-image in turn and simply write the rows
|
|---|
| 4199 | you obtained from the read code.
|
|---|
| 4200 |
|
|---|
| 4201 | .SS Finishing a sequential write
|
|---|
| 4202 |
|
|---|
| 4203 | After you are finished writing the image, you should finish writing
|
|---|
| 4204 | the file. If you are interested in writing comments or time, you should
|
|---|
| 4205 | pass an appropriately filled png_info pointer. If you are not interested,
|
|---|
| 4206 | you can pass NULL.
|
|---|
| 4207 |
|
|---|
| 4208 | png_write_end(png_ptr, info_ptr);
|
|---|
| 4209 |
|
|---|
| 4210 | When you are done, you can free all memory used by libpng like this:
|
|---|
| 4211 |
|
|---|
| 4212 | png_destroy_write_struct(&png_ptr, &info_ptr);
|
|---|
| 4213 |
|
|---|
| 4214 | It is also possible to individually free the info_ptr members that
|
|---|
| 4215 | point to libpng-allocated storage with the following function:
|
|---|
| 4216 |
|
|---|
| 4217 | png_free_data(png_ptr, info_ptr, mask, seq)
|
|---|
| 4218 |
|
|---|
| 4219 | mask - identifies data to be freed, a mask
|
|---|
| 4220 | containing the bitwise OR of one or
|
|---|
| 4221 | more of
|
|---|
| 4222 | PNG_FREE_PLTE, PNG_FREE_TRNS,
|
|---|
| 4223 | PNG_FREE_HIST, PNG_FREE_ICCP,
|
|---|
| 4224 | PNG_FREE_PCAL, PNG_FREE_ROWS,
|
|---|
| 4225 | PNG_FREE_SCAL, PNG_FREE_SPLT,
|
|---|
| 4226 | PNG_FREE_TEXT, PNG_FREE_UNKN,
|
|---|
| 4227 | or simply PNG_FREE_ALL
|
|---|
| 4228 |
|
|---|
| 4229 | seq - sequence number of item to be freed
|
|---|
| 4230 | (\-1 for all items)
|
|---|
| 4231 |
|
|---|
| 4232 | This function may be safely called when the relevant storage has
|
|---|
| 4233 | already been freed, or has not yet been allocated, or was allocated
|
|---|
| 4234 | by the user and not by libpng, and will in those cases do nothing.
|
|---|
| 4235 | The "seq" parameter is ignored if only one item of the selected data
|
|---|
| 4236 | type, such as PLTE, is allowed. If "seq" is not \-1, and multiple items
|
|---|
| 4237 | are allowed for the data type identified in the mask, such as text or
|
|---|
| 4238 | sPLT, only the n'th item in the structure is freed, where n is "seq".
|
|---|
| 4239 |
|
|---|
| 4240 | If you allocated data such as a palette that you passed in to libpng
|
|---|
| 4241 | with png_set_*, you must not free it until just before the call to
|
|---|
| 4242 | png_destroy_write_struct().
|
|---|
| 4243 |
|
|---|
| 4244 | The default behavior is only to free data that was allocated internally
|
|---|
| 4245 | by libpng. This can be changed, so that libpng will not free the data,
|
|---|
| 4246 | or so that it will free data that was allocated by the user with png_malloc()
|
|---|
| 4247 | or png_calloc() and passed in via a png_set_*() function, with
|
|---|
| 4248 |
|
|---|
| 4249 | png_data_freer(png_ptr, info_ptr, freer, mask)
|
|---|
| 4250 |
|
|---|
| 4251 | freer - one of
|
|---|
| 4252 | PNG_DESTROY_WILL_FREE_DATA
|
|---|
| 4253 | PNG_SET_WILL_FREE_DATA
|
|---|
| 4254 | PNG_USER_WILL_FREE_DATA
|
|---|
| 4255 |
|
|---|
| 4256 | mask - which data elements are affected
|
|---|
| 4257 | same choices as in png_free_data()
|
|---|
| 4258 |
|
|---|
| 4259 | For example, to transfer responsibility for some data from a read structure
|
|---|
| 4260 | to a write structure, you could use
|
|---|
| 4261 |
|
|---|
| 4262 | png_data_freer(read_ptr, read_info_ptr,
|
|---|
| 4263 | PNG_USER_WILL_FREE_DATA,
|
|---|
| 4264 | PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
|
|---|
| 4265 |
|
|---|
| 4266 | png_data_freer(write_ptr, write_info_ptr,
|
|---|
| 4267 | PNG_DESTROY_WILL_FREE_DATA,
|
|---|
| 4268 | PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
|
|---|
| 4269 |
|
|---|
| 4270 | thereby briefly reassigning responsibility for freeing to the user but
|
|---|
| 4271 | immediately afterwards reassigning it once more to the write_destroy
|
|---|
| 4272 | function. Having done this, it would then be safe to destroy the read
|
|---|
| 4273 | structure and continue to use the PLTE, tRNS, and hIST data in the write
|
|---|
| 4274 | structure.
|
|---|
| 4275 |
|
|---|
| 4276 | This function only affects data that has already been allocated.
|
|---|
| 4277 | You can call this function before calling after the png_set_*() functions
|
|---|
| 4278 | to control whether the user or png_destroy_*() is supposed to free the data.
|
|---|
| 4279 | When the user assumes responsibility for libpng-allocated data, the
|
|---|
| 4280 | application must use
|
|---|
| 4281 | png_free() to free it, and when the user transfers responsibility to libpng
|
|---|
| 4282 | for data that the user has allocated, the user must have used png_malloc()
|
|---|
| 4283 | or png_calloc() to allocate it.
|
|---|
| 4284 |
|
|---|
| 4285 | If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
|
|---|
| 4286 | separately, do not transfer responsibility for freeing text_ptr to libpng,
|
|---|
| 4287 | because when libpng fills a png_text structure it combines these members with
|
|---|
| 4288 | the key member, and png_free_data() will free only text_ptr.key. Similarly,
|
|---|
| 4289 | if you transfer responsibility for free'ing text_ptr from libpng to your
|
|---|
| 4290 | application, your application must not separately free those members.
|
|---|
| 4291 | For a more compact example of writing a PNG image, see the file example.c.
|
|---|
| 4292 |
|
|---|
| 4293 | .SH V. Simplified API
|
|---|
| 4294 |
|
|---|
| 4295 | The simplified API, which became available in libpng-1.6.0, hides the details
|
|---|
| 4296 | of both libpng and the PNG file format itself.
|
|---|
| 4297 | It allows PNG files to be read into a very limited number of
|
|---|
| 4298 | in-memory bitmap formats or to be written from the same formats. If these
|
|---|
| 4299 | formats do not accommodate your needs then you can, and should, use the more
|
|---|
| 4300 | sophisticated APIs above - these support a wide variety of in-memory formats
|
|---|
| 4301 | and a wide variety of sophisticated transformations to those formats as well
|
|---|
| 4302 | as a wide variety of APIs to manipulate ancillary information.
|
|---|
| 4303 |
|
|---|
| 4304 | To read a PNG file using the simplified API:
|
|---|
| 4305 |
|
|---|
| 4306 | 1) Declare a 'png_image' structure (see below) on the stack, set the
|
|---|
| 4307 | version field to PNG_IMAGE_VERSION and the 'opaque' pointer to NULL
|
|---|
| 4308 | (this is REQUIRED, your program may crash if you don't do it.)
|
|---|
| 4309 |
|
|---|
| 4310 | 2) Call the appropriate png_image_begin_read... function.
|
|---|
| 4311 |
|
|---|
| 4312 | 3) Set the png_image 'format' member to the required sample format.
|
|---|
| 4313 |
|
|---|
| 4314 | 4) Allocate a buffer for the image and, if required, the color-map.
|
|---|
| 4315 |
|
|---|
| 4316 | 5) Call png_image_finish_read to read the image and, if required, the
|
|---|
| 4317 | color-map into your buffers.
|
|---|
| 4318 |
|
|---|
| 4319 | There are no restrictions on the format of the PNG input itself; all valid
|
|---|
| 4320 | color types, bit depths, and interlace methods are acceptable, and the
|
|---|
| 4321 | input image is transformed as necessary to the requested in-memory format
|
|---|
| 4322 | during the png_image_finish_read() step. The only caveat is that if you
|
|---|
| 4323 | request a color-mapped image from a PNG that is full-color or makes
|
|---|
| 4324 | complex use of an alpha channel the transformation is extremely lossy and the
|
|---|
| 4325 | result may look terrible.
|
|---|
| 4326 |
|
|---|
| 4327 | To write a PNG file using the simplified API:
|
|---|
| 4328 |
|
|---|
| 4329 | 1) Declare a 'png_image' structure on the stack and memset()
|
|---|
| 4330 | it to all zero.
|
|---|
| 4331 |
|
|---|
| 4332 | 2) Initialize the members of the structure that describe the
|
|---|
| 4333 | image, setting the 'format' member to the format of the
|
|---|
| 4334 | image samples.
|
|---|
| 4335 |
|
|---|
| 4336 | 3) Call the appropriate png_image_write... function with a
|
|---|
| 4337 | pointer to the image and, if necessary, the color-map to write
|
|---|
| 4338 | the PNG data.
|
|---|
| 4339 |
|
|---|
| 4340 | png_image is a structure that describes the in-memory format of an image
|
|---|
| 4341 | when it is being read or defines the in-memory format of an image that you
|
|---|
| 4342 | need to write. The "png_image" structure contains the following members:
|
|---|
| 4343 |
|
|---|
| 4344 | png_controlp opaque Initialize to NULL, free with png_image_free
|
|---|
| 4345 | png_uint_32 version Set to PNG_IMAGE_VERSION
|
|---|
| 4346 | png_uint_32 width Image width in pixels (columns)
|
|---|
| 4347 | png_uint_32 height Image height in pixels (rows)
|
|---|
| 4348 | png_uint_32 format Image format as defined below
|
|---|
| 4349 | png_uint_32 flags A bit mask containing informational flags
|
|---|
| 4350 | png_uint_32 colormap_entries; Number of entries in the color-map
|
|---|
| 4351 | png_uint_32 warning_or_error;
|
|---|
| 4352 | char message[64];
|
|---|
| 4353 |
|
|---|
| 4354 | In the event of an error or warning the "warning_or_error"
|
|---|
| 4355 | field will be set to a non-zero value and the 'message' field will contain
|
|---|
| 4356 | a '\0' terminated string with the libpng error or warning message. If both
|
|---|
| 4357 | warnings and an error were encountered, only the error is recorded. If there
|
|---|
| 4358 | are multiple warnings, only the first one is recorded.
|
|---|
| 4359 |
|
|---|
| 4360 | The upper 30 bits of the "warning_or_error" value are reserved; the low two
|
|---|
| 4361 | bits contain a two bit code such that a value more than 1 indicates a failure
|
|---|
| 4362 | in the API just called:
|
|---|
| 4363 |
|
|---|
| 4364 | 0 - no warning or error
|
|---|
| 4365 | 1 - warning
|
|---|
| 4366 | 2 - error
|
|---|
| 4367 | 3 - error preceded by warning
|
|---|
| 4368 |
|
|---|
| 4369 | The pixels (samples) of the image have one to four channels whose components
|
|---|
| 4370 | have original values in the range 0 to 1.0:
|
|---|
| 4371 |
|
|---|
| 4372 | 1: A single gray or luminance channel (G).
|
|---|
| 4373 | 2: A gray/luminance channel and an alpha channel (GA).
|
|---|
| 4374 | 3: Three red, green, blue color channels (RGB).
|
|---|
| 4375 | 4: Three color channels and an alpha channel (RGBA).
|
|---|
| 4376 |
|
|---|
| 4377 | The channels are encoded in one of two ways:
|
|---|
| 4378 |
|
|---|
| 4379 | a) As a small integer, value 0..255, contained in a single byte. For the
|
|---|
| 4380 | alpha channel the original value is simply value/255. For the color or
|
|---|
| 4381 | luminance channels the value is encoded according to the sRGB specification
|
|---|
| 4382 | and matches the 8-bit format expected by typical display devices.
|
|---|
| 4383 |
|
|---|
| 4384 | The color/gray channels are not scaled (pre-multiplied) by the alpha
|
|---|
| 4385 | channel and are suitable for passing to color management software.
|
|---|
| 4386 |
|
|---|
| 4387 | b) As a value in the range 0..65535, contained in a 2-byte integer, in
|
|---|
| 4388 | the native byte order of the platform on which the application is running.
|
|---|
| 4389 | All channels can be converted to the original value by dividing by 65535; all
|
|---|
| 4390 | channels are linear. Color channels use the RGB encoding (RGB end-points) of
|
|---|
| 4391 | the sRGB specification. This encoding is identified by the
|
|---|
| 4392 | PNG_FORMAT_FLAG_LINEAR flag below.
|
|---|
| 4393 |
|
|---|
| 4394 | When the simplified API needs to convert between sRGB and linear colorspaces,
|
|---|
| 4395 | the actual sRGB transfer curve defined in the sRGB specification (see the
|
|---|
| 4396 | article at https://en.wikipedia.org/wiki/SRGB) is used, not the gamma=1/2.2
|
|---|
| 4397 | approximation used elsewhere in libpng.
|
|---|
| 4398 |
|
|---|
| 4399 | When an alpha channel is present it is expected to denote pixel coverage
|
|---|
| 4400 | of the color or luminance channels and is returned as an associated alpha
|
|---|
| 4401 | channel: the color/gray channels are scaled (pre-multiplied) by the alpha
|
|---|
| 4402 | value.
|
|---|
| 4403 |
|
|---|
| 4404 | The samples are either contained directly in the image data, between 1 and 8
|
|---|
| 4405 | bytes per pixel according to the encoding, or are held in a color-map indexed
|
|---|
| 4406 | by bytes in the image data. In the case of a color-map the color-map entries
|
|---|
| 4407 | are individual samples, encoded as above, and the image data has one byte per
|
|---|
| 4408 | pixel to select the relevant sample from the color-map.
|
|---|
| 4409 |
|
|---|
| 4410 | PNG_FORMAT_*
|
|---|
| 4411 |
|
|---|
| 4412 | The #defines to be used in png_image::format. Each #define identifies a
|
|---|
| 4413 | particular layout of channel data and, if present, alpha values. There are
|
|---|
| 4414 | separate defines for each of the two component encodings.
|
|---|
| 4415 |
|
|---|
| 4416 | A format is built up using single bit flag values. All combinations are
|
|---|
| 4417 | valid. Formats can be built up from the flag values or you can use one of
|
|---|
| 4418 | the predefined values below. When testing formats always use the FORMAT_FLAG
|
|---|
| 4419 | macros to test for individual features - future versions of the library may
|
|---|
| 4420 | add new flags.
|
|---|
| 4421 |
|
|---|
| 4422 | When reading or writing color-mapped images the format should be set to the
|
|---|
| 4423 | format of the entries in the color-map then png_image_{read,write}_colormap
|
|---|
| 4424 | called to read or write the color-map and set the format correctly for the
|
|---|
| 4425 | image data. Do not set the PNG_FORMAT_FLAG_COLORMAP bit directly!
|
|---|
| 4426 |
|
|---|
| 4427 | NOTE: libpng can be built with particular features disabled. If you see
|
|---|
| 4428 | compiler errors because the definition of one of the following flags has been
|
|---|
| 4429 | compiled out it is because libpng does not have the required support. It is
|
|---|
| 4430 | possible, however, for the libpng configuration to enable the format on just
|
|---|
| 4431 | read or just write; in that case you may see an error at run time.
|
|---|
| 4432 | You can guard against this by checking for the definition of the
|
|---|
| 4433 | appropriate "_SUPPORTED" macro, one of:
|
|---|
| 4434 |
|
|---|
| 4435 | PNG_SIMPLIFIED_{READ,WRITE}_{BGR,AFIRST}_SUPPORTED
|
|---|
| 4436 |
|
|---|
| 4437 | PNG_FORMAT_FLAG_ALPHA format with an alpha channel
|
|---|
| 4438 | PNG_FORMAT_FLAG_COLOR color format: otherwise grayscale
|
|---|
| 4439 | PNG_FORMAT_FLAG_LINEAR 2-byte channels else 1-byte
|
|---|
| 4440 | PNG_FORMAT_FLAG_COLORMAP image data is color-mapped
|
|---|
| 4441 | PNG_FORMAT_FLAG_BGR BGR colors, else order is RGB
|
|---|
| 4442 | PNG_FORMAT_FLAG_AFIRST alpha channel comes first
|
|---|
| 4443 |
|
|---|
| 4444 | Supported formats are as follows. Future versions of libpng may support more
|
|---|
| 4445 | formats; for compatibility with older versions simply check if the format
|
|---|
| 4446 | macro is defined using #ifdef. These defines describe the in-memory layout
|
|---|
| 4447 | of the components of the pixels of the image.
|
|---|
| 4448 |
|
|---|
| 4449 | First the single byte (sRGB) formats:
|
|---|
| 4450 |
|
|---|
| 4451 | PNG_FORMAT_GRAY
|
|---|
| 4452 | PNG_FORMAT_GA
|
|---|
| 4453 | PNG_FORMAT_AG
|
|---|
| 4454 | PNG_FORMAT_RGB
|
|---|
| 4455 | PNG_FORMAT_BGR
|
|---|
| 4456 | PNG_FORMAT_RGBA
|
|---|
| 4457 | PNG_FORMAT_ARGB
|
|---|
| 4458 | PNG_FORMAT_BGRA
|
|---|
| 4459 | PNG_FORMAT_ABGR
|
|---|
| 4460 |
|
|---|
| 4461 | Then the linear 2-byte formats. When naming these "Y" is used to
|
|---|
| 4462 | indicate a luminance (gray) channel. The component order within the pixel
|
|---|
| 4463 | is always the same - there is no provision for swapping the order of the
|
|---|
| 4464 | components in the linear format. The components are 16-bit integers in
|
|---|
| 4465 | the native byte order for your platform, and there is no provision for
|
|---|
| 4466 | swapping the bytes to a different endian condition.
|
|---|
| 4467 |
|
|---|
| 4468 | PNG_FORMAT_LINEAR_Y
|
|---|
| 4469 | PNG_FORMAT_LINEAR_Y_ALPHA
|
|---|
| 4470 | PNG_FORMAT_LINEAR_RGB
|
|---|
| 4471 | PNG_FORMAT_LINEAR_RGB_ALPHA
|
|---|
| 4472 |
|
|---|
| 4473 | With color-mapped formats the image data is one byte for each pixel. The byte
|
|---|
| 4474 | is an index into the color-map which is formatted as above. To obtain a
|
|---|
| 4475 | color-mapped format it is sufficient just to add the PNG_FOMAT_FLAG_COLORMAP
|
|---|
| 4476 | to one of the above definitions, or you can use one of the definitions below.
|
|---|
| 4477 |
|
|---|
| 4478 | PNG_FORMAT_RGB_COLORMAP
|
|---|
| 4479 | PNG_FORMAT_BGR_COLORMAP
|
|---|
| 4480 | PNG_FORMAT_RGBA_COLORMAP
|
|---|
| 4481 | PNG_FORMAT_ARGB_COLORMAP
|
|---|
| 4482 | PNG_FORMAT_BGRA_COLORMAP
|
|---|
| 4483 | PNG_FORMAT_ABGR_COLORMAP
|
|---|
| 4484 |
|
|---|
| 4485 | PNG_IMAGE macros
|
|---|
| 4486 |
|
|---|
| 4487 | These are convenience macros to derive information from a png_image
|
|---|
| 4488 | structure. The PNG_IMAGE_SAMPLE_ macros return values appropriate to the
|
|---|
| 4489 | actual image sample values - either the entries in the color-map or the
|
|---|
| 4490 | pixels in the image. The PNG_IMAGE_PIXEL_ macros return corresponding values
|
|---|
| 4491 | for the pixels and will always return 1 for color-mapped formats. The
|
|---|
| 4492 | remaining macros return information about the rows in the image and the
|
|---|
| 4493 | complete image.
|
|---|
| 4494 |
|
|---|
| 4495 | NOTE: All the macros that take a png_image::format parameter are compile time
|
|---|
| 4496 | constants if the format parameter is, itself, a constant. Therefore these
|
|---|
| 4497 | macros can be used in array declarations and case labels where required.
|
|---|
| 4498 | Similarly the macros are also pre-processor constants (sizeof is not used) so
|
|---|
| 4499 | they can be used in #if tests.
|
|---|
| 4500 |
|
|---|
| 4501 | PNG_IMAGE_SAMPLE_CHANNELS(fmt)
|
|---|
| 4502 | Returns the total number of channels in a given format: 1..4
|
|---|
| 4503 |
|
|---|
| 4504 | PNG_IMAGE_SAMPLE_COMPONENT_SIZE(fmt)
|
|---|
| 4505 | Returns the size in bytes of a single component of a pixel or color-map
|
|---|
| 4506 | entry (as appropriate) in the image: 1 or 2.
|
|---|
| 4507 |
|
|---|
| 4508 | PNG_IMAGE_SAMPLE_SIZE(fmt)
|
|---|
| 4509 | This is the size of the sample data for one sample. If the image is
|
|---|
| 4510 | color-mapped it is the size of one color-map entry (and image pixels are
|
|---|
| 4511 | one byte in size), otherwise it is the size of one image pixel.
|
|---|
| 4512 |
|
|---|
| 4513 | PNG_IMAGE_MAXIMUM_COLORMAP_COMPONENTS(fmt)
|
|---|
| 4514 | The maximum size of the color-map required by the format expressed in a
|
|---|
| 4515 | count of components. This can be used to compile-time allocate a
|
|---|
| 4516 | color-map:
|
|---|
| 4517 |
|
|---|
| 4518 | png_uint_16 colormap[PNG_IMAGE_MAXIMUM_COLORMAP_COMPONENTS(linear_fmt)];
|
|---|
| 4519 |
|
|---|
| 4520 | png_byte colormap[PNG_IMAGE_MAXIMUM_COLORMAP_COMPONENTS(sRGB_fmt)];
|
|---|
| 4521 |
|
|---|
| 4522 | Alternatively use the PNG_IMAGE_COLORMAP_SIZE macro below to use the
|
|---|
| 4523 | information from one of the png_image_begin_read_ APIs and dynamically
|
|---|
| 4524 | allocate the required memory.
|
|---|
| 4525 |
|
|---|
| 4526 | PNG_IMAGE_COLORMAP_SIZE(fmt)
|
|---|
| 4527 | The size of the color-map required by the format; this is the size of the
|
|---|
| 4528 | color-map buffer passed to the png_image_{read,write}_colormap APIs. It is
|
|---|
| 4529 | a fixed number determined by the format so can easily be allocated on the
|
|---|
| 4530 | stack if necessary.
|
|---|
| 4531 |
|
|---|
| 4532 | Corresponding information about the pixels
|
|---|
| 4533 |
|
|---|
| 4534 | PNG_IMAGE_PIXEL_CHANNELS(fmt)
|
|---|
| 4535 | The number of separate channels (components) in a pixel; 1 for a
|
|---|
| 4536 | color-mapped image.
|
|---|
| 4537 |
|
|---|
| 4538 | PNG_IMAGE_PIXEL_COMPONENT_SIZE(fmt)\
|
|---|
| 4539 | The size, in bytes, of each component in a pixel; 1 for a color-mapped
|
|---|
| 4540 | image.
|
|---|
| 4541 |
|
|---|
| 4542 | PNG_IMAGE_PIXEL_SIZE(fmt)
|
|---|
| 4543 | The size, in bytes, of a complete pixel; 1 for a color-mapped image.
|
|---|
| 4544 |
|
|---|
| 4545 | Information about the whole row, or whole image
|
|---|
| 4546 |
|
|---|
| 4547 | PNG_IMAGE_ROW_STRIDE(image)
|
|---|
| 4548 | Returns the total number of components in a single row of the image; this
|
|---|
| 4549 | is the minimum 'row stride', the minimum count of components between each
|
|---|
| 4550 | row. For a color-mapped image this is the minimum number of bytes in a
|
|---|
| 4551 | row.
|
|---|
| 4552 |
|
|---|
| 4553 | If you need the stride measured in bytes, row_stride_bytes is
|
|---|
| 4554 | PNG_IMAGE_ROW_STRIDE(image) * PNG_IMAGE_PIXEL_COMPONENT_SIZE(fmt)
|
|---|
| 4555 | plus any padding bytes that your application might need, for example
|
|---|
| 4556 | to start the next row on a 4-byte boundary.
|
|---|
| 4557 |
|
|---|
| 4558 | PNG_IMAGE_BUFFER_SIZE(image, row_stride)
|
|---|
| 4559 | Return the size, in bytes, of an image buffer given a png_image and a row
|
|---|
| 4560 | stride - the number of components to leave space for in each row.
|
|---|
| 4561 |
|
|---|
| 4562 | PNG_IMAGE_SIZE(image)
|
|---|
| 4563 | Return the size, in bytes, of the image in memory given just a png_image;
|
|---|
| 4564 | the row stride is the minimum stride required for the image.
|
|---|
| 4565 |
|
|---|
| 4566 | PNG_IMAGE_COLORMAP_SIZE(image)
|
|---|
| 4567 | Return the size, in bytes, of the color-map of this image. If the image
|
|---|
| 4568 | format is not a color-map format this will return a size sufficient for
|
|---|
| 4569 | 256 entries in the given format; check PNG_FORMAT_FLAG_COLORMAP if
|
|---|
| 4570 | you don't want to allocate a color-map in this case.
|
|---|
| 4571 |
|
|---|
| 4572 | PNG_IMAGE_FLAG_*
|
|---|
| 4573 |
|
|---|
| 4574 | Flags containing additional information about the image are held in
|
|---|
| 4575 | the 'flags' field of png_image.
|
|---|
| 4576 |
|
|---|
| 4577 | PNG_IMAGE_FLAG_COLORSPACE_NOT_sRGB == 0x01
|
|---|
| 4578 | This indicates that the RGB values of the in-memory bitmap do not
|
|---|
| 4579 | correspond to the red, green and blue end-points defined by sRGB.
|
|---|
| 4580 |
|
|---|
| 4581 | PNG_IMAGE_FLAG_FAST == 0x02
|
|---|
| 4582 | On write emphasise speed over compression; the resultant PNG file will be
|
|---|
| 4583 | larger but will be produced significantly faster, particular for large
|
|---|
| 4584 | images. Do not use this option for images which will be distributed, only
|
|---|
| 4585 | used it when producing intermediate files that will be read back in
|
|---|
| 4586 | repeatedly. For a typical 24-bit image the option will double the read
|
|---|
| 4587 | speed at the cost of increasing the image size by 25%, however for many
|
|---|
| 4588 | more compressible images the PNG file can be 10 times larger with only a
|
|---|
| 4589 | slight speed gain.
|
|---|
| 4590 |
|
|---|
| 4591 | PNG_IMAGE_FLAG_16BIT_sRGB == 0x04
|
|---|
| 4592 | On read if the image is a 16-bit per component image and there is no gAMA
|
|---|
| 4593 | or sRGB chunk assume that the components are sRGB encoded. Notice that
|
|---|
| 4594 | images output by the simplified API always have gamma information; setting
|
|---|
| 4595 | this flag only affects the interpretation of 16-bit images from an
|
|---|
| 4596 | external source. It is recommended that the application expose this flag
|
|---|
| 4597 | to the user; the user can normally easily recognize the difference between
|
|---|
| 4598 | linear and sRGB encoding. This flag has no effect on write - the data
|
|---|
| 4599 | passed to the write APIs must have the correct encoding (as defined
|
|---|
| 4600 | above.)
|
|---|
| 4601 |
|
|---|
| 4602 | If the flag is not set (the default) input 16-bit per component data is
|
|---|
| 4603 | assumed to be linear.
|
|---|
| 4604 |
|
|---|
| 4605 | NOTE: the flag can only be set after the png_image_begin_read_ call,
|
|---|
| 4606 | because that call initializes the 'flags' field.
|
|---|
| 4607 |
|
|---|
| 4608 | READ APIs
|
|---|
| 4609 |
|
|---|
| 4610 | The png_image passed to the read APIs must have been initialized by setting
|
|---|
| 4611 | the png_controlp field 'opaque' to NULL (or, better, memset the whole thing.)
|
|---|
| 4612 |
|
|---|
| 4613 | int png_image_begin_read_from_file( png_imagep image,
|
|---|
| 4614 | const char *file_name)
|
|---|
| 4615 |
|
|---|
| 4616 | The named file is opened for read and the image header
|
|---|
| 4617 | is filled in from the PNG header in the file.
|
|---|
| 4618 |
|
|---|
| 4619 | int png_image_begin_read_from_stdio (png_imagep image,
|
|---|
| 4620 | FILE* file)
|
|---|
| 4621 |
|
|---|
| 4622 | The PNG header is read from the stdio FILE object.
|
|---|
| 4623 |
|
|---|
| 4624 | int png_image_begin_read_from_memory(png_imagep image,
|
|---|
| 4625 | png_const_voidp memory, size_t size)
|
|---|
| 4626 |
|
|---|
| 4627 | The PNG header is read from the given memory buffer.
|
|---|
| 4628 |
|
|---|
| 4629 | int png_image_finish_read(png_imagep image,
|
|---|
| 4630 | png_colorp background, void *buffer,
|
|---|
| 4631 | png_int_32 row_stride, void *colormap));
|
|---|
| 4632 |
|
|---|
| 4633 | Finish reading the image into the supplied buffer and
|
|---|
| 4634 | clean up the png_image structure.
|
|---|
| 4635 |
|
|---|
| 4636 | row_stride is the step, in png_byte or png_uint_16 units
|
|---|
| 4637 | as appropriate, between adjacent rows. A positive stride
|
|---|
| 4638 | indicates that the top-most row is first in the buffer -
|
|---|
| 4639 | the normal top-down arrangement. A negative stride
|
|---|
| 4640 | indicates that the bottom-most row is first in the buffer.
|
|---|
| 4641 |
|
|---|
| 4642 | background need only be supplied if an alpha channel must
|
|---|
| 4643 | be removed from a png_byte format and the removal is to be
|
|---|
| 4644 | done by compositing on a solid color; otherwise it may be
|
|---|
| 4645 | NULL and any composition will be done directly onto the
|
|---|
| 4646 | buffer. The value is an sRGB color to use for the
|
|---|
| 4647 | background, for grayscale output the green channel is used.
|
|---|
| 4648 |
|
|---|
| 4649 | For linear output removing the alpha channel is always done
|
|---|
| 4650 | by compositing on black.
|
|---|
| 4651 |
|
|---|
| 4652 | void png_image_free(png_imagep image)
|
|---|
| 4653 |
|
|---|
| 4654 | Free any data allocated by libpng in image->opaque,
|
|---|
| 4655 | setting the pointer to NULL. May be called at any time
|
|---|
| 4656 | after the structure is initialized.
|
|---|
| 4657 |
|
|---|
| 4658 | When the simplified API needs to convert between sRGB and linear colorspaces,
|
|---|
| 4659 | the actual sRGB transfer curve defined in the sRGB specification (see the
|
|---|
| 4660 | article at https://en.wikipedia.org/wiki/SRGB) is used, not the gamma=1/2.2
|
|---|
| 4661 | approximation used elsewhere in libpng.
|
|---|
| 4662 |
|
|---|
| 4663 | WRITE APIS
|
|---|
| 4664 |
|
|---|
| 4665 | For write you must initialize a png_image structure to describe the image to
|
|---|
| 4666 | be written:
|
|---|
| 4667 |
|
|---|
| 4668 | version: must be set to PNG_IMAGE_VERSION
|
|---|
| 4669 | opaque: must be initialized to NULL
|
|---|
| 4670 | width: image width in pixels
|
|---|
| 4671 | height: image height in rows
|
|---|
| 4672 | format: the format of the data you wish to write
|
|---|
| 4673 | flags: set to 0 unless one of the defined flags applies; set
|
|---|
| 4674 | PNG_IMAGE_FLAG_COLORSPACE_NOT_sRGB for color format images
|
|---|
| 4675 | where the RGB values do not correspond to the colors in sRGB.
|
|---|
| 4676 | colormap_entries: set to the number of entries in the color-map (0 to 256)
|
|---|
| 4677 |
|
|---|
| 4678 | int png_image_write_to_file, (png_imagep image,
|
|---|
| 4679 | const char *file, int convert_to_8bit, const void *buffer,
|
|---|
| 4680 | png_int_32 row_stride, const void *colormap));
|
|---|
| 4681 |
|
|---|
| 4682 | Write the image to the named file.
|
|---|
| 4683 |
|
|---|
| 4684 | int png_image_write_to_memory (png_imagep image, void *memory,
|
|---|
| 4685 | png_alloc_size_t * PNG_RESTRICT memory_bytes,
|
|---|
| 4686 | int convert_to_8_bit, const void *buffer, ptrdiff_t row_stride,
|
|---|
| 4687 | const void *colormap));
|
|---|
| 4688 |
|
|---|
| 4689 | Write the image to memory.
|
|---|
| 4690 |
|
|---|
| 4691 | int png_image_write_to_stdio(png_imagep image, FILE *file,
|
|---|
| 4692 | int convert_to_8_bit, const void *buffer,
|
|---|
| 4693 | png_int_32 row_stride, const void *colormap)
|
|---|
| 4694 |
|
|---|
| 4695 | Write the image to the given (FILE*).
|
|---|
| 4696 |
|
|---|
| 4697 | With all write APIs if image is in one of the linear formats with
|
|---|
| 4698 | (png_uint_16) data then setting convert_to_8_bit will cause the output to be
|
|---|
| 4699 | a (png_byte) PNG gamma encoded according to the sRGB specification, otherwise
|
|---|
| 4700 | a 16-bit linear encoded PNG file is written.
|
|---|
| 4701 |
|
|---|
| 4702 | With all APIs row_stride is handled as in the read APIs - it is the spacing
|
|---|
| 4703 | from one row to the next in component sized units (float) and if negative
|
|---|
| 4704 | indicates a bottom-up row layout in the buffer. If you pass zero, libpng will
|
|---|
| 4705 | calculate the row_stride for you from the width and number of channels.
|
|---|
| 4706 |
|
|---|
| 4707 | Note that the write API does not support interlacing, sub-8-bit pixels,
|
|---|
| 4708 | indexed (paletted) images, or most ancillary chunks.
|
|---|
| 4709 |
|
|---|
| 4710 | .SH VI. Modifying/Customizing libpng
|
|---|
| 4711 |
|
|---|
| 4712 | There are two issues here. The first is changing how libpng does
|
|---|
| 4713 | standard things like memory allocation, input/output, and error handling.
|
|---|
| 4714 | The second deals with more complicated things like adding new chunks,
|
|---|
| 4715 | adding new transformations, and generally changing how libpng works.
|
|---|
| 4716 | Both of those are compile-time issues; that is, they are generally
|
|---|
| 4717 | determined at the time the code is written, and there is rarely a need
|
|---|
| 4718 | to provide the user with a means of changing them.
|
|---|
| 4719 |
|
|---|
| 4720 | Memory allocation, input/output, and error handling
|
|---|
| 4721 |
|
|---|
| 4722 | All of the memory allocation, input/output, and error handling in libpng
|
|---|
| 4723 | goes through callbacks that are user-settable. The default routines are
|
|---|
| 4724 | in pngmem.c, pngrio.c, pngwio.c, and pngerror.c, respectively. To change
|
|---|
| 4725 | these functions, call the appropriate png_set_*_fn() function.
|
|---|
| 4726 |
|
|---|
| 4727 | Memory allocation is done through the functions png_malloc(), png_calloc(),
|
|---|
| 4728 | and png_free(). The png_malloc() and png_free() functions currently just
|
|---|
| 4729 | call the standard C functions and png_calloc() calls png_malloc() and then
|
|---|
| 4730 | clears the newly allocated memory to zero; note that png_calloc(png_ptr, size)
|
|---|
| 4731 | is not the same as the calloc(number, size) function provided by stdlib.h.
|
|---|
| 4732 | There is limited support for certain systems with segmented memory
|
|---|
| 4733 | architectures and the types of pointers declared by png.h match this; you
|
|---|
| 4734 | will have to use appropriate pointers in your application. If you prefer
|
|---|
| 4735 | to use a different method of allocating and freeing data, you can use
|
|---|
| 4736 | png_create_read_struct_2() or png_create_write_struct_2() to register your
|
|---|
| 4737 | own functions as described above. These functions also provide a void
|
|---|
| 4738 | pointer that can be retrieved via
|
|---|
| 4739 |
|
|---|
| 4740 | mem_ptr=png_get_mem_ptr(png_ptr);
|
|---|
| 4741 |
|
|---|
| 4742 | Your replacement memory functions must have prototypes as follows:
|
|---|
| 4743 |
|
|---|
| 4744 | png_voidp malloc_fn(png_structp png_ptr,
|
|---|
| 4745 | png_alloc_size_t size);
|
|---|
| 4746 |
|
|---|
| 4747 | void free_fn(png_structp png_ptr, png_voidp ptr);
|
|---|
| 4748 |
|
|---|
| 4749 | Your malloc_fn() must return NULL in case of failure. The png_malloc()
|
|---|
| 4750 | function will normally call png_error() if it receives a NULL from the
|
|---|
| 4751 | system memory allocator or from your replacement malloc_fn().
|
|---|
| 4752 |
|
|---|
| 4753 | Your free_fn() will never be called with a NULL ptr, since libpng's
|
|---|
| 4754 | png_free() checks for NULL before calling free_fn().
|
|---|
| 4755 |
|
|---|
| 4756 | Input/Output in libpng is done through png_read() and png_write(),
|
|---|
| 4757 | which currently just call fread() and fwrite(). The FILE * is stored in
|
|---|
| 4758 | png_struct and is initialized via png_init_io(). If you wish to change
|
|---|
| 4759 | the method of I/O, the library supplies callbacks that you can set
|
|---|
| 4760 | through the function png_set_read_fn() and png_set_write_fn() at run
|
|---|
| 4761 | time, instead of calling the png_init_io() function. These functions
|
|---|
| 4762 | also provide a void pointer that can be retrieved via the function
|
|---|
| 4763 | png_get_io_ptr(). For example:
|
|---|
| 4764 |
|
|---|
| 4765 | png_set_read_fn(png_structp read_ptr,
|
|---|
| 4766 | voidp read_io_ptr, png_rw_ptr read_data_fn)
|
|---|
| 4767 |
|
|---|
| 4768 | png_set_write_fn(png_structp write_ptr,
|
|---|
| 4769 | voidp write_io_ptr, png_rw_ptr write_data_fn,
|
|---|
| 4770 | png_flush_ptr output_flush_fn);
|
|---|
| 4771 |
|
|---|
| 4772 | voidp read_io_ptr = png_get_io_ptr(read_ptr);
|
|---|
| 4773 | voidp write_io_ptr = png_get_io_ptr(write_ptr);
|
|---|
| 4774 |
|
|---|
| 4775 | The replacement I/O functions must have prototypes as follows:
|
|---|
| 4776 |
|
|---|
| 4777 | void user_read_data(png_structp png_ptr,
|
|---|
| 4778 | png_bytep data, size_t length);
|
|---|
| 4779 |
|
|---|
| 4780 | void user_write_data(png_structp png_ptr,
|
|---|
| 4781 | png_bytep data, size_t length);
|
|---|
| 4782 |
|
|---|
| 4783 | void user_flush_data(png_structp png_ptr);
|
|---|
| 4784 |
|
|---|
| 4785 | The user_read_data() function is responsible for detecting and
|
|---|
| 4786 | handling end-of-data errors.
|
|---|
| 4787 |
|
|---|
| 4788 | Supplying NULL for the read, write, or flush functions sets them back
|
|---|
| 4789 | to using the default C stream functions, which expect the io_ptr to
|
|---|
| 4790 | point to a standard *FILE structure. It is probably a mistake
|
|---|
| 4791 | to use NULL for one of write_data_fn and output_flush_fn but not both
|
|---|
| 4792 | of them, unless you have built libpng with PNG_NO_WRITE_FLUSH defined.
|
|---|
| 4793 | It is an error to read from a write stream, and vice versa.
|
|---|
| 4794 |
|
|---|
| 4795 | Error handling in libpng is done through png_error() and png_warning().
|
|---|
| 4796 | Errors handled through png_error() are fatal, meaning that png_error()
|
|---|
| 4797 | should never return to its caller. Currently, this is handled via
|
|---|
| 4798 | setjmp() and longjmp() (unless you have compiled libpng with
|
|---|
| 4799 | PNG_NO_SETJMP, in which case it is handled via PNG_ABORT()),
|
|---|
| 4800 | but you could change this to do things like exit() if you should wish,
|
|---|
| 4801 | as long as your function does not return.
|
|---|
| 4802 |
|
|---|
| 4803 | On non-fatal errors, png_warning() is called
|
|---|
| 4804 | to print a warning message, and then control returns to the calling code.
|
|---|
| 4805 | By default png_error() and png_warning() print a message on stderr via
|
|---|
| 4806 | fprintf() unless the library is compiled with PNG_NO_CONSOLE_IO defined
|
|---|
| 4807 | (because you don't want the messages) or PNG_NO_STDIO defined (because
|
|---|
| 4808 | fprintf() isn't available). If you wish to change the behavior of the error
|
|---|
| 4809 | functions, you will need to set up your own message callbacks. These
|
|---|
| 4810 | functions are normally supplied at the time that the png_struct is created.
|
|---|
| 4811 | It is also possible to redirect errors and warnings to your own replacement
|
|---|
| 4812 | functions after png_create_*_struct() has been called by calling:
|
|---|
| 4813 |
|
|---|
| 4814 | png_set_error_fn(png_structp png_ptr,
|
|---|
| 4815 | png_voidp error_ptr, png_error_ptr error_fn,
|
|---|
| 4816 | png_error_ptr warning_fn);
|
|---|
| 4817 |
|
|---|
| 4818 | If NULL is supplied for either error_fn or warning_fn, then the libpng
|
|---|
| 4819 | default function will be used, calling fprintf() and/or longjmp() if a
|
|---|
| 4820 | problem is encountered. The replacement error functions should have
|
|---|
| 4821 | parameters as follows:
|
|---|
| 4822 |
|
|---|
| 4823 | void user_error_fn(png_structp png_ptr,
|
|---|
| 4824 | png_const_charp error_msg);
|
|---|
| 4825 |
|
|---|
| 4826 | void user_warning_fn(png_structp png_ptr,
|
|---|
| 4827 | png_const_charp warning_msg);
|
|---|
| 4828 |
|
|---|
| 4829 | Then, within your user_error_fn or user_warning_fn, you can retrieve
|
|---|
| 4830 | the error_ptr if you need it, by calling
|
|---|
| 4831 |
|
|---|
| 4832 | png_voidp error_ptr = png_get_error_ptr(png_ptr);
|
|---|
| 4833 |
|
|---|
| 4834 | The motivation behind using setjmp() and longjmp() is the C++ throw and
|
|---|
| 4835 | catch exception handling methods. This makes the code much easier to write,
|
|---|
| 4836 | as there is no need to check every return code of every function call.
|
|---|
| 4837 | However, there are some uncertainties about the status of local variables
|
|---|
| 4838 | after a longjmp, so the user may want to be careful about doing anything
|
|---|
| 4839 | after setjmp returns non-zero besides returning itself. Consult your
|
|---|
| 4840 | compiler documentation for more details. For an alternative approach, you
|
|---|
| 4841 | may wish to use the "cexcept" facility (see https://cexcept.sourceforge.io/),
|
|---|
| 4842 | which is illustrated in pngvalid.c and in contrib/visupng.
|
|---|
| 4843 |
|
|---|
| 4844 | Beginning in libpng-1.4.0, the png_set_benign_errors() API became available.
|
|---|
| 4845 | You can use this to handle certain errors (normally handled as errors)
|
|---|
| 4846 | as warnings.
|
|---|
| 4847 |
|
|---|
| 4848 | png_set_benign_errors (png_ptr, int allowed);
|
|---|
| 4849 |
|
|---|
| 4850 | allowed: 0: treat png_benign_error() as an error.
|
|---|
| 4851 | 1: treat png_benign_error() as a warning.
|
|---|
| 4852 |
|
|---|
| 4853 | As of libpng-1.6.0, the default condition is to treat benign errors as
|
|---|
| 4854 | warnings while reading and as errors while writing.
|
|---|
| 4855 |
|
|---|
| 4856 | .SS Custom chunks
|
|---|
| 4857 |
|
|---|
| 4858 | If you need to read or write custom chunks, you may need to get deeper
|
|---|
| 4859 | into the libpng code. The library now has mechanisms for storing
|
|---|
| 4860 | and writing chunks of unknown type; you can even declare callbacks
|
|---|
| 4861 | for custom chunks. However, this may not be good enough if the
|
|---|
| 4862 | library code itself needs to know about interactions between your
|
|---|
| 4863 | chunk and existing `intrinsic' chunks.
|
|---|
| 4864 |
|
|---|
| 4865 | If you need to write a new intrinsic chunk, first read the PNG
|
|---|
| 4866 | specification. Acquire a first level of understanding of how it works.
|
|---|
| 4867 | Pay particular attention to the sections that describe chunk names,
|
|---|
| 4868 | and look at how other chunks were designed, so you can do things
|
|---|
| 4869 | similarly. Second, check out the sections of libpng that read and
|
|---|
| 4870 | write chunks. Try to find a chunk that is similar to yours and use
|
|---|
| 4871 | it as a template. More details can be found in the comments inside
|
|---|
| 4872 | the code. It is best to handle private or unknown chunks in a generic method,
|
|---|
| 4873 | via callback functions, instead of by modifying libpng functions. This
|
|---|
| 4874 | is illustrated in pngtest.c, which uses a callback function to handle a
|
|---|
| 4875 | private "vpAg" chunk and the new "sTER" chunk, which are both unknown to
|
|---|
| 4876 | libpng.
|
|---|
| 4877 |
|
|---|
| 4878 | If you wish to write your own transformation for the data, look through
|
|---|
| 4879 | the part of the code that does the transformations, and check out some of
|
|---|
| 4880 | the simpler ones to get an idea of how they work. Try to find a similar
|
|---|
| 4881 | transformation to the one you want to add and copy off of it. More details
|
|---|
| 4882 | can be found in the comments inside the code itself.
|
|---|
| 4883 |
|
|---|
| 4884 | .SS Configuring for gui/windowing platforms:
|
|---|
| 4885 |
|
|---|
| 4886 | You will need to write new error and warning functions that use the GUI
|
|---|
| 4887 | interface, as described previously, and set them to be the error and
|
|---|
| 4888 | warning functions at the time that png_create_*_struct() is called,
|
|---|
| 4889 | in order to have them available during the structure initialization.
|
|---|
| 4890 | They can be changed later via png_set_error_fn(). On some compilers,
|
|---|
| 4891 | you may also have to change the memory allocators (png_malloc, etc.).
|
|---|
| 4892 |
|
|---|
| 4893 | .SS Configuring zlib:
|
|---|
| 4894 |
|
|---|
| 4895 | There are special functions to configure the compression. Perhaps the
|
|---|
| 4896 | most useful one changes the compression level, which currently uses
|
|---|
| 4897 | input compression values in the range 0 - 9. The library normally
|
|---|
| 4898 | uses the default compression level (Z_DEFAULT_COMPRESSION = 6). Tests
|
|---|
| 4899 | have shown that for a large majority of images, compression values in
|
|---|
| 4900 | the range 3-6 compress nearly as well as higher levels, and do so much
|
|---|
| 4901 | faster. For online applications it may be desirable to have maximum speed
|
|---|
| 4902 | (Z_BEST_SPEED = 1). With versions of zlib after v0.99, you can also
|
|---|
| 4903 | specify no compression (Z_NO_COMPRESSION = 0), but this would create
|
|---|
| 4904 | files larger than just storing the raw bitmap. You can specify the
|
|---|
| 4905 | compression level by calling:
|
|---|
| 4906 |
|
|---|
| 4907 | #include zlib.h
|
|---|
| 4908 | png_set_compression_level(png_ptr, level);
|
|---|
| 4909 |
|
|---|
| 4910 | Another useful one is to reduce the memory level used by the library.
|
|---|
| 4911 | The memory level defaults to 8, but it can be lowered if you are
|
|---|
| 4912 | short on memory (running DOS, for example, where you only have 640K).
|
|---|
| 4913 | Note that the memory level does have an effect on compression; among
|
|---|
| 4914 | other things, lower levels will result in sections of incompressible
|
|---|
| 4915 | data being emitted in smaller stored blocks, with a correspondingly
|
|---|
| 4916 | larger relative overhead of up to 15% in the worst case.
|
|---|
| 4917 |
|
|---|
| 4918 | #include zlib.h
|
|---|
| 4919 | png_set_compression_mem_level(png_ptr, level);
|
|---|
| 4920 |
|
|---|
| 4921 | The other functions are for configuring zlib. They are not recommended
|
|---|
| 4922 | for normal use and may result in writing an invalid PNG file. See
|
|---|
| 4923 | zlib.h for more information on what these mean.
|
|---|
| 4924 |
|
|---|
| 4925 | #include zlib.h
|
|---|
| 4926 | png_set_compression_strategy(png_ptr,
|
|---|
| 4927 | strategy);
|
|---|
| 4928 |
|
|---|
| 4929 | png_set_compression_window_bits(png_ptr,
|
|---|
| 4930 | window_bits);
|
|---|
| 4931 |
|
|---|
| 4932 | png_set_compression_method(png_ptr, method);
|
|---|
| 4933 |
|
|---|
| 4934 | This controls the size of the IDAT chunks (default 8192):
|
|---|
| 4935 |
|
|---|
| 4936 | png_set_compression_buffer_size(png_ptr, size);
|
|---|
| 4937 |
|
|---|
| 4938 | As of libpng version 1.5.4, additional APIs became
|
|---|
| 4939 | available to set these separately for non-IDAT
|
|---|
| 4940 | compressed chunks such as zTXt, iTXt, and iCCP:
|
|---|
| 4941 |
|
|---|
| 4942 | #include zlib.h
|
|---|
| 4943 | #if PNG_LIBPNG_VER >= 10504
|
|---|
| 4944 | png_set_text_compression_level(png_ptr, level);
|
|---|
| 4945 |
|
|---|
| 4946 | png_set_text_compression_mem_level(png_ptr, level);
|
|---|
| 4947 |
|
|---|
| 4948 | png_set_text_compression_strategy(png_ptr,
|
|---|
| 4949 | strategy);
|
|---|
| 4950 |
|
|---|
| 4951 | png_set_text_compression_window_bits(png_ptr,
|
|---|
| 4952 | window_bits);
|
|---|
| 4953 |
|
|---|
| 4954 | png_set_text_compression_method(png_ptr, method);
|
|---|
| 4955 | #endif
|
|---|
| 4956 |
|
|---|
| 4957 | .SS Controlling row filtering
|
|---|
| 4958 |
|
|---|
| 4959 | If you want to control whether libpng uses filtering or not, which
|
|---|
| 4960 | filters are used, and how it goes about picking row filters, you
|
|---|
| 4961 | can call one of these functions. The selection and configuration
|
|---|
| 4962 | of row filters can have a significant impact on the size and
|
|---|
| 4963 | encoding speed and a somewhat lesser impact on the decoding speed
|
|---|
| 4964 | of an image. Filtering is enabled by default for RGB and grayscale
|
|---|
| 4965 | images (with and without alpha), but not for paletted images nor
|
|---|
| 4966 | for any images with bit depths less than 8 bits/pixel.
|
|---|
| 4967 |
|
|---|
| 4968 | The 'method' parameter sets the main filtering method, which is
|
|---|
| 4969 | currently only '0' in the PNG 1.2 specification. The 'filters'
|
|---|
| 4970 | parameter sets which filter(s), if any, should be used for each
|
|---|
| 4971 | scanline. Possible values are PNG_ALL_FILTERS, PNG_NO_FILTERS,
|
|---|
| 4972 | or PNG_FAST_FILTERS to turn filtering on and off, or to turn on
|
|---|
| 4973 | just the fast-decoding subset of filters, respectively.
|
|---|
| 4974 |
|
|---|
| 4975 | Individual filter types are PNG_FILTER_NONE, PNG_FILTER_SUB,
|
|---|
| 4976 | PNG_FILTER_UP, PNG_FILTER_AVG, PNG_FILTER_PAETH, which can be bitwise
|
|---|
| 4977 | ORed together with '|' to specify one or more filters to use.
|
|---|
| 4978 | These filters are described in more detail in the PNG specification.
|
|---|
| 4979 | If you intend to change the filter type during the course of writing
|
|---|
| 4980 | the image, you should start with flags set for all of the filters
|
|---|
| 4981 | you intend to use so that libpng can initialize its internal
|
|---|
| 4982 | structures appropriately for all of the filter types. (Note that this
|
|---|
| 4983 | means the first row must always be adaptively filtered, because libpng
|
|---|
| 4984 | currently does not allocate the filter buffers until png_write_row()
|
|---|
| 4985 | is called for the first time.)
|
|---|
| 4986 |
|
|---|
| 4987 | filters = PNG_NO_FILTERS;
|
|---|
| 4988 | filters = PNG_ALL_FILTERS;
|
|---|
| 4989 | filters = PNG_FAST_FILTERS;
|
|---|
| 4990 |
|
|---|
| 4991 | or
|
|---|
| 4992 |
|
|---|
| 4993 | filters = PNG_FILTER_NONE | PNG_FILTER_SUB |
|
|---|
| 4994 | PNG_FILTER_UP | PNG_FILTER_AVG |
|
|---|
| 4995 | PNG_FILTER_PAETH;
|
|---|
| 4996 |
|
|---|
| 4997 | png_set_filter(png_ptr, PNG_FILTER_TYPE_BASE,
|
|---|
| 4998 | filters);
|
|---|
| 4999 |
|
|---|
| 5000 | The second parameter can also be
|
|---|
| 5001 | PNG_INTRAPIXEL_DIFFERENCING if you are
|
|---|
| 5002 | writing a PNG to be embedded in a MNG
|
|---|
| 5003 | datastream. This parameter must be the
|
|---|
| 5004 | same as the value of filter_method used
|
|---|
| 5005 | in png_set_IHDR().
|
|---|
| 5006 |
|
|---|
| 5007 | .SS Requesting debug printout
|
|---|
| 5008 |
|
|---|
| 5009 | The macro definition PNG_DEBUG can be used to request debugging
|
|---|
| 5010 | printout. Set it to an integer value in the range 0 to 3. Higher
|
|---|
| 5011 | numbers result in increasing amounts of debugging information. The
|
|---|
| 5012 | information is printed to the "stderr" file, unless another file
|
|---|
| 5013 | name is specified in the PNG_DEBUG_FILE macro definition.
|
|---|
| 5014 |
|
|---|
| 5015 | When PNG_DEBUG > 0, the following functions (macros) become available:
|
|---|
| 5016 |
|
|---|
| 5017 | png_debug(level, message)
|
|---|
| 5018 | png_debug1(level, message, p1)
|
|---|
| 5019 | png_debug2(level, message, p1, p2)
|
|---|
| 5020 |
|
|---|
| 5021 | in which "level" is compared to PNG_DEBUG to decide whether to print
|
|---|
| 5022 | the message, "message" is the formatted string to be printed,
|
|---|
| 5023 | and p1 and p2 are parameters that are to be embedded in the string
|
|---|
| 5024 | according to printf-style formatting directives. For example,
|
|---|
| 5025 |
|
|---|
| 5026 | png_debug1(2, "foo=%d", foo);
|
|---|
| 5027 |
|
|---|
| 5028 | is expanded to
|
|---|
| 5029 |
|
|---|
| 5030 | if (PNG_DEBUG > 2)
|
|---|
| 5031 | fprintf(PNG_DEBUG_FILE, "foo=%d\en", foo);
|
|---|
| 5032 |
|
|---|
| 5033 | When PNG_DEBUG is defined but is zero, the macros aren't defined, but you
|
|---|
| 5034 | can still use PNG_DEBUG to control your own debugging:
|
|---|
| 5035 |
|
|---|
| 5036 | #ifdef PNG_DEBUG
|
|---|
| 5037 | fprintf(stderr, ...
|
|---|
| 5038 | #endif
|
|---|
| 5039 |
|
|---|
| 5040 | When PNG_DEBUG = 1, the macros are defined, but only png_debug statements
|
|---|
| 5041 | having level = 0 will be printed. There aren't any such statements in
|
|---|
| 5042 | this version of libpng, but if you insert some they will be printed.
|
|---|
| 5043 |
|
|---|
| 5044 | .SH VII. MNG support
|
|---|
| 5045 |
|
|---|
| 5046 | The MNG specification (available at http://www.libpng.org/pub/mng) allows
|
|---|
| 5047 | certain extensions to PNG for PNG images that are embedded in MNG datastreams.
|
|---|
| 5048 | Libpng can support some of these extensions. To enable them, use the
|
|---|
| 5049 | png_permit_mng_features() function:
|
|---|
| 5050 |
|
|---|
| 5051 | feature_set = png_permit_mng_features(png_ptr, mask)
|
|---|
| 5052 |
|
|---|
| 5053 | mask is a png_uint_32 containing the bitwise OR of the
|
|---|
| 5054 | features you want to enable. These include
|
|---|
| 5055 | PNG_FLAG_MNG_EMPTY_PLTE
|
|---|
| 5056 | PNG_FLAG_MNG_FILTER_64
|
|---|
| 5057 | PNG_ALL_MNG_FEATURES
|
|---|
| 5058 |
|
|---|
| 5059 | feature_set is a png_uint_32 that is the bitwise AND of
|
|---|
| 5060 | your mask with the set of MNG features that is
|
|---|
| 5061 | supported by the version of libpng that you are using.
|
|---|
| 5062 |
|
|---|
| 5063 | It is an error to use this function when reading or writing a standalone
|
|---|
| 5064 | PNG file with the PNG 8-byte signature. The PNG datastream must be wrapped
|
|---|
| 5065 | in a MNG datastream. As a minimum, it must have the MNG 8-byte signature
|
|---|
| 5066 | and the MHDR and MEND chunks. Libpng does not provide support for these
|
|---|
| 5067 | or any other MNG chunks; your application must provide its own support for
|
|---|
| 5068 | them. You may wish to consider using libmng (available at
|
|---|
| 5069 | https://www.libmng.com/) instead.
|
|---|
| 5070 |
|
|---|
| 5071 | .SH VIII. Changes to Libpng from version 0.88
|
|---|
| 5072 |
|
|---|
| 5073 | It should be noted that versions of libpng later than 0.96 are not
|
|---|
| 5074 | distributed by the original libpng author, Guy Schalnat, nor by
|
|---|
| 5075 | Andreas Dilger, who had taken over from Guy during 1996 and 1997, and
|
|---|
| 5076 | distributed versions 0.89 through 0.96, but rather by another member
|
|---|
| 5077 | of the original PNG Group, Glenn Randers-Pehrson. Guy and Andreas are
|
|---|
| 5078 | still alive and well, but they have moved on to other things.
|
|---|
| 5079 |
|
|---|
| 5080 | The old libpng functions png_read_init(), png_write_init(),
|
|---|
| 5081 | png_info_init(), png_read_destroy(), and png_write_destroy() have been
|
|---|
| 5082 | moved to PNG_INTERNAL in version 0.95 to discourage their use. These
|
|---|
| 5083 | functions will be removed from libpng version 1.4.0.
|
|---|
| 5084 |
|
|---|
| 5085 | The preferred method of creating and initializing the libpng structures is
|
|---|
| 5086 | via the png_create_read_struct(), png_create_write_struct(), and
|
|---|
| 5087 | png_create_info_struct() because they isolate the size of the structures
|
|---|
| 5088 | from the application, allow version error checking, and also allow the
|
|---|
| 5089 | use of custom error handling routines during the initialization, which
|
|---|
| 5090 | the old functions do not. The functions png_read_destroy() and
|
|---|
| 5091 | png_write_destroy() do not actually free the memory that libpng
|
|---|
| 5092 | allocated for these structs, but just reset the data structures, so they
|
|---|
| 5093 | can be used instead of png_destroy_read_struct() and
|
|---|
| 5094 | png_destroy_write_struct() if you feel there is too much system overhead
|
|---|
| 5095 | allocating and freeing the png_struct for each image read.
|
|---|
| 5096 |
|
|---|
| 5097 | Setting the error callbacks via png_set_message_fn() before
|
|---|
| 5098 | png_read_init() as was suggested in libpng-0.88 is no longer supported
|
|---|
| 5099 | because this caused applications that do not use custom error functions
|
|---|
| 5100 | to fail if the png_ptr was not initialized to zero. It is still possible
|
|---|
| 5101 | to set the error callbacks AFTER png_read_init(), or to change them with
|
|---|
| 5102 | png_set_error_fn(), which is essentially the same function, but with a new
|
|---|
| 5103 | name to force compilation errors with applications that try to use the old
|
|---|
| 5104 | method.
|
|---|
| 5105 |
|
|---|
| 5106 | Support for the sCAL, iCCP, iTXt, and sPLT chunks was added at libpng-1.0.6;
|
|---|
| 5107 | however, iTXt support was not enabled by default.
|
|---|
| 5108 |
|
|---|
| 5109 | Starting with version 1.0.7, you can find out which version of the library
|
|---|
| 5110 | you are using at run-time:
|
|---|
| 5111 |
|
|---|
| 5112 | png_uint_32 libpng_vn = png_access_version_number();
|
|---|
| 5113 |
|
|---|
| 5114 | The number libpng_vn is constructed from the major version, minor
|
|---|
| 5115 | version with leading zero, and release number with leading zero,
|
|---|
| 5116 | (e.g., libpng_vn for version 1.0.7 is 10007).
|
|---|
| 5117 |
|
|---|
| 5118 | Note that this function does not take a png_ptr, so you can call it
|
|---|
| 5119 | before you've created one.
|
|---|
| 5120 |
|
|---|
| 5121 | You can also check which version of png.h you used when compiling your
|
|---|
| 5122 | application:
|
|---|
| 5123 |
|
|---|
| 5124 | png_uint_32 application_vn = PNG_LIBPNG_VER;
|
|---|
| 5125 |
|
|---|
| 5126 | .SH IX. Changes to Libpng from version 1.0.x to 1.2.x
|
|---|
| 5127 |
|
|---|
| 5128 | Support for user memory management was enabled by default. To
|
|---|
| 5129 | accomplish this, the functions png_create_read_struct_2(),
|
|---|
| 5130 | png_create_write_struct_2(), png_set_mem_fn(), png_get_mem_ptr(),
|
|---|
| 5131 | png_malloc_default(), and png_free_default() were added.
|
|---|
| 5132 |
|
|---|
| 5133 | Support for the iTXt chunk has been enabled by default as of
|
|---|
| 5134 | version 1.2.41.
|
|---|
| 5135 |
|
|---|
| 5136 | Support for certain MNG features was enabled.
|
|---|
| 5137 |
|
|---|
| 5138 | Support for numbered error messages was added. However, we never got
|
|---|
| 5139 | around to actually numbering the error messages. The function
|
|---|
| 5140 | png_set_strip_error_numbers() was added (Note: the prototype for this
|
|---|
| 5141 | function was inadvertently removed from png.h in PNG_NO_ASSEMBLER_CODE
|
|---|
| 5142 | builds of libpng-1.2.15. It was restored in libpng-1.2.36).
|
|---|
| 5143 |
|
|---|
| 5144 | The png_malloc_warn() function was added at libpng-1.2.3. This issues
|
|---|
| 5145 | a png_warning and returns NULL instead of aborting when it fails to
|
|---|
| 5146 | acquire the requested memory allocation.
|
|---|
| 5147 |
|
|---|
| 5148 | Support for setting user limits on image width and height was enabled
|
|---|
| 5149 | by default. The functions png_set_user_limits(), png_get_user_width_max(),
|
|---|
| 5150 | and png_get_user_height_max() were added at libpng-1.2.6.
|
|---|
| 5151 |
|
|---|
| 5152 | The png_set_add_alpha() function was added at libpng-1.2.7.
|
|---|
| 5153 |
|
|---|
| 5154 | The function png_set_expand_gray_1_2_4_to_8() was added at libpng-1.2.9.
|
|---|
| 5155 | Unlike png_set_gray_1_2_4_to_8(), the new function does not expand the
|
|---|
| 5156 | tRNS chunk to alpha. The png_set_gray_1_2_4_to_8() function is
|
|---|
| 5157 | deprecated.
|
|---|
| 5158 |
|
|---|
| 5159 | A number of macro definitions in support of runtime selection of
|
|---|
| 5160 | assembler code features (especially Intel MMX code support) were
|
|---|
| 5161 | added at libpng-1.2.0:
|
|---|
| 5162 |
|
|---|
| 5163 | PNG_ASM_FLAG_MMX_SUPPORT_COMPILED
|
|---|
| 5164 | PNG_ASM_FLAG_MMX_SUPPORT_IN_CPU
|
|---|
| 5165 | PNG_ASM_FLAG_MMX_READ_COMBINE_ROW
|
|---|
| 5166 | PNG_ASM_FLAG_MMX_READ_INTERLACE
|
|---|
| 5167 | PNG_ASM_FLAG_MMX_READ_FILTER_SUB
|
|---|
| 5168 | PNG_ASM_FLAG_MMX_READ_FILTER_UP
|
|---|
| 5169 | PNG_ASM_FLAG_MMX_READ_FILTER_AVG
|
|---|
| 5170 | PNG_ASM_FLAG_MMX_READ_FILTER_PAETH
|
|---|
| 5171 | PNG_ASM_FLAGS_INITIALIZED
|
|---|
| 5172 | PNG_MMX_READ_FLAGS
|
|---|
| 5173 | PNG_MMX_FLAGS
|
|---|
| 5174 | PNG_MMX_WRITE_FLAGS
|
|---|
| 5175 | PNG_MMX_FLAGS
|
|---|
| 5176 |
|
|---|
| 5177 | We added the following functions in support of runtime
|
|---|
| 5178 | selection of assembler code features:
|
|---|
| 5179 |
|
|---|
| 5180 | png_get_mmx_flagmask()
|
|---|
| 5181 | png_set_mmx_thresholds()
|
|---|
| 5182 | png_get_asm_flags()
|
|---|
| 5183 | png_get_mmx_bitdepth_threshold()
|
|---|
| 5184 | png_get_mmx_rowbytes_threshold()
|
|---|
| 5185 | png_set_asm_flags()
|
|---|
| 5186 |
|
|---|
| 5187 | We replaced all of these functions with simple stubs in libpng-1.2.20,
|
|---|
| 5188 | when the Intel assembler code was removed due to a licensing issue.
|
|---|
| 5189 |
|
|---|
| 5190 | These macros are deprecated:
|
|---|
| 5191 |
|
|---|
| 5192 | PNG_READ_TRANSFORMS_NOT_SUPPORTED
|
|---|
| 5193 | PNG_PROGRESSIVE_READ_NOT_SUPPORTED
|
|---|
| 5194 | PNG_NO_SEQUENTIAL_READ_SUPPORTED
|
|---|
| 5195 | PNG_WRITE_TRANSFORMS_NOT_SUPPORTED
|
|---|
| 5196 | PNG_READ_ANCILLARY_CHUNKS_NOT_SUPPORTED
|
|---|
| 5197 | PNG_WRITE_ANCILLARY_CHUNKS_NOT_SUPPORTED
|
|---|
| 5198 |
|
|---|
| 5199 | They have been replaced, respectively, by:
|
|---|
| 5200 |
|
|---|
| 5201 | PNG_NO_READ_TRANSFORMS
|
|---|
| 5202 | PNG_NO_PROGRESSIVE_READ
|
|---|
| 5203 | PNG_NO_SEQUENTIAL_READ
|
|---|
| 5204 | PNG_NO_WRITE_TRANSFORMS
|
|---|
| 5205 | PNG_NO_READ_ANCILLARY_CHUNKS
|
|---|
| 5206 | PNG_NO_WRITE_ANCILLARY_CHUNKS
|
|---|
| 5207 |
|
|---|
| 5208 | PNG_MAX_UINT was replaced with PNG_UINT_31_MAX. It has been
|
|---|
| 5209 | deprecated since libpng-1.0.16 and libpng-1.2.6.
|
|---|
| 5210 |
|
|---|
| 5211 | The function
|
|---|
| 5212 | png_check_sig(sig, num)
|
|---|
| 5213 | was replaced with
|
|---|
| 5214 | !png_sig_cmp(sig, 0, num)
|
|---|
| 5215 | It has been deprecated since libpng-0.90.
|
|---|
| 5216 |
|
|---|
| 5217 | The function
|
|---|
| 5218 | png_set_gray_1_2_4_to_8()
|
|---|
| 5219 | which also expands tRNS to alpha was replaced with
|
|---|
| 5220 | png_set_expand_gray_1_2_4_to_8()
|
|---|
| 5221 | which does not. It has been deprecated since libpng-1.0.18 and 1.2.9.
|
|---|
| 5222 |
|
|---|
| 5223 | .SH X. Changes to Libpng from version 1.0.x/1.2.x to 1.4.x
|
|---|
| 5224 |
|
|---|
| 5225 | Private libpng prototypes and macro definitions were moved from
|
|---|
| 5226 | png.h and pngconf.h into a new pngpriv.h header file.
|
|---|
| 5227 |
|
|---|
| 5228 | Functions png_set_benign_errors(), png_benign_error(), and
|
|---|
| 5229 | png_chunk_benign_error() were added.
|
|---|
| 5230 |
|
|---|
| 5231 | Support for setting the maximum amount of memory that the application
|
|---|
| 5232 | will allocate for reading chunks was added, as a security measure.
|
|---|
| 5233 | The functions png_set_chunk_cache_max() and png_get_chunk_cache_max()
|
|---|
| 5234 | were added to the library.
|
|---|
| 5235 |
|
|---|
| 5236 | We implemented support for I/O states by adding png_ptr member io_state
|
|---|
| 5237 | and functions png_get_io_chunk_name() and png_get_io_state() in pngget.c
|
|---|
| 5238 |
|
|---|
| 5239 | We added PNG_TRANSFORM_GRAY_TO_RGB to the available high-level
|
|---|
| 5240 | input transforms.
|
|---|
| 5241 |
|
|---|
| 5242 | Checking for and reporting of errors in the IHDR chunk is more thorough.
|
|---|
| 5243 |
|
|---|
| 5244 | Support for global arrays was removed, to improve thread safety.
|
|---|
| 5245 |
|
|---|
| 5246 | Some obsolete/deprecated macros and functions have been removed.
|
|---|
| 5247 |
|
|---|
| 5248 | Typecasted NULL definitions such as
|
|---|
| 5249 | #define png_voidp_NULL (png_voidp)NULL
|
|---|
| 5250 | were eliminated. If you used these in your application, just use
|
|---|
| 5251 | NULL instead.
|
|---|
| 5252 |
|
|---|
| 5253 | The png_struct and info_struct members "trans" and "trans_values" were
|
|---|
| 5254 | changed to "trans_alpha" and "trans_color", respectively.
|
|---|
| 5255 |
|
|---|
| 5256 | The obsolete, unused pnggccrd.c and pngvcrd.c files and related makefiles
|
|---|
| 5257 | were removed.
|
|---|
| 5258 |
|
|---|
| 5259 | The PNG_1_0_X and PNG_1_2_X macros were eliminated.
|
|---|
| 5260 |
|
|---|
| 5261 | The PNG_LEGACY_SUPPORTED macro was eliminated.
|
|---|
| 5262 |
|
|---|
| 5263 | Many WIN32_WCE #ifdefs were removed.
|
|---|
| 5264 |
|
|---|
| 5265 | The functions png_read_init(info_ptr), png_write_init(info_ptr),
|
|---|
| 5266 | png_info_init(info_ptr), png_read_destroy(), and png_write_destroy()
|
|---|
| 5267 | have been removed. They have been deprecated since libpng-0.95.
|
|---|
| 5268 |
|
|---|
| 5269 | The png_permit_empty_plte() was removed. It has been deprecated
|
|---|
| 5270 | since libpng-1.0.9. Use png_permit_mng_features() instead.
|
|---|
| 5271 |
|
|---|
| 5272 | We removed the obsolete stub functions png_get_mmx_flagmask(),
|
|---|
| 5273 | png_set_mmx_thresholds(), png_get_asm_flags(),
|
|---|
| 5274 | png_get_mmx_bitdepth_threshold(), png_get_mmx_rowbytes_threshold(),
|
|---|
| 5275 | png_set_asm_flags(), and png_mmx_supported()
|
|---|
| 5276 |
|
|---|
| 5277 | We removed the obsolete png_check_sig(), png_memcpy_check(), and
|
|---|
| 5278 | png_memset_check() functions. Instead use !png_sig_cmp(), memcpy(),
|
|---|
| 5279 | and memset(), respectively.
|
|---|
| 5280 |
|
|---|
| 5281 | The function png_set_gray_1_2_4_to_8() was removed. It has been
|
|---|
| 5282 | deprecated since libpng-1.0.18 and 1.2.9, when it was replaced with
|
|---|
| 5283 | png_set_expand_gray_1_2_4_to_8() because the former function also
|
|---|
| 5284 | expanded any tRNS chunk to an alpha channel.
|
|---|
| 5285 |
|
|---|
| 5286 | Macros for png_get_uint_16, png_get_uint_32, and png_get_int_32
|
|---|
| 5287 | were added and are used by default instead of the corresponding
|
|---|
| 5288 | functions. Unfortunately,
|
|---|
| 5289 | from libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the
|
|---|
| 5290 | function) incorrectly returned a value of type png_uint_32.
|
|---|
| 5291 |
|
|---|
| 5292 | We changed the prototype for png_malloc() from
|
|---|
| 5293 | png_malloc(png_structp png_ptr, png_uint_32 size)
|
|---|
| 5294 | to
|
|---|
| 5295 | png_malloc(png_structp png_ptr, png_alloc_size_t size)
|
|---|
| 5296 |
|
|---|
| 5297 | This also applies to the prototype for the user replacement malloc_fn().
|
|---|
| 5298 |
|
|---|
| 5299 | The png_calloc() function was added and is used in place of
|
|---|
| 5300 | of "png_malloc(); memset();" except in the case in png_read_png()
|
|---|
| 5301 | where the array consists of pointers; in this case a "for" loop is used
|
|---|
| 5302 | after the png_malloc() to set the pointers to NULL, to give robust.
|
|---|
| 5303 | behavior in case the application runs out of memory part-way through
|
|---|
| 5304 | the process.
|
|---|
| 5305 |
|
|---|
| 5306 | We changed the prototypes of png_get_compression_buffer_size() and
|
|---|
| 5307 | png_set_compression_buffer_size() to work with size_t instead of
|
|---|
| 5308 | png_uint_32.
|
|---|
| 5309 |
|
|---|
| 5310 | Support for numbered error messages was removed by default, since we
|
|---|
| 5311 | never got around to actually numbering the error messages. The function
|
|---|
| 5312 | png_set_strip_error_numbers() was removed from the library by default.
|
|---|
| 5313 |
|
|---|
| 5314 | The png_zalloc() and png_zfree() functions are no longer exported.
|
|---|
| 5315 | The png_zalloc() function no longer zeroes out the memory that it
|
|---|
| 5316 | allocates. Applications that called png_zalloc(png_ptr, number, size)
|
|---|
| 5317 | can call png_calloc(png_ptr, number*size) instead, and can call
|
|---|
| 5318 | png_free() instead of png_zfree().
|
|---|
| 5319 |
|
|---|
| 5320 | Support for dithering was disabled by default in libpng-1.4.0, because
|
|---|
| 5321 | it has not been well tested and doesn't actually "dither".
|
|---|
| 5322 | The code was not
|
|---|
| 5323 | removed, however, and could be enabled by building libpng with
|
|---|
| 5324 | PNG_READ_DITHER_SUPPORTED defined. In libpng-1.4.2, this support
|
|---|
| 5325 | was re-enabled, but the function was renamed png_set_quantize() to
|
|---|
| 5326 | reflect more accurately what it actually does. At the same time,
|
|---|
| 5327 | the PNG_DITHER_[RED,GREEN_BLUE]_BITS macros were also renamed to
|
|---|
| 5328 | PNG_QUANTIZE_[RED,GREEN,BLUE]_BITS, and PNG_READ_DITHER_SUPPORTED
|
|---|
| 5329 | was renamed to PNG_READ_QUANTIZE_SUPPORTED.
|
|---|
| 5330 |
|
|---|
| 5331 | We removed the trailing '.' from the warning and error messages.
|
|---|
| 5332 |
|
|---|
| 5333 | .SH XI. Changes to Libpng from version 1.4.x to 1.5.x
|
|---|
| 5334 |
|
|---|
| 5335 | From libpng-1.4.0 until 1.4.4, the png_get_uint_16 macro (but not the
|
|---|
| 5336 | function) incorrectly returned a value of type png_uint_32.
|
|---|
| 5337 | The incorrect macro was removed from libpng-1.4.5.
|
|---|
| 5338 |
|
|---|
| 5339 | Checking for invalid palette index on write was added at libpng
|
|---|
| 5340 | 1.5.10. If a pixel contains an invalid (out-of-range) index libpng issues
|
|---|
| 5341 | a benign error. This is enabled by default because this condition is an
|
|---|
| 5342 | error according to the PNG specification, Clause 11.3.2, but the error can
|
|---|
| 5343 | be ignored in each png_ptr with
|
|---|
| 5344 |
|
|---|
| 5345 | png_set_check_for_invalid_index(png_ptr, allowed);
|
|---|
| 5346 |
|
|---|
| 5347 | allowed - one of
|
|---|
| 5348 | 0: disable benign error (accept the
|
|---|
| 5349 | invalid data without warning).
|
|---|
| 5350 | 1: enable benign error (treat the
|
|---|
| 5351 | invalid data as an error or a
|
|---|
| 5352 | warning).
|
|---|
| 5353 |
|
|---|
| 5354 | If the error is ignored, or if png_benign_error() treats it as a warning,
|
|---|
| 5355 | any invalid pixels are decoded as opaque black by the decoder and written
|
|---|
| 5356 | as-is by the encoder.
|
|---|
| 5357 |
|
|---|
| 5358 | Retrieving the maximum palette index found was added at libpng-1.5.15.
|
|---|
| 5359 | This statement must appear after png_read_png() or png_read_image() while
|
|---|
| 5360 | reading, and after png_write_png() or png_write_image() while writing.
|
|---|
| 5361 |
|
|---|
| 5362 | int max_palette = png_get_palette_max(png_ptr, info_ptr);
|
|---|
| 5363 |
|
|---|
| 5364 | This will return the maximum palette index found in the image, or "\-1" if
|
|---|
| 5365 | the palette was not checked, or "0" if no palette was found. Note that this
|
|---|
| 5366 | does not account for any palette index used by ancillary chunks such as the
|
|---|
| 5367 | bKGD chunk; you must check those separately to determine the maximum
|
|---|
| 5368 | palette index actually used.
|
|---|
| 5369 |
|
|---|
| 5370 | There are no substantial API changes between the non-deprecated parts of
|
|---|
| 5371 | the 1.4.5 API and the 1.5.0 API; however, the ability to directly access
|
|---|
| 5372 | members of the main libpng control structures, png_struct and png_info,
|
|---|
| 5373 | deprecated in earlier versions of libpng, has been completely removed from
|
|---|
| 5374 | libpng 1.5, and new private "pngstruct.h", "pnginfo.h", and "pngdebug.h"
|
|---|
| 5375 | header files were created.
|
|---|
| 5376 |
|
|---|
| 5377 | We no longer include zlib.h in png.h. The include statement has been moved
|
|---|
| 5378 | to pngstruct.h, where it is not accessible by applications. Applications that
|
|---|
| 5379 | need access to information in zlib.h will need to add the '#include "zlib.h"'
|
|---|
| 5380 | directive. It does not matter whether this is placed prior to or after
|
|---|
| 5381 | the '"#include png.h"' directive.
|
|---|
| 5382 |
|
|---|
| 5383 | The png_sprintf(), png_strcpy(), and png_strncpy() macros are no longer used
|
|---|
| 5384 | and were removed.
|
|---|
| 5385 |
|
|---|
| 5386 | We moved the png_strlen(), png_memcpy(), png_memset(), and png_memcmp()
|
|---|
| 5387 | macros into a private header file (pngpriv.h) that is not accessible to
|
|---|
| 5388 | applications.
|
|---|
| 5389 |
|
|---|
| 5390 | In png_get_iCCP, the type of "profile" was changed from png_charpp
|
|---|
| 5391 | to png_bytepp, and in png_set_iCCP, from png_charp to png_const_bytep.
|
|---|
| 5392 |
|
|---|
| 5393 | There are changes of form in png.h, including new and changed macros to
|
|---|
| 5394 | declare parts of the API. Some API functions with arguments that are
|
|---|
| 5395 | pointers to data not modified within the function have been corrected to
|
|---|
| 5396 | declare these arguments with const.
|
|---|
| 5397 |
|
|---|
| 5398 | Much of the internal use of C macros to control the library build has also
|
|---|
| 5399 | changed and some of this is visible in the exported header files, in
|
|---|
| 5400 | particular the use of macros to control data and API elements visible
|
|---|
| 5401 | during application compilation may require significant revision to
|
|---|
| 5402 | application code. (It is extremely rare for an application to do this.)
|
|---|
| 5403 |
|
|---|
| 5404 | Any program that compiled against libpng 1.4 and did not use deprecated
|
|---|
| 5405 | features or access internal library structures should compile and work
|
|---|
| 5406 | against libpng 1.5, except for the change in the prototype for
|
|---|
| 5407 | png_get_iCCP() and png_set_iCCP() API functions mentioned above.
|
|---|
| 5408 |
|
|---|
| 5409 | libpng 1.5.0 adds PNG_ PASS macros to help in the reading and writing of
|
|---|
| 5410 | interlaced images. The macros return the number of rows and columns in
|
|---|
| 5411 | each pass and information that can be used to de-interlace and (if
|
|---|
| 5412 | absolutely necessary) interlace an image.
|
|---|
| 5413 |
|
|---|
| 5414 | libpng 1.5.0 adds an API png_longjmp(png_ptr, value). This API calls
|
|---|
| 5415 | the application-provided png_longjmp_ptr on the internal, but application
|
|---|
| 5416 | initialized, longjmp buffer. It is provided as a convenience to avoid
|
|---|
| 5417 | the need to use the png_jmpbuf macro, which had the unnecessary side
|
|---|
| 5418 | effect of resetting the internal png_longjmp_ptr value.
|
|---|
| 5419 |
|
|---|
| 5420 | libpng 1.5.0 includes a complete fixed point API. By default this is
|
|---|
| 5421 | present along with the corresponding floating point API. In general the
|
|---|
| 5422 | fixed point API is faster and smaller than the floating point one because
|
|---|
| 5423 | the PNG file format used fixed point, not floating point. This applies
|
|---|
| 5424 | even if the library uses floating point in internal calculations. A new
|
|---|
| 5425 | macro, PNG_FLOATING_ARITHMETIC_SUPPORTED, reveals whether the library
|
|---|
| 5426 | uses floating point arithmetic (the default) or fixed point arithmetic
|
|---|
| 5427 | internally for performance critical calculations such as gamma correction.
|
|---|
| 5428 | In some cases, the gamma calculations may produce slightly different
|
|---|
| 5429 | results. This has changed the results in png_rgb_to_gray and in alpha
|
|---|
| 5430 | composition (png_set_background for example). This applies even if the
|
|---|
| 5431 | original image was already linear (gamma == 1.0) and, therefore, it is
|
|---|
| 5432 | not necessary to linearize the image. This is because libpng has *not*
|
|---|
| 5433 | been changed to optimize that case correctly, yet.
|
|---|
| 5434 |
|
|---|
| 5435 | Fixed point support for the sCAL chunk comes with an important caveat;
|
|---|
| 5436 | the sCAL specification uses a decimal encoding of floating point values
|
|---|
| 5437 | and the accuracy of PNG fixed point values is insufficient for
|
|---|
| 5438 | representation of these values. Consequently a "string" API
|
|---|
| 5439 | (png_get_sCAL_s and png_set_sCAL_s) is the only reliable way of reading
|
|---|
| 5440 | arbitrary sCAL chunks in the absence of either the floating point API or
|
|---|
| 5441 | internal floating point calculations. Starting with libpng-1.5.0, both
|
|---|
| 5442 | of these functions are present when PNG_sCAL_SUPPORTED is defined. Prior
|
|---|
| 5443 | to libpng-1.5.0, their presence also depended upon PNG_FIXED_POINT_SUPPORTED
|
|---|
| 5444 | being defined and PNG_FLOATING_POINT_SUPPORTED not being defined.
|
|---|
| 5445 |
|
|---|
| 5446 | Applications no longer need to include the optional distribution header
|
|---|
| 5447 | file pngusr.h or define the corresponding macros during application
|
|---|
| 5448 | build in order to see the correct variant of the libpng API. From 1.5.0
|
|---|
| 5449 | application code can check for the corresponding _SUPPORTED macro:
|
|---|
| 5450 |
|
|---|
| 5451 | #ifdef PNG_INCH_CONVERSIONS_SUPPORTED
|
|---|
| 5452 | /* code that uses the inch conversion APIs. */
|
|---|
| 5453 | #endif
|
|---|
| 5454 |
|
|---|
| 5455 | This macro will only be defined if the inch conversion functions have been
|
|---|
| 5456 | compiled into libpng. The full set of macros, and whether or not support
|
|---|
| 5457 | has been compiled in, are available in the header file pnglibconf.h.
|
|---|
| 5458 | This header file is specific to the libpng build. Notice that prior to
|
|---|
| 5459 | 1.5.0 the _SUPPORTED macros would always have the default definition unless
|
|---|
| 5460 | reset by pngusr.h or by explicit settings on the compiler command line.
|
|---|
| 5461 | These settings may produce compiler warnings or errors in 1.5.0 because
|
|---|
| 5462 | of macro redefinition.
|
|---|
| 5463 |
|
|---|
| 5464 | Applications can now choose whether to use these macros or to call the
|
|---|
| 5465 | corresponding function by defining PNG_USE_READ_MACROS or
|
|---|
| 5466 | PNG_NO_USE_READ_MACROS before including png.h. Notice that this is
|
|---|
| 5467 | only supported from 1.5.0; defining PNG_NO_USE_READ_MACROS prior to 1.5.0
|
|---|
| 5468 | will lead to a link failure.
|
|---|
| 5469 |
|
|---|
| 5470 | Prior to libpng-1.5.4, the zlib compressor used the same set of parameters
|
|---|
| 5471 | when compressing the IDAT data and textual data such as zTXt and iCCP.
|
|---|
| 5472 | In libpng-1.5.4 we reinitialized the zlib stream for each type of data.
|
|---|
| 5473 | We added five png_set_text_*() functions for setting the parameters to
|
|---|
| 5474 | use with textual data.
|
|---|
| 5475 |
|
|---|
| 5476 | Prior to libpng-1.5.4, the PNG_READ_16_TO_8_ACCURATE_SCALE_SUPPORTED
|
|---|
| 5477 | option was off by default, and slightly inaccurate scaling occurred.
|
|---|
| 5478 | This option can no longer be turned off, and the choice of accurate
|
|---|
| 5479 | or inaccurate 16-to-8 scaling is by using the new png_set_scale_16_to_8()
|
|---|
| 5480 | API for accurate scaling or the old png_set_strip_16_to_8() API for simple
|
|---|
| 5481 | chopping. In libpng-1.5.4, the PNG_READ_16_TO_8_ACCURATE_SCALE_SUPPORTED
|
|---|
| 5482 | macro became PNG_READ_SCALE_16_TO_8_SUPPORTED, and the PNG_READ_16_TO_8
|
|---|
| 5483 | macro became PNG_READ_STRIP_16_TO_8_SUPPORTED, to enable the two
|
|---|
| 5484 | png_set_*_16_to_8() functions separately.
|
|---|
| 5485 |
|
|---|
| 5486 | Prior to libpng-1.5.4, the png_set_user_limits() function could only be
|
|---|
| 5487 | used to reduce the width and height limits from the value of
|
|---|
| 5488 | PNG_USER_WIDTH_MAX and PNG_USER_HEIGHT_MAX, although this document said
|
|---|
| 5489 | that it could be used to override them. Now this function will reduce or
|
|---|
| 5490 | increase the limits.
|
|---|
| 5491 |
|
|---|
| 5492 | Starting in libpng-1.5.22, default user limits were established. These
|
|---|
| 5493 | can be overridden by application calls to png_set_user_limits(),
|
|---|
| 5494 | png_set_user_chunk_cache_max(), and/or png_set_user_malloc_max().
|
|---|
| 5495 | The limits are now
|
|---|
| 5496 | max possible default
|
|---|
| 5497 | png_user_width_max 0x7fffffff 1,000,000
|
|---|
| 5498 | png_user_height_max 0x7fffffff 1,000,000
|
|---|
| 5499 | png_user_chunk_cache_max 0 (unlimited) 1000
|
|---|
| 5500 | png_user_chunk_malloc_max 0 (unlimited) 8,000,000
|
|---|
| 5501 |
|
|---|
| 5502 | The png_set_option() function (and the "options" member of the png struct) was
|
|---|
| 5503 | added to libpng-1.5.15, with option PNG_ARM_NEON.
|
|---|
| 5504 |
|
|---|
| 5505 | The library now supports a complete fixed point implementation and can
|
|---|
| 5506 | thus be used on systems that have no floating point support or very
|
|---|
| 5507 | limited or slow support. Previously gamma correction, an essential part
|
|---|
| 5508 | of complete PNG support, required reasonably fast floating point.
|
|---|
| 5509 |
|
|---|
| 5510 | As part of this the choice of internal implementation has been made
|
|---|
| 5511 | independent of the choice of fixed versus floating point APIs and all the
|
|---|
| 5512 | missing fixed point APIs have been implemented.
|
|---|
| 5513 |
|
|---|
| 5514 | The exact mechanism used to control attributes of API functions has
|
|---|
| 5515 | changed, as described in the INSTALL file.
|
|---|
| 5516 |
|
|---|
| 5517 | A new test program, pngvalid, is provided in addition to pngtest.
|
|---|
| 5518 | pngvalid validates the arithmetic accuracy of the gamma correction
|
|---|
| 5519 | calculations and includes a number of validations of the file format.
|
|---|
| 5520 | A subset of the full range of tests is run when "make check" is done
|
|---|
| 5521 | (in the 'configure' build.) pngvalid also allows total allocated memory
|
|---|
| 5522 | usage to be evaluated and performs additional memory overwrite validation.
|
|---|
| 5523 |
|
|---|
| 5524 | Many changes to individual feature macros have been made. The following
|
|---|
| 5525 | are the changes most likely to be noticed by library builders who
|
|---|
| 5526 | configure libpng:
|
|---|
| 5527 |
|
|---|
| 5528 | 1) All feature macros now have consistent naming:
|
|---|
| 5529 |
|
|---|
| 5530 | #define PNG_NO_feature turns the feature off
|
|---|
| 5531 | #define PNG_feature_SUPPORTED turns the feature on
|
|---|
| 5532 |
|
|---|
| 5533 | pnglibconf.h contains one line for each feature macro which is either:
|
|---|
| 5534 |
|
|---|
| 5535 | #define PNG_feature_SUPPORTED
|
|---|
| 5536 |
|
|---|
| 5537 | if the feature is supported or:
|
|---|
| 5538 |
|
|---|
| 5539 | /*#undef PNG_feature_SUPPORTED*/
|
|---|
| 5540 |
|
|---|
| 5541 | if it is not. Library code consistently checks for the 'SUPPORTED' macro.
|
|---|
| 5542 | It does not, and libpng applications should not, check for the 'NO' macro
|
|---|
| 5543 | which will not normally be defined even if the feature is not supported.
|
|---|
| 5544 | The 'NO' macros are only used internally for setting or not setting the
|
|---|
| 5545 | corresponding 'SUPPORTED' macros.
|
|---|
| 5546 |
|
|---|
| 5547 | Compatibility with the old names is provided as follows:
|
|---|
| 5548 |
|
|---|
| 5549 | PNG_INCH_CONVERSIONS turns on PNG_INCH_CONVERSIONS_SUPPORTED
|
|---|
| 5550 |
|
|---|
| 5551 | And the following definitions disable the corresponding feature:
|
|---|
| 5552 |
|
|---|
| 5553 | PNG_SETJMP_NOT_SUPPORTED disables SETJMP
|
|---|
| 5554 | PNG_READ_TRANSFORMS_NOT_SUPPORTED disables READ_TRANSFORMS
|
|---|
| 5555 | PNG_NO_READ_COMPOSITED_NODIV disables READ_COMPOSITE_NODIV
|
|---|
| 5556 | PNG_WRITE_TRANSFORMS_NOT_SUPPORTED disables WRITE_TRANSFORMS
|
|---|
| 5557 | PNG_READ_ANCILLARY_CHUNKS_NOT_SUPPORTED disables READ_ANCILLARY_CHUNKS
|
|---|
| 5558 | PNG_WRITE_ANCILLARY_CHUNKS_NOT_SUPPORTED disables WRITE_ANCILLARY_CHUNKS
|
|---|
| 5559 |
|
|---|
| 5560 | Library builders should remove use of the above, inconsistent, names.
|
|---|
| 5561 |
|
|---|
| 5562 | 2) Warning and error message formatting was previously conditional on
|
|---|
| 5563 | the STDIO feature. The library has been changed to use the
|
|---|
| 5564 | CONSOLE_IO feature instead. This means that if CONSOLE_IO is disabled
|
|---|
| 5565 | the library no longer uses the printf(3) functions, even though the
|
|---|
| 5566 | default read/write implementations use (FILE) style stdio.h functions.
|
|---|
| 5567 |
|
|---|
| 5568 | 3) Three feature macros now control the fixed/floating point decisions:
|
|---|
| 5569 |
|
|---|
| 5570 | PNG_FLOATING_POINT_SUPPORTED enables the floating point APIs
|
|---|
| 5571 |
|
|---|
| 5572 | PNG_FIXED_POINT_SUPPORTED enables the fixed point APIs; however, in
|
|---|
| 5573 | practice these are normally required internally anyway (because the PNG
|
|---|
| 5574 | file format is fixed point), therefore in most cases PNG_NO_FIXED_POINT
|
|---|
| 5575 | merely stops the function from being exported.
|
|---|
| 5576 |
|
|---|
| 5577 | PNG_FLOATING_ARITHMETIC_SUPPORTED chooses between the internal floating
|
|---|
| 5578 | point implementation or the fixed point one. Typically the fixed point
|
|---|
| 5579 | implementation is larger and slower than the floating point implementation
|
|---|
| 5580 | on a system that supports floating point; however, it may be faster on a
|
|---|
| 5581 | system which lacks floating point hardware and therefore uses a software
|
|---|
| 5582 | emulation.
|
|---|
| 5583 |
|
|---|
| 5584 | 4) Added PNG_{READ,WRITE}_INT_FUNCTIONS_SUPPORTED. This allows the
|
|---|
| 5585 | functions to read and write ints to be disabled independently of
|
|---|
| 5586 | PNG_USE_READ_MACROS, which allows libpng to be built with the functions
|
|---|
| 5587 | even though the default is to use the macros - this allows applications
|
|---|
| 5588 | to choose at app buildtime whether or not to use macros (previously
|
|---|
| 5589 | impossible because the functions weren't in the default build.)
|
|---|
| 5590 |
|
|---|
| 5591 | .SH XII. Changes to Libpng from version 1.5.x to 1.6.x
|
|---|
| 5592 |
|
|---|
| 5593 | A "simplified API" has been added (see documentation in png.h and a simple
|
|---|
| 5594 | example in contrib/examples/pngtopng.c). The new publicly visible API
|
|---|
| 5595 | includes the following:
|
|---|
| 5596 |
|
|---|
| 5597 | macros:
|
|---|
| 5598 | PNG_FORMAT_*
|
|---|
| 5599 | PNG_IMAGE_*
|
|---|
| 5600 | structures:
|
|---|
| 5601 | png_control
|
|---|
| 5602 | png_image
|
|---|
| 5603 | read functions
|
|---|
| 5604 | png_image_begin_read_from_file()
|
|---|
| 5605 | png_image_begin_read_from_stdio()
|
|---|
| 5606 | png_image_begin_read_from_memory()
|
|---|
| 5607 | png_image_finish_read()
|
|---|
| 5608 | png_image_free()
|
|---|
| 5609 | write functions
|
|---|
| 5610 | png_image_write_to_file()
|
|---|
| 5611 | png_image_write_to_memory()
|
|---|
| 5612 | png_image_write_to_stdio()
|
|---|
| 5613 |
|
|---|
| 5614 | Starting with libpng-1.6.0, you can configure libpng to prefix all exported
|
|---|
| 5615 | symbols, using the PNG_PREFIX macro.
|
|---|
| 5616 |
|
|---|
| 5617 | We no longer include string.h in png.h. The include statement has been moved
|
|---|
| 5618 | to pngpriv.h, where it is not accessible by applications. Applications that
|
|---|
| 5619 | need access to information in string.h must add an '#include <string.h>'
|
|---|
| 5620 | directive. It does not matter whether this is placed prior to or after
|
|---|
| 5621 | the '#include "png.h"' directive.
|
|---|
| 5622 |
|
|---|
| 5623 | The following API are now DEPRECATED:
|
|---|
| 5624 | png_info_init_3()
|
|---|
| 5625 | png_convert_to_rfc1123() which has been replaced
|
|---|
| 5626 | with png_convert_to_rfc1123_buffer()
|
|---|
| 5627 | png_malloc_default()
|
|---|
| 5628 | png_free_default()
|
|---|
| 5629 | png_reset_zstream()
|
|---|
| 5630 |
|
|---|
| 5631 | The following have been removed:
|
|---|
| 5632 | png_get_io_chunk_name(), which has been replaced
|
|---|
| 5633 | with png_get_io_chunk_type(). The new
|
|---|
| 5634 | function returns a 32-bit integer instead of
|
|---|
| 5635 | a string.
|
|---|
| 5636 | The png_sizeof(), png_strlen(), png_memcpy(), png_memcmp(), and
|
|---|
| 5637 | png_memset() macros are no longer used in the libpng sources and
|
|---|
| 5638 | have been removed. These had already been made invisible to applications
|
|---|
| 5639 | (i.e., defined in the private pngpriv.h header file) since libpng-1.5.0.
|
|---|
| 5640 |
|
|---|
| 5641 | The signatures of many exported functions were changed, such that
|
|---|
| 5642 | png_structp became png_structrp or png_const_structrp
|
|---|
| 5643 | png_infop became png_inforp or png_const_inforp
|
|---|
| 5644 | where "rp" indicates a "restricted pointer".
|
|---|
| 5645 |
|
|---|
| 5646 | Dropped support for 16-bit platforms. The support for FAR/far types has
|
|---|
| 5647 | been eliminated and the definition of png_alloc_size_t is now controlled
|
|---|
| 5648 | by a flag so that 'small size_t' systems can select it if necessary.
|
|---|
| 5649 |
|
|---|
| 5650 | Error detection in some chunks has improved; in particular the iCCP chunk
|
|---|
| 5651 | reader now does pretty complete validation of the basic format. Some bad
|
|---|
| 5652 | profiles that were previously accepted are now accepted with a warning or
|
|---|
| 5653 | rejected, depending upon the png_set_benign_errors() setting, in particular
|
|---|
| 5654 | the very old broken Microsoft/HP 3144-byte sRGB profile. Starting with
|
|---|
| 5655 | libpng-1.6.11, recognizing and checking sRGB profiles can be avoided by
|
|---|
| 5656 | means of
|
|---|
| 5657 |
|
|---|
| 5658 | #if defined(PNG_SKIP_sRGB_CHECK_PROFILE) && \
|
|---|
| 5659 | defined(PNG_SET_OPTION_SUPPORTED)
|
|---|
| 5660 | png_set_option(png_ptr, PNG_SKIP_sRGB_CHECK_PROFILE,
|
|---|
| 5661 | PNG_OPTION_ON);
|
|---|
| 5662 | #endif
|
|---|
| 5663 |
|
|---|
| 5664 | It's not a good idea to do this if you are using the "simplified API",
|
|---|
| 5665 | which needs to be able to recognize sRGB profiles conveyed via the iCCP
|
|---|
| 5666 | chunk.
|
|---|
| 5667 |
|
|---|
| 5668 | The PNG spec requirement that only grayscale profiles may appear in images
|
|---|
| 5669 | with color type 0 or 4 and that even if the image only contains gray pixels,
|
|---|
| 5670 | only RGB profiles may appear in images with color type 2, 3, or 6, is now
|
|---|
| 5671 | enforced. The sRGB chunk is allowed to appear in images with any color type
|
|---|
| 5672 | and is interpreted by libpng to convey a one-tracer-curve gray profile or a
|
|---|
| 5673 | three-tracer-curve RGB profile as appropriate.
|
|---|
| 5674 |
|
|---|
| 5675 | Libpng 1.5.x erroneously used /MD for Debug DLL builds; if you used the debug
|
|---|
| 5676 | builds in your app and you changed your app to use /MD you will need to
|
|---|
| 5677 | change it back to /MDd for libpng 1.6.x.
|
|---|
| 5678 |
|
|---|
| 5679 | Prior to libpng-1.6.0 a warning would be issued if the iTXt chunk contained
|
|---|
| 5680 | an empty language field or an empty translated keyword. Both of these
|
|---|
| 5681 | are allowed by the PNG specification, so these warnings are no longer issued.
|
|---|
| 5682 |
|
|---|
| 5683 | The library now issues an error if the application attempts to set a
|
|---|
| 5684 | transform after it calls png_read_update_info() or if it attempts to call
|
|---|
| 5685 | both png_read_update_info() and png_start_read_image() or to call either
|
|---|
| 5686 | of them more than once.
|
|---|
| 5687 |
|
|---|
| 5688 | The default condition for benign_errors is now to treat benign errors as
|
|---|
| 5689 | warnings while reading and as errors while writing.
|
|---|
| 5690 |
|
|---|
| 5691 | The library now issues a warning if both background processing and RGB to
|
|---|
| 5692 | gray are used when gamma correction happens. As with previous versions of
|
|---|
| 5693 | the library the results are numerically very incorrect in this case.
|
|---|
| 5694 |
|
|---|
| 5695 | There are some minor arithmetic changes in some transforms such as
|
|---|
| 5696 | png_set_background(), that might be detected by certain regression tests.
|
|---|
| 5697 |
|
|---|
| 5698 | Unknown chunk handling has been improved internally, without any API change.
|
|---|
| 5699 | This adds more correct option control of the unknown handling, corrects
|
|---|
| 5700 | a pre-existing bug where the per-chunk 'keep' setting is ignored, and makes
|
|---|
| 5701 | it possible to skip IDAT chunks in the sequential reader.
|
|---|
| 5702 |
|
|---|
| 5703 | The machine-generated configure files are no longer included in branches
|
|---|
| 5704 | libpng16 and later of the GIT repository. They continue to be included
|
|---|
| 5705 | in the tarball releases, however.
|
|---|
| 5706 |
|
|---|
| 5707 | Libpng-1.6.0 through 1.6.2 used the CMF bytes at the beginning of the IDAT
|
|---|
| 5708 | stream to set the size of the sliding window for reading instead of using the
|
|---|
| 5709 | default 32-kbyte sliding window size. It was discovered that there are
|
|---|
| 5710 | hundreds of PNG files in the wild that have incorrect CMF bytes that caused
|
|---|
| 5711 | zlib to issue the "invalid distance too far back" error and reject the file.
|
|---|
| 5712 | Libpng-1.6.3 and later calculate their own safe CMF from the image dimensions,
|
|---|
| 5713 | provide a way to revert to the libpng-1.5.x behavior (ignoring the CMF bytes
|
|---|
| 5714 | and using a 32-kbyte sliding window), by using
|
|---|
| 5715 |
|
|---|
| 5716 | png_set_option(png_ptr, PNG_MAXIMUM_INFLATE_WINDOW,
|
|---|
| 5717 | PNG_OPTION_ON);
|
|---|
| 5718 |
|
|---|
| 5719 | and provide a tool (contrib/tools/pngfix) for rewriting a PNG file while
|
|---|
| 5720 | optimizing the CMF bytes in its IDAT chunk correctly.
|
|---|
| 5721 |
|
|---|
| 5722 | Libpng-1.6.0 and libpng-1.6.1 wrote uncompressed iTXt chunks with the wrong
|
|---|
| 5723 | length, which resulted in PNG files that cannot be read beyond the bad iTXt
|
|---|
| 5724 | chunk. This error was fixed in libpng-1.6.3, and a tool (called
|
|---|
| 5725 | contrib/tools/png-fix-itxt) has been added to the libpng distribution.
|
|---|
| 5726 |
|
|---|
| 5727 | Starting with libpng-1.6.17, the PNG_SAFE_LIMITS macro was eliminated
|
|---|
| 5728 | and safe limits are used by default (users who need larger limits
|
|---|
| 5729 | can still override them at compile time or run time, as described above).
|
|---|
| 5730 |
|
|---|
| 5731 | The new limits are
|
|---|
| 5732 | default spec limit
|
|---|
| 5733 | png_user_width_max 1,000,000 2,147,483,647
|
|---|
| 5734 | png_user_height_max 1,000,000 2,147,483,647
|
|---|
| 5735 | png_user_chunk_cache_max 128 unlimited
|
|---|
| 5736 | png_user_chunk_malloc_max 8,000,000 unlimited
|
|---|
| 5737 |
|
|---|
| 5738 | Starting with libpng-1.6.18, a PNG_RELEASE_BUILD macro was added, which allows
|
|---|
| 5739 | library builders to control compilation for an installed system (a release build).
|
|---|
| 5740 | It can be set for testing debug or beta builds to ensure that they will compile
|
|---|
| 5741 | when the build type is switched to RC or STABLE. In essence this overrides the
|
|---|
| 5742 | PNG_LIBPNG_BUILD_BASE_TYPE definition which is not directly user controllable.
|
|---|
| 5743 |
|
|---|
| 5744 | Starting with libpng-1.6.19, attempting to set an over-length PLTE chunk
|
|---|
| 5745 | is an error. Previously this requirement of the PNG specification was not
|
|---|
| 5746 | enforced, and the palette was always limited to 256 entries. An over-length
|
|---|
| 5747 | PLTE chunk found in an input PNG is silently truncated.
|
|---|
| 5748 |
|
|---|
| 5749 | Starting with libpng-1.6.31, the eXIf chunk is supported. Libpng does not
|
|---|
| 5750 | attempt to decode the Exif profile; it simply returns a byte array
|
|---|
| 5751 | containing the profile to the calling application which must do its own
|
|---|
| 5752 | decoding.
|
|---|
| 5753 |
|
|---|
| 5754 | .SH XIII. Detecting libpng
|
|---|
| 5755 |
|
|---|
| 5756 | The png_get_io_ptr() function has been present since libpng-0.88, has never
|
|---|
| 5757 | changed, and is unaffected by conditional compilation macros. It is the
|
|---|
| 5758 | best choice for use in configure scripts for detecting the presence of any
|
|---|
| 5759 | libpng version since 0.88. In an autoconf "configure.in" you could use
|
|---|
| 5760 |
|
|---|
| 5761 | AC_CHECK_LIB(png, png_get_io_ptr, ...
|
|---|
| 5762 |
|
|---|
| 5763 | .SH XV. Source code repository
|
|---|
| 5764 |
|
|---|
| 5765 | Since about February 2009, version 1.2.34, libpng has been under "git" source
|
|---|
| 5766 | control. The git repository was built from old libpng-x.y.z.tar.gz files
|
|---|
| 5767 | going back to version 0.70. You can access the git repository (read only)
|
|---|
| 5768 | at
|
|---|
| 5769 |
|
|---|
| 5770 | https://github.com/glennrp/libpng or
|
|---|
| 5771 | https://git.code.sf.net/p/libpng/code.git
|
|---|
| 5772 |
|
|---|
| 5773 | or you can browse it with a web browser at
|
|---|
| 5774 |
|
|---|
| 5775 | https://github.com/glennrp/libpng or
|
|---|
| 5776 | https://sourceforge.net/p/libpng/code/ci/libpng16/tree/
|
|---|
| 5777 |
|
|---|
| 5778 | Patches can be sent to png-mng-implement at lists.sourceforge.net or
|
|---|
| 5779 | uploaded to the libpng bug tracker at
|
|---|
| 5780 |
|
|---|
| 5781 | https://libpng.sourceforge.io/
|
|---|
| 5782 |
|
|---|
| 5783 | or as a "pull request" to
|
|---|
| 5784 |
|
|---|
| 5785 | https://github.com/glennrp/libpng/pulls
|
|---|
| 5786 |
|
|---|
| 5787 | We also accept patches built from the tar or zip distributions, and
|
|---|
| 5788 | simple verbal descriptions of bug fixes, reported either to the
|
|---|
| 5789 | SourceForge bug tracker, to the png-mng-implement at lists.sf.net
|
|---|
| 5790 | mailing list, as github issues.
|
|---|
| 5791 |
|
|---|
| 5792 | .SH XV. Coding style
|
|---|
| 5793 |
|
|---|
| 5794 | Our coding style is similar to the "Allman" style
|
|---|
| 5795 | (See https://en.wikipedia.org/wiki/Indent_style#Allman_style), with curly
|
|---|
| 5796 | braces on separate lines:
|
|---|
| 5797 |
|
|---|
| 5798 | if (condition)
|
|---|
| 5799 | {
|
|---|
| 5800 | action;
|
|---|
| 5801 | }
|
|---|
| 5802 |
|
|---|
| 5803 | else if (another condition)
|
|---|
| 5804 | {
|
|---|
| 5805 | another action;
|
|---|
| 5806 | }
|
|---|
| 5807 |
|
|---|
| 5808 | The braces can be omitted from simple one-line actions:
|
|---|
| 5809 |
|
|---|
| 5810 | if (condition)
|
|---|
| 5811 | return 0;
|
|---|
| 5812 |
|
|---|
| 5813 | We use 3-space indentation, except for continued statements which
|
|---|
| 5814 | are usually indented the same as the first line of the statement
|
|---|
| 5815 | plus four more spaces.
|
|---|
| 5816 |
|
|---|
| 5817 | For macro definitions we use 2-space indentation, always leaving the "#"
|
|---|
| 5818 | in the first column.
|
|---|
| 5819 |
|
|---|
| 5820 | #ifndef PNG_NO_FEATURE
|
|---|
| 5821 | # ifndef PNG_FEATURE_SUPPORTED
|
|---|
| 5822 | # define PNG_FEATURE_SUPPORTED
|
|---|
| 5823 | # endif
|
|---|
| 5824 | #endif
|
|---|
| 5825 |
|
|---|
| 5826 | Comments appear with the leading "/*" at the same indentation as
|
|---|
| 5827 | the statement that follows the comment:
|
|---|
| 5828 |
|
|---|
| 5829 | /* Single-line comment */
|
|---|
| 5830 | statement;
|
|---|
| 5831 |
|
|---|
| 5832 | /* This is a multiple-line
|
|---|
| 5833 | * comment.
|
|---|
| 5834 | */
|
|---|
| 5835 | statement;
|
|---|
| 5836 |
|
|---|
| 5837 | Very short comments can be placed after the end of the statement
|
|---|
| 5838 | to which they pertain:
|
|---|
| 5839 |
|
|---|
| 5840 | statement; /* comment */
|
|---|
| 5841 |
|
|---|
| 5842 | We don't use C++ style ("//") comments. We have, however,
|
|---|
| 5843 | used them in the past in some now-abandoned MMX assembler
|
|---|
| 5844 | code.
|
|---|
| 5845 |
|
|---|
| 5846 | Functions and their curly braces are not indented, and
|
|---|
| 5847 | exported functions are marked with PNGAPI:
|
|---|
| 5848 |
|
|---|
| 5849 | /* This is a public function that is visible to
|
|---|
| 5850 | * application programmers. It does thus-and-so.
|
|---|
| 5851 | */
|
|---|
| 5852 | void PNGAPI
|
|---|
| 5853 | png_exported_function(png_ptr, png_info, foo)
|
|---|
| 5854 | {
|
|---|
| 5855 | body;
|
|---|
| 5856 | }
|
|---|
| 5857 |
|
|---|
| 5858 | The return type and decorations are placed on a separate line
|
|---|
| 5859 | ahead of the function name, as illustrated above.
|
|---|
| 5860 |
|
|---|
| 5861 | The prototypes for all exported functions appear in png.h,
|
|---|
| 5862 | above the comment that says
|
|---|
| 5863 |
|
|---|
| 5864 | /* Maintainer: Put new public prototypes here ... */
|
|---|
| 5865 |
|
|---|
| 5866 | We mark all non-exported functions with "/* PRIVATE */"":
|
|---|
| 5867 |
|
|---|
| 5868 | void /* PRIVATE */
|
|---|
| 5869 | png_non_exported_function(png_ptr, png_info, foo)
|
|---|
| 5870 | {
|
|---|
| 5871 | body;
|
|---|
| 5872 | }
|
|---|
| 5873 |
|
|---|
| 5874 | The prototypes for non-exported functions (except for those in
|
|---|
| 5875 | pngtest) appear in pngpriv.h above the comment that says
|
|---|
| 5876 |
|
|---|
| 5877 | /* Maintainer: Put new private prototypes here ^ */
|
|---|
| 5878 |
|
|---|
| 5879 | To avoid polluting the global namespace, the names of all exported
|
|---|
| 5880 | functions and variables begin with "png_", and all publicly visible C
|
|---|
| 5881 | preprocessor macros begin with "PNG". We request that applications that
|
|---|
| 5882 | use libpng *not* begin any of their own symbols with either of these strings.
|
|---|
| 5883 |
|
|---|
| 5884 | We put a space after the "sizeof" operator and we omit the
|
|---|
| 5885 | optional parentheses around its argument when the argument
|
|---|
| 5886 | is an expression, not a type name, and we always enclose the
|
|---|
| 5887 | sizeof operator, with its argument, in parentheses:
|
|---|
| 5888 |
|
|---|
| 5889 | (sizeof (png_uint_32))
|
|---|
| 5890 | (sizeof array)
|
|---|
| 5891 |
|
|---|
| 5892 | Prior to libpng-1.6.0 we used a "png_sizeof()" macro, formatted as
|
|---|
| 5893 | though it were a function.
|
|---|
| 5894 |
|
|---|
| 5895 | Control keywords if, for, while, and switch are always followed by a space
|
|---|
| 5896 | to distinguish them from function calls, which have no trailing space.
|
|---|
| 5897 |
|
|---|
| 5898 | We put a space after each comma and after each semicolon
|
|---|
| 5899 | in "for" statements, and we put spaces before and after each
|
|---|
| 5900 | C binary operator and after "for" or "while", and before
|
|---|
| 5901 | "?". We don't put a space between a typecast and the expression
|
|---|
| 5902 | being cast, nor do we put one between a function name and the
|
|---|
| 5903 | left parenthesis that follows it:
|
|---|
| 5904 |
|
|---|
| 5905 | for (i = 2; i > 0; \-\-i)
|
|---|
| 5906 | y[i] = a(x) + (int)b;
|
|---|
| 5907 |
|
|---|
| 5908 | We prefer #ifdef and #ifndef to #if defined() and #if !defined()
|
|---|
| 5909 | when there is only one macro being tested. We always use parentheses
|
|---|
| 5910 | with "defined".
|
|---|
| 5911 |
|
|---|
| 5912 | We express integer constants that are used as bit masks in hex format,
|
|---|
| 5913 | with an even number of lower-case hex digits, and to make them unsigned
|
|---|
| 5914 | (e.g., 0x00U, 0xffU, 0x0100U) and long if they are greater than 0x7fff
|
|---|
| 5915 | (e.g., 0xffffUL).
|
|---|
| 5916 |
|
|---|
| 5917 | We prefer to use underscores rather than camelCase in names, except
|
|---|
| 5918 | for a few type names that we inherit from zlib.h.
|
|---|
| 5919 |
|
|---|
| 5920 | We prefer "if (something != 0)" and "if (something == 0)" over
|
|---|
| 5921 | "if (something)" and if "(!something)", respectively, and for pointers
|
|---|
| 5922 | we prefer "if (some_pointer != NULL)" or "if (some_pointer == NULL)".
|
|---|
| 5923 |
|
|---|
| 5924 | We do not use the TAB character for indentation in the C sources.
|
|---|
| 5925 |
|
|---|
| 5926 | Lines do not exceed 80 characters.
|
|---|
| 5927 |
|
|---|
| 5928 | Other rules can be inferred by inspecting the libpng source.
|
|---|
| 5929 |
|
|---|
| 5930 | .SH NOTE
|
|---|
| 5931 |
|
|---|
| 5932 | Note about libpng version numbers:
|
|---|
| 5933 |
|
|---|
| 5934 | Due to various miscommunications, unforeseen code incompatibilities
|
|---|
| 5935 | and occasional factors outside the authors' control, version numbering
|
|---|
| 5936 | on the library has not always been consistent and straightforward.
|
|---|
| 5937 | The following table summarizes matters since version 0.89c, which was
|
|---|
| 5938 | the first widely used release:
|
|---|
| 5939 |
|
|---|
| 5940 | source png.h png.h shared-lib
|
|---|
| 5941 | version string int version
|
|---|
| 5942 | ------- ------ ----- ----------
|
|---|
| 5943 | 0.89c "1.0 beta 3" 0.89 89 1.0.89
|
|---|
| 5944 | 0.90 "1.0 beta 4" 0.90 90 0.90 [should have been 2.0.90]
|
|---|
| 5945 | 0.95 "1.0 beta 5" 0.95 95 0.95 [should have been 2.0.95]
|
|---|
| 5946 | 0.96 "1.0 beta 6" 0.96 96 0.96 [should have been 2.0.96]
|
|---|
| 5947 | 0.97b "1.00.97 beta 7" 1.00.97 97 1.0.1 [should have been 2.0.97]
|
|---|
| 5948 | 0.97c 0.97 97 2.0.97
|
|---|
| 5949 | 0.98 0.98 98 2.0.98
|
|---|
| 5950 | 0.99 0.99 98 2.0.99
|
|---|
| 5951 | 0.99a-m 0.99 99 2.0.99
|
|---|
| 5952 | 1.00 1.00 100 2.1.0 [100 should be 10000]
|
|---|
| 5953 | 1.0.0 (from here on, the 100 2.1.0 [100 should be 10000]
|
|---|
| 5954 | 1.0.1 png.h string is 10001 2.1.0
|
|---|
| 5955 | 1.0.1a-e identical to the 10002 from here on, the shared library
|
|---|
| 5956 | 1.0.2 source version) 10002 is 2.V where V is the source code
|
|---|
| 5957 | 1.0.2a-b 10003 version, except as noted.
|
|---|
| 5958 | 1.0.3 10003
|
|---|
| 5959 | 1.0.3a-d 10004
|
|---|
| 5960 | 1.0.4 10004
|
|---|
| 5961 | 1.0.4a-f 10005
|
|---|
| 5962 | 1.0.5 (+ 2 patches) 10005
|
|---|
| 5963 | 1.0.5a-d 10006
|
|---|
| 5964 | 1.0.5e-r 10100 (not source compatible)
|
|---|
| 5965 | 1.0.5s-v 10006 (not binary compatible)
|
|---|
| 5966 | 1.0.6 (+ 3 patches) 10006 (still binary incompatible)
|
|---|
| 5967 | 1.0.6d-f 10007 (still binary incompatible)
|
|---|
| 5968 | 1.0.6g 10007
|
|---|
| 5969 | 1.0.6h 10007 10.6h (testing xy.z so-numbering)
|
|---|
| 5970 | 1.0.6i 10007 10.6i
|
|---|
| 5971 | 1.0.6j 10007 2.1.0.6j (incompatible with 1.0.0)
|
|---|
| 5972 | 1.0.7beta11-14 DLLNUM 10007 2.1.0.7beta11-14 (binary compatible)
|
|---|
| 5973 | 1.0.7beta15-18 1 10007 2.1.0.7beta15-18 (binary compatible)
|
|---|
| 5974 | 1.0.7rc1-2 1 10007 2.1.0.7rc1-2 (binary compatible)
|
|---|
| 5975 | 1.0.7 1 10007 (still compatible)
|
|---|
| 5976 | ...
|
|---|
| 5977 | 1.0.69 10 10069 10.so.0.69[.0]
|
|---|
| 5978 | ...
|
|---|
| 5979 | 1.2.59 13 10259 12.so.0.59[.0]
|
|---|
| 5980 | ...
|
|---|
| 5981 | 1.4.20 14 10420 14.so.0.20[.0]
|
|---|
| 5982 | ...
|
|---|
| 5983 | 1.5.30 15 10530 15.so.15.30[.0]
|
|---|
| 5984 | ...
|
|---|
| 5985 | 1.6.35 16 10635 16.so.16.35[.0]
|
|---|
| 5986 |
|
|---|
| 5987 | Henceforth the source version will match the shared-library minor and
|
|---|
| 5988 | patch numbers; the shared-library major version number will be used for
|
|---|
| 5989 | changes in backward compatibility, as it is intended.
|
|---|
| 5990 | The PNG_PNGLIB_VER macro, which is not used within libpng but is
|
|---|
| 5991 | available for applications, is an unsigned integer of the form XYYZZ
|
|---|
| 5992 | corresponding to the source version X.Y.Z (leading zeros in Y and Z).
|
|---|
| 5993 | Beta versions were given the previous public release number plus a
|
|---|
| 5994 | letter, until version 1.0.6j; from then on they were given the upcoming
|
|---|
| 5995 | public release number plus "betaNN" or "rcNN".
|
|---|
| 5996 |
|
|---|
| 5997 | .SH "SEE ALSO"
|
|---|
| 5998 | .IR libpngpf(3) ", " png(5)
|
|---|
| 5999 | .LP
|
|---|
| 6000 | .IR libpng :
|
|---|
| 6001 | .IP
|
|---|
| 6002 | https://libpng.sourceforge.io/ (follow the [DOWNLOAD] link)
|
|---|
| 6003 | http://www.libpng.org/pub/png
|
|---|
| 6004 |
|
|---|
| 6005 | .LP
|
|---|
| 6006 | .IR zlib :
|
|---|
| 6007 | .IP
|
|---|
| 6008 | (generally) at the same location as
|
|---|
| 6009 | .I libpng
|
|---|
| 6010 | or at
|
|---|
| 6011 | .br
|
|---|
| 6012 | https://zlib.net/
|
|---|
| 6013 |
|
|---|
| 6014 | .LP
|
|---|
| 6015 | .IR PNG specification: RFC 2083
|
|---|
| 6016 | .IP
|
|---|
| 6017 | (generally) at the same location as
|
|---|
| 6018 | .I libpng
|
|---|
| 6019 | or at
|
|---|
| 6020 | .br
|
|---|
| 6021 | https://www.ietf.org/rfc/rfc2083.txt
|
|---|
| 6022 | .br
|
|---|
| 6023 | or (as a W3C Recommendation) at
|
|---|
| 6024 | .br
|
|---|
| 6025 | https://www.w3.org/TR/REC-png.html
|
|---|
| 6026 |
|
|---|
| 6027 | .LP
|
|---|
| 6028 | In the case of any inconsistency between the PNG specification
|
|---|
| 6029 | and this library, the specification takes precedence.
|
|---|
| 6030 |
|
|---|
| 6031 | .SH AUTHORS
|
|---|
| 6032 | This man page:
|
|---|
| 6033 | Initially created by Glenn Randers-Pehrson.
|
|---|
| 6034 | Maintained by Cosmin Truta.
|
|---|
| 6035 |
|
|---|
| 6036 | The contributing authors would like to thank all those who helped
|
|---|
| 6037 | with testing, bug fixes, and patience. This wouldn't have been
|
|---|
| 6038 | possible without all of you.
|
|---|
| 6039 |
|
|---|
| 6040 | Thanks to Frank J. T. Wojcik for helping with the documentation.
|
|---|
| 6041 |
|
|---|
| 6042 | Libpng:
|
|---|
| 6043 | Initially created in 1995 by Guy Eric Schalnat, then of Group 42, Inc.
|
|---|
| 6044 | Maintained by Cosmin Truta.
|
|---|
| 6045 |
|
|---|
| 6046 | Supported by the PNG development group
|
|---|
| 6047 | .br
|
|---|
| 6048 | png-mng-implement at lists.sourceforge.net (subscription required; visit
|
|---|
| 6049 | https://lists.sourceforge.net/lists/listinfo/png-mng-implement
|
|---|
| 6050 | to subscribe).
|
|---|
| 6051 |
|
|---|
| 6052 | .\" end of man page
|
|---|
