| 1 | .TH LIBPNG 3 "November 12, 2015"
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| 2 | .SH NAME
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| 3 | libpng \- Portable Network Graphics (PNG) Reference Library 1.2.54
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| 4 | .SH SYNOPSIS
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| 5 | \fB
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| 6 | #include <png.h>\fP
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| 7 |
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| 8 | \fBpng_uint_32 png_access_version_number \fI(void\fP\fB);\fP
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| 9 |
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| 10 | \fBint png_check_sig (png_bytep \fP\fIsig\fP\fB, int \fInum\fP\fB);\fP
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| 11 |
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| 12 | \fBvoid png_chunk_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
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| 13 |
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| 14 | \fBvoid png_chunk_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
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| 15 |
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| 16 | \fBvoid png_convert_from_struct_tm (png_timep \fP\fIptime\fP\fB, struct tm FAR * \fIttime\fP\fB);\fP
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| 17 |
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| 18 | \fBvoid png_convert_from_time_t (png_timep \fP\fIptime\fP\fB, time_t \fIttime\fP\fB);\fP
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| 19 |
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| 20 | \fBpng_charp png_convert_to_rfc1123 (png_structp \fP\fIpng_ptr\fP\fB, png_timep \fIptime\fP\fB);\fP
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| 21 |
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| 22 | \fBpng_infop png_create_info_struct (png_structp \fIpng_ptr\fP\fB);\fP
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| 23 |
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| 24 | \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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| 25 |
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| 26 | \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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| 27 |
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| 28 | \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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| 29 |
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| 30 | \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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| 31 |
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| 32 | \fBint png_debug(int \fP\fIlevel\fP\fB, png_const_charp \fImessage\fP\fB);\fP
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| 33 |
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| 34 | \fBint png_debug1(int \fP\fIlevel\fP\fB, png_const_charp \fP\fImessage\fP\fB, \fIp1\fP\fB);\fP
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| 35 |
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| 36 | \fBint png_debug2(int \fP\fIlevel\fP\fB, png_const_charp \fP\fImessage\fP\fB, \fP\fIp1\fP\fB, \fIp2\fP\fB);\fP
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| 37 |
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| 38 | \fBvoid png_destroy_info_struct (png_structp \fP\fIpng_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
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| 39 |
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| 40 | \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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| 41 |
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| 42 | \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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| 43 |
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| 44 | \fBvoid png_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
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| 45 |
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| 46 | \fBvoid png_free (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
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| 47 |
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| 48 | \fBvoid png_free_chunk_list (png_structp \fIpng_ptr\fP\fB);\fP
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| 49 |
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| 50 | \fBvoid png_free_default(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_data (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fInum\fP\fB);\fP
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| 53 |
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| 54 | \fBpng_byte png_get_bit_depth (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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| 55 |
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| 56 | \fBpng_uint_32 png_get_bKGD (png_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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| 57 |
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| 58 | \fBpng_byte png_get_channels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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| 59 |
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| 60 | \fBpng_uint_32 png_get_cHRM (png_structp \fP\fIpng_ptr\fP\fB, png_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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| 61 |
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| 62 | \fBpng_uint_32 png_get_cHRM_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_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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| 63 |
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| 64 | \fBpng_byte png_get_color_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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| 65 |
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| 66 | \fBpng_byte png_get_compression_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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| 67 |
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| 68 | \fBpng_byte png_get_copyright (png_structp \fIpng_ptr\fP\fB);\fP
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| 69 |
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| 70 | \fBpng_voidp png_get_error_ptr (png_structp \fIpng_ptr\fP\fB);\fP
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| 71 |
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| 72 | \fBpng_byte png_get_filter_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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| 73 |
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| 74 | \fBpng_uint_32 png_get_gAMA (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fI*file_gamma\fP\fB);\fP
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| 75 |
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| 76 | \fBpng_uint_32 png_get_gAMA_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fI*int_file_gamma\fP\fB);\fP
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| 77 |
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| 78 | \fBpng_byte png_get_header_ver (png_structp \fIpng_ptr\fP\fB);\fP
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| 79 |
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| 80 | \fBpng_byte png_get_header_version (png_structp \fIpng_ptr\fP\fB);\fP
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| 81 |
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| 82 | \fBpng_uint_32 png_get_hIST (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_16p \fI*hist\fP\fB);\fP
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| 83 |
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| 84 | \fBpng_uint_32 png_get_iCCP (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charpp \fP\fIname\fP\fB, int \fP\fI*compression_type\fP\fB, png_charpp \fP\fIprofile\fP\fB, png_uint_32 \fI*proflen\fP\fB);\fP
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| 85 |
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| 86 | \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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| 87 |
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| 88 | \fBpng_uint_32 png_get_image_height (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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| 89 |
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| 90 | \fBpng_uint_32 png_get_image_width (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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| 91 |
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| 92 | \fB#if !defined(PNG_1_0_X) png_int_32 png_get_int_32 (png_bytep buf); \fI#endif
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| 93 |
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| 94 | \fBpng_byte png_get_interlace_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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| 95 |
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| 96 | \fBpng_voidp png_get_io_ptr (png_structp \fIpng_ptr\fP\fB);\fP
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| 97 |
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| 98 | \fBpng_byte png_get_libpng_ver (png_structp \fIpng_ptr\fP\fB);\fP
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| 99 |
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| 100 | \fBpng_voidp png_get_mem_ptr(png_structp \fIpng_ptr\fP\fB);\fP
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| 101 |
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| 102 | \fBpng_uint_32 png_get_oFFs (png_structp \fP\fIpng_ptr\fP\fB, png_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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| 103 |
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| 104 | \fBpng_uint_32 png_get_pCAL (png_structp \fP\fIpng_ptr\fP\fB, png_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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| 105 |
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| 106 | \fBpng_uint_32 png_get_pHYs (png_structp \fP\fIpng_ptr\fP\fB, png_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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| 107 |
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| 108 | \fBfloat png_get_pixel_aspect_ratio (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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| 109 |
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| 110 | \fBpng_uint_32 png_get_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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| 111 |
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| 112 | \fBpng_voidp png_get_progressive_ptr (png_structp \fIpng_ptr\fP\fB);\fP
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| 113 |
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| 114 | \fBpng_uint_32 png_get_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_colorp \fP\fI*palette\fP\fB, int \fI*num_palette\fP\fB);\fP
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| 115 |
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| 116 | \fBpng_byte png_get_rgb_to_gray_status (png_structp png_ptr) png_uint_32 png_get_rowbytes (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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| 117 |
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| 118 | \fBpng_bytepp png_get_rows (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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| 119 |
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| 120 | \fBpng_uint_32 png_get_sBIT (png_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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| 121 |
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| 122 | \fBpng_bytep png_get_signature (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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| 123 |
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| 124 | \fBpng_uint_32 png_get_sPLT (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_spalette_p \fI*splt_ptr\fP\fB);\fP
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| 125 |
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| 126 | \fBpng_uint_32 png_get_sRGB (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fI*intent\fP\fB);\fP
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| 127 |
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| 128 | \fBpng_uint_32 png_get_text (png_structp \fP\fIpng_ptr\fP\fB, png_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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| 129 |
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| 130 | \fBpng_uint_32 png_get_tIME (png_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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| 131 |
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| 132 | \fBpng_uint_32 png_get_tRNS (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fI*trans\fP\fB, int \fP\fI*num_trans\fP\fB, png_color_16p \fI*trans_values\fP\fB);\fP
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| 133 |
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| 134 | \fB#if !defined(PNG_1_0_X) png_uint_16 png_get_uint_16 (png_bytep \fIbuf\fP\fB);\fP
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| 135 |
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| 136 | \fBpng_uint_32 png_get_uint_31 (png_bytep \fIbuf\fP\fB);\fP
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| 137 |
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| 138 | \fBpng_uint_32 png_get_uint_32 (png_bytep buf); \fI#endif
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| 139 |
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| 140 | \fBpng_uint_32 png_get_unknown_chunks (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_unknown_chunkpp \fIunknowns\fP\fB);\fP
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| 141 |
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| 142 | \fBpng_voidp png_get_user_chunk_ptr (png_structp \fIpng_ptr\fP\fB);\fP
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| 143 |
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| 144 | \fBpng_uint_32 png_get_user_height_max( png_structp \fIpng_ptr\fP\fB);\fP
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| 145 |
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| 146 | \fBpng_voidp png_get_user_transform_ptr (png_structp \fIpng_ptr\fP\fB);\fP
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| 147 |
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| 148 | \fBpng_uint_32 png_get_user_width_max (png_structp \fIpng_ptr\fP\fB);\fP
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| 149 |
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| 150 | \fBpng_uint_32 png_get_valid (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fIflag\fP\fB);\fP
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| 151 |
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| 152 | \fBpng_int_32 png_get_x_offset_microns (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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| 153 |
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| 154 | \fBpng_int_32 png_get_x_offset_pixels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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| 155 |
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| 156 | \fBpng_uint_32 png_get_x_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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| 157 |
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| 158 | \fBpng_int_32 png_get_y_offset_microns (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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| 159 |
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| 160 | \fBpng_int_32 png_get_y_offset_pixels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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| 161 |
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| 162 | \fBpng_uint_32 png_get_y_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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| 163 |
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| 164 | \fBpng_uint_32 png_get_compression_buffer_size (png_structp \fIpng_ptr\fP\fB);\fP
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| 165 |
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| 166 | \fBint png_handle_as_unknown (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIchunk_name\fP\fB);\fP
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| 167 |
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| 168 | \fBvoid png_init_io (png_structp \fP\fIpng_ptr\fP\fB, FILE \fI*fp\fP\fB);\fP
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| 169 |
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| 170 | \fBDEPRECATED void png_info_init (png_infop \fIinfo_ptr\fP\fB);\fP
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| 171 |
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| 172 | \fBDEPRECATED void png_info_init_2 (png_infopp \fP\fIptr_ptr\fP\fB, png_size_t \fIpng_info_struct_size\fP\fB);\fP
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| 173 |
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| 174 | \fBpng_voidp png_malloc (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
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| 175 |
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| 176 | \fBpng_voidp png_malloc_default(png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
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| 177 |
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| 178 | \fBvoidp png_memcpy (png_voidp \fP\fIs1\fP\fB, png_voidp \fP\fIs2\fP\fB, png_size_t \fIsize\fP\fB);\fP
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| 179 |
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| 180 | \fBpng_voidp png_memcpy_check (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIs1\fP\fB, png_voidp \fP\fIs2\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
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| 181 |
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| 182 | \fBvoidp png_memset (png_voidp \fP\fIs1\fP\fB, int \fP\fIvalue\fP\fB, png_size_t \fIsize\fP\fB);\fP
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| 183 |
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| 184 | \fBpng_voidp png_memset_check (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIs1\fP\fB, int \fP\fIvalue\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
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| 185 |
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| 186 | \fBDEPRECATED void png_permit_empty_plte (png_structp \fP\fIpng_ptr\fP\fB, int \fIempty_plte_permitted\fP\fB);\fP
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| 187 |
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| 188 | \fBvoid png_process_data (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fIbuffer\fP\fB, png_size_t \fIbuffer_size\fP\fB);\fP
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| 189 |
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| 190 | \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
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| 191 |
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| 192 | \fBvoid png_read_destroy (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_infop \fIend_info_ptr\fP\fB);\fP
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| 193 |
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| 194 | \fBvoid png_read_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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| 195 |
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| 196 | \fBvoid png_read_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
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| 197 |
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| 198 | \fBDEPRECATED void png_read_init (png_structp \fIpng_ptr\fP\fB);\fP
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| 199 |
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| 200 | \fBDEPRECATED void png_read_init_2 (png_structpp \fP\fIptr_ptr\fP\fB, png_const_charp \fP\fIuser_png_ver\fP\fB, png_size_t \fP\fIpng_struct_size\fP\fB, png_size_t \fIpng_info_size\fP\fB);\fP
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| 201 |
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| 202 | \fBvoid png_read_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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| 203 |
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| 204 | \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
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| 205 |
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| 206 | \fBvoid png_read_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIrow\fP\fB, png_bytep \fIdisplay_row\fP\fB);\fP
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| 207 |
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| 208 | \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
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| 209 |
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| 210 | \fBvoid png_read_update_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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| 211 |
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| 212 | \fB#if !defined(PNG_1_0_X) png_save_int_32 (png_bytep \fP\fIbuf\fP\fB, png_int_32 \fIi\fP\fB);\fP
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| 213 |
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| 214 | \fBvoid png_save_uint_16 (png_bytep \fP\fIbuf\fP\fB, unsigned int \fIi\fP\fB);\fP
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| 215 |
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| 216 | \fBvoid png_save_uint_32 (png_bytep \fP\fIbuf\fP\fB, png_uint_32 \fIi\fP\fB);\fP
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| 217 |
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| 218 | \fBvoid png_set_add_alpha (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int flags); \fI#endif
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| 219 |
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| 220 | \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
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| 221 |
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| 222 | \fBvoid png_set_bgr (png_structp \fIpng_ptr\fP\fB);\fP
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| 223 |
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| 224 | \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
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| 225 |
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| 226 | \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
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| 227 |
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| 228 | \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
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| 229 |
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| 230 | \fBvoid png_set_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP
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| 231 |
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| 232 | \fBvoid png_set_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP
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| 233 |
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| 234 | \fBvoid png_set_compression_method (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod\fP\fB);\fP
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| 235 |
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| 236 | \fBvoid png_set_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP
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| 237 |
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| 238 | \fBvoid png_set_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP
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| 239 |
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| 240 | \fBvoid png_set_crc_action (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIcrit_action\fP\fB, int \fIancil_action\fP\fB);\fP
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| 241 |
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| 242 | \fBvoid png_set_dither (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_dither\fP\fB);\fP
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| 243 |
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| 244 | \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
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| 245 |
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| 246 | \fBvoid png_set_expand (png_structp \fIpng_ptr\fP\fB);\fP
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| 247 |
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| 248 | \fBvoid png_set_expand_gray_1_2_4_to_8(png_structp \fIpng_ptr\fP\fB);\fP
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| 249 |
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| 250 | \fBvoid png_set_filler (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
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| 251 |
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| 252 | \fBvoid png_set_filter (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImethod\fP\fB, int \fIfilters\fP\fB);\fP
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| 253 |
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| 254 | \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
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| 255 |
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| 256 | \fBvoid png_set_flush (png_structp \fP\fIpng_ptr\fP\fB, int \fInrows\fP\fB);\fP
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| 257 |
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| 258 | \fBvoid png_set_gamma (png_structp \fP\fIpng_ptr\fP\fB, double \fP\fIscreen_gamma\fP\fB, double \fIdefault_file_gamma\fP\fB);\fP
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| 259 |
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| 260 | \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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| 261 |
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| 262 | \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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| 263 |
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| 264 | \fBvoid png_set_gray_1_2_4_to_8(png_structp \fIpng_ptr\fP\fB);\fP
|
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| 265 |
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| 266 | \fBvoid png_set_gray_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
|
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| 267 |
|
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| 268 | \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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| 269 |
|
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| 270 | \fBvoid png_set_iCCP (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charp \fP\fIname\fP\fB, int \fP\fIcompression_type\fP\fB, png_charp \fP\fIprofile\fP\fB, png_uint_32 \fIproflen\fP\fB);\fP
|
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| 271 |
|
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| 272 | \fBint png_set_interlace_handling (png_structp \fIpng_ptr\fP\fB);\fP
|
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| 273 |
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| 274 | \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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| 275 |
|
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| 276 | \fBvoid png_set_invert_alpha (png_structp \fIpng_ptr\fP\fB);\fP
|
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| 277 |
|
|---|
| 278 | \fBvoid png_set_invert_mono (png_structp \fIpng_ptr\fP\fB);\fP
|
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| 279 |
|
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| 280 | \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
|
|---|
| 281 |
|
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| 282 | \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
|
|---|
| 283 |
|
|---|
| 284 | \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
|
|---|
| 285 |
|
|---|
| 286 | \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
|
|---|
| 287 |
|
|---|
| 288 | \fBvoid png_set_packing (png_structp \fIpng_ptr\fP\fB);\fP
|
|---|
| 289 |
|
|---|
| 290 | \fBvoid png_set_packswap (png_structp \fIpng_ptr\fP\fB);\fP
|
|---|
| 291 |
|
|---|
| 292 | \fBvoid png_set_palette_to_rgb(png_structp \fIpng_ptr\fP\fB);\fP
|
|---|
| 293 |
|
|---|
| 294 | \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
|
|---|
| 295 |
|
|---|
| 296 | \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
|
|---|
| 297 |
|
|---|
| 298 | \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
|
|---|
| 299 |
|
|---|
| 300 | \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
|
|---|
| 301 |
|
|---|
| 302 | \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
|
|---|
| 303 |
|
|---|
| 304 | \fBvoid png_set_read_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_read_status_ptr \fIread_row_fn\fP\fB);\fP
|
|---|
| 305 |
|
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| 306 | \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
|
|---|
| 307 |
|
|---|
| 308 | \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
|
|---|
| 309 |
|
|---|
| 310 | \fBvoid png_set_rgb_to_gray_fixed (png_structp \fP\fIpng_ptr\fP\fB, int error_action png_fixed_point \fP\fIred\fP\fB, png_fixed_point \fIgreen\fP\fB);\fP
|
|---|
| 311 |
|
|---|
| 312 | \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
|
|---|
| 313 |
|
|---|
| 314 | \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
|
|---|
| 315 |
|
|---|
| 316 | \fBvoid png_set_sCAL (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charp \fP\fIunit\fP\fB, double \fP\fIwidth\fP\fB, double \fIheight\fP\fB);\fP
|
|---|
| 317 |
|
|---|
| 318 | \fBvoid png_set_shift (png_structp \fP\fIpng_ptr\fP\fB, png_color_8p \fItrue_bits\fP\fB);\fP
|
|---|
| 319 |
|
|---|
| 320 | \fBvoid png_set_sig_bytes (png_structp \fP\fIpng_ptr\fP\fB, int \fInum_bytes\fP\fB);\fP
|
|---|
| 321 |
|
|---|
| 322 | \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
|
|---|
| 323 |
|
|---|
| 324 | \fBvoid png_set_sRGB (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIintent\fP\fB);\fP
|
|---|
| 325 |
|
|---|
| 326 | \fBvoid png_set_sRGB_gAMA_and_cHRM (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIintent\fP\fB);\fP
|
|---|
| 327 |
|
|---|
| 328 | \fBvoid png_set_strip_16 (png_structp \fIpng_ptr\fP\fB);\fP
|
|---|
| 329 |
|
|---|
| 330 | \fBvoid png_set_strip_alpha (png_structp \fIpng_ptr\fP\fB);\fP
|
|---|
| 331 |
|
|---|
| 332 | \fBvoid png_set_swap (png_structp \fIpng_ptr\fP\fB);\fP
|
|---|
| 333 |
|
|---|
| 334 | \fBvoid png_set_swap_alpha (png_structp \fIpng_ptr\fP\fB);\fP
|
|---|
| 335 |
|
|---|
| 336 | \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
|
|---|
| 337 |
|
|---|
| 338 | \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
|
|---|
| 339 |
|
|---|
| 340 | \fBvoid png_set_tRNS (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fItrans\fP\fB, int \fP\fInum_trans\fP\fB, png_color_16p \fItrans_values\fP\fB);\fP
|
|---|
| 341 |
|
|---|
| 342 | \fBvoid png_set_tRNS_to_alpha(png_structp \fIpng_ptr\fP\fB);\fP
|
|---|
| 343 |
|
|---|
| 344 | \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
|
|---|
| 345 |
|
|---|
| 346 | \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
|
|---|
| 347 |
|
|---|
| 348 | \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
|
|---|
| 349 |
|
|---|
| 350 | \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
|
|---|
| 351 |
|
|---|
| 352 | \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
|
|---|
| 353 |
|
|---|
| 354 | \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
|
|---|
| 355 |
|
|---|
| 356 | \fBvoid png_set_write_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_write_status_ptr \fIwrite_row_fn\fP\fB);\fP
|
|---|
| 357 |
|
|---|
| 358 | \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
|
|---|
| 359 |
|
|---|
| 360 | \fBvoid png_set_compression_buffer_size(png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
|
|---|
| 361 |
|
|---|
| 362 | \fBint png_sig_cmp (png_bytep \fP\fIsig\fP\fB, png_size_t \fP\fIstart\fP\fB, png_size_t \fInum_to_check\fP\fB);\fP
|
|---|
| 363 |
|
|---|
| 364 | \fBvoid png_start_read_image (png_structp \fIpng_ptr\fP\fB);\fP
|
|---|
| 365 |
|
|---|
| 366 | \fBvoid png_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
|
|---|
| 367 |
|
|---|
| 368 | \fBvoid png_write_chunk (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIchunk_name\fP\fB, png_bytep \fP\fIdata\fP\fB, png_size_t \fIlength\fP\fB);\fP
|
|---|
| 369 |
|
|---|
| 370 | \fBvoid png_write_chunk_data (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIdata\fP\fB, png_size_t \fIlength\fP\fB);\fP
|
|---|
| 371 |
|
|---|
| 372 | \fBvoid png_write_chunk_end (png_structp \fIpng_ptr\fP\fB);\fP
|
|---|
| 373 |
|
|---|
| 374 | \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
|
|---|
| 375 |
|
|---|
| 376 | \fBvoid png_write_destroy (png_structp \fIpng_ptr\fP\fB);\fP
|
|---|
| 377 |
|
|---|
| 378 | \fBvoid png_write_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
|
|---|
| 379 |
|
|---|
| 380 | \fBvoid png_write_flush (png_structp \fIpng_ptr\fP\fB);\fP
|
|---|
| 381 |
|
|---|
| 382 | \fBvoid png_write_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
|
|---|
| 383 |
|
|---|
| 384 | \fBDEPRECATED void png_write_init (png_structp \fIpng_ptr\fP\fB);\fP
|
|---|
| 385 |
|
|---|
| 386 | \fBDEPRECATED void png_write_init_2 (png_structpp \fP\fIptr_ptr\fP\fB, png_const_charp \fP\fIuser_png_ver\fP\fB, png_size_t \fP\fIpng_struct_size\fP\fB, png_size_t \fIpng_info_size\fP\fB);\fP
|
|---|
| 387 |
|
|---|
| 388 | \fBvoid png_write_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
|
|---|
| 389 |
|
|---|
| 390 | \fBvoid png_write_info_before_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
|
|---|
| 391 |
|
|---|
| 392 | \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
|
|---|
| 393 |
|
|---|
| 394 | \fBvoid png_write_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIrow\fP\fB);\fP
|
|---|
| 395 |
|
|---|
| 396 | \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
|
|---|
| 397 |
|
|---|
| 398 | \fBvoidpf png_zalloc (voidpf \fP\fIpng_ptr\fP\fB, uInt \fP\fIitems\fP\fB, uInt \fIsize\fP\fB);\fP
|
|---|
| 399 |
|
|---|
| 400 | \fBvoid png_zfree (voidpf \fP\fIpng_ptr\fP\fB, voidpf \fIptr\fP\fB);\fP
|
|---|
| 401 |
|
|---|
| 402 | .SH DESCRIPTION
|
|---|
| 403 | The
|
|---|
| 404 | .I libpng
|
|---|
| 405 | library supports encoding, decoding, and various manipulations of
|
|---|
| 406 | the Portable Network Graphics (PNG) format image files. It uses the
|
|---|
| 407 | .IR zlib(3)
|
|---|
| 408 | compression library.
|
|---|
| 409 | Following is a copy of the libpng.txt file that accompanies libpng.
|
|---|
| 410 | .SH LIBPNG.TXT
|
|---|
| 411 | libpng.txt - A description on how to use and modify libpng
|
|---|
| 412 |
|
|---|
| 413 | libpng version 1.2.54 - November 12, 2015
|
|---|
| 414 | Updated and distributed by Glenn Randers-Pehrson
|
|---|
| 415 | <glennrp at users.sourceforge.net>
|
|---|
| 416 | Copyright (c) 1998-2014 Glenn Randers-Pehrson
|
|---|
| 417 |
|
|---|
| 418 | This document is released under the libpng license.
|
|---|
| 419 | For conditions of distribution and use, see the disclaimer
|
|---|
| 420 | and license in png.h
|
|---|
| 421 |
|
|---|
| 422 | Based on:
|
|---|
| 423 |
|
|---|
| 424 | libpng versions 0.97, January 1998, through 1.2.54 - November 12, 2015
|
|---|
| 425 | Updated and distributed by Glenn Randers-Pehrson
|
|---|
| 426 | Copyright (c) 1998-2014 Glenn Randers-Pehrson
|
|---|
| 427 |
|
|---|
| 428 | libpng 1.0 beta 6 version 0.96 May 28, 1997
|
|---|
| 429 | Updated and distributed by Andreas Dilger
|
|---|
| 430 | Copyright (c) 1996, 1997 Andreas Dilger
|
|---|
| 431 |
|
|---|
| 432 | libpng 1.0 beta 2 - version 0.88 January 26, 1996
|
|---|
| 433 | For conditions of distribution and use, see copyright
|
|---|
| 434 | notice in png.h. Copyright (c) 1995, 1996 Guy Eric
|
|---|
| 435 | Schalnat, Group 42, Inc.
|
|---|
| 436 |
|
|---|
| 437 | Updated/rewritten per request in the libpng FAQ
|
|---|
| 438 | Copyright (c) 1995, 1996 Frank J. T. Wojcik
|
|---|
| 439 | December 18, 1995 & January 20, 1996
|
|---|
| 440 |
|
|---|
| 441 | .SH I. Introduction
|
|---|
| 442 |
|
|---|
| 443 | This file describes how to use and modify the PNG reference library
|
|---|
| 444 | (known as libpng) for your own use. There are five sections to this
|
|---|
| 445 | file: introduction, structures, reading, writing, and modification and
|
|---|
| 446 | configuration notes for various special platforms. In addition to this
|
|---|
| 447 | file, example.c is a good starting point for using the library, as
|
|---|
| 448 | it is heavily commented and should include everything most people
|
|---|
| 449 | will need. We assume that libpng is already installed; see the
|
|---|
| 450 | INSTALL file for instructions on how to install libpng.
|
|---|
| 451 |
|
|---|
| 452 | For examples of libpng usage, see the files "example.c", "pngtest.c",
|
|---|
| 453 | and the files in the "contrib" directory, all of which are included in
|
|---|
| 454 | the libpng distribution.
|
|---|
| 455 |
|
|---|
| 456 | Libpng was written as a companion to the PNG specification, as a way
|
|---|
| 457 | of reducing the amount of time and effort it takes to support the PNG
|
|---|
| 458 | file format in application programs.
|
|---|
| 459 |
|
|---|
| 460 | The PNG specification (second edition), November 2003, is available as
|
|---|
| 461 | a W3C Recommendation and as an ISO Standard (ISO/IEC 15948:2003 (E)) at
|
|---|
| 462 | <http://www.w3.org/TR/2003/REC-PNG-20031110/
|
|---|
| 463 | The W3C and ISO documents have identical technical content.
|
|---|
| 464 |
|
|---|
| 465 | The PNG-1.2 specification is available at
|
|---|
| 466 | <http://png-mng.sourceforge.net/pub/png/spec/1.2/>.
|
|---|
| 467 | It is technically equivalent
|
|---|
| 468 | to the PNG specification (second edition) but has some additional material.
|
|---|
| 469 |
|
|---|
| 470 | The PNG-1.0 specification is available as RFC 2083
|
|---|
| 471 | <http://png-mng.sourceforge.net/pub/png/spec/1.0/> and as a
|
|---|
| 472 | W3C Recommendation <http://www.w3.org/TR/REC-png-961001>.
|
|---|
| 473 |
|
|---|
| 474 | Some additional chunks are described in the special-purpose public chunks
|
|---|
| 475 | documents at <http://www.libpng.org/pub/png/spec/register/>
|
|---|
| 476 |
|
|---|
| 477 | Other information
|
|---|
| 478 | about PNG, and the latest version of libpng, can be found at the PNG home
|
|---|
| 479 | page, <http://www.libpng.org/pub/png/>.
|
|---|
| 480 |
|
|---|
| 481 | Most users will not have to modify the library significantly; advanced
|
|---|
| 482 | users may want to modify it more. All attempts were made to make it as
|
|---|
| 483 | complete as possible, while keeping the code easy to understand.
|
|---|
| 484 | Currently, this library only supports C. Support for other languages
|
|---|
| 485 | is being considered.
|
|---|
| 486 |
|
|---|
| 487 | Libpng has been designed to handle multiple sessions at one time,
|
|---|
| 488 | to be easily modifiable, to be portable to the vast majority of
|
|---|
| 489 | machines (ANSI, K&R, 16-, 32-, and 64-bit) available, and to be easy
|
|---|
| 490 | to use. The ultimate goal of libpng is to promote the acceptance of
|
|---|
| 491 | the PNG file format in whatever way possible. While there is still
|
|---|
| 492 | work to be done (see the TODO file), libpng should cover the
|
|---|
| 493 | majority of the needs of its users.
|
|---|
| 494 |
|
|---|
| 495 | Libpng uses zlib for its compression and decompression of PNG files.
|
|---|
| 496 | Further information about zlib, and the latest version of zlib, can
|
|---|
| 497 | be found at the zlib home page, <http://zlib.net/>.
|
|---|
| 498 | The zlib compression utility is a general purpose utility that is
|
|---|
| 499 | useful for more than PNG files, and can be used without libpng.
|
|---|
| 500 | See the documentation delivered with zlib for more details.
|
|---|
| 501 | You can usually find the source files for the zlib utility wherever you
|
|---|
| 502 | find the libpng source files.
|
|---|
| 503 |
|
|---|
| 504 | Libpng is thread safe, provided the threads are using different
|
|---|
| 505 | instances of the structures. Each thread should have its own
|
|---|
| 506 | png_struct and png_info instances, and thus its own image.
|
|---|
| 507 | Libpng does not protect itself against two threads using the
|
|---|
| 508 | same instance of a structure.
|
|---|
| 509 |
|
|---|
| 510 | .SH II. Structures
|
|---|
| 511 |
|
|---|
| 512 | There are two main structures that are important to libpng, png_struct
|
|---|
| 513 | and png_info. The first, png_struct, is an internal structure that
|
|---|
| 514 | will not, for the most part, be used by a user except as the first
|
|---|
| 515 | variable passed to every libpng function call.
|
|---|
| 516 |
|
|---|
| 517 | The png_info structure is designed to provide information about the
|
|---|
| 518 | PNG file. At one time, the fields of png_info were intended to be
|
|---|
| 519 | directly accessible to the user. However, this tended to cause problems
|
|---|
| 520 | with applications using dynamically loaded libraries, and as a result
|
|---|
| 521 | a set of interface functions for png_info (the png_get_*() and png_set_*()
|
|---|
| 522 | functions) was developed. The fields of png_info are still available for
|
|---|
| 523 | older applications, but it is suggested that applications use the new
|
|---|
| 524 | interfaces if at all possible.
|
|---|
| 525 |
|
|---|
| 526 | Applications that do make direct access to the members of png_struct (except
|
|---|
| 527 | for png_ptr->jmpbuf) must be recompiled whenever the library is updated,
|
|---|
| 528 | and applications that make direct access to the members of png_info must
|
|---|
| 529 | be recompiled if they were compiled or loaded with libpng version 1.0.6,
|
|---|
| 530 | in which the members were in a different order. In version 1.0.7, the
|
|---|
| 531 | members of the png_info structure reverted to the old order, as they were
|
|---|
| 532 | in versions 0.97c through 1.0.5. Starting with version 2.0.0, both
|
|---|
| 533 | structures are going to be hidden, and the contents of the structures will
|
|---|
| 534 | only be accessible through the png_get/png_set functions.
|
|---|
| 535 |
|
|---|
| 536 | The png.h header file is an invaluable reference for programming with libpng.
|
|---|
| 537 | And while I'm on the topic, make sure you include the libpng header file:
|
|---|
| 538 |
|
|---|
| 539 | #include <png.h>
|
|---|
| 540 |
|
|---|
| 541 | .SH III. Reading
|
|---|
| 542 |
|
|---|
| 543 | We'll now walk you through the possible functions to call when reading
|
|---|
| 544 | in a PNG file sequentially, briefly explaining the syntax and purpose
|
|---|
| 545 | of each one. See example.c and png.h for more detail. While
|
|---|
| 546 | progressive reading is covered in the next section, you will still
|
|---|
| 547 | need some of the functions discussed in this section to read a PNG
|
|---|
| 548 | file.
|
|---|
| 549 |
|
|---|
| 550 | .SS Setup
|
|---|
| 551 |
|
|---|
| 552 | You will want to do the I/O initialization(*) before you get into libpng,
|
|---|
| 553 | so if it doesn't work, you don't have much to undo. Of course, you
|
|---|
| 554 | will also want to insure that you are, in fact, dealing with a PNG
|
|---|
| 555 | file. Libpng provides a simple check to see if a file is a PNG file.
|
|---|
| 556 | To use it, pass in the first 1 to 8 bytes of the file to the function
|
|---|
| 557 | png_sig_cmp(), and it will return 0 (false) if the bytes match the
|
|---|
| 558 | corresponding bytes of the PNG signature, or nonzero (true) otherwise.
|
|---|
| 559 | Of course, the more bytes you pass in, the greater the accuracy of the
|
|---|
| 560 | prediction.
|
|---|
| 561 |
|
|---|
| 562 | If you are intending to keep the file pointer open for use in libpng,
|
|---|
| 563 | you must ensure you don't read more than 8 bytes from the beginning
|
|---|
| 564 | of the file, and you also have to make a call to png_set_sig_bytes()
|
|---|
| 565 | with the number of bytes you read from the beginning. Libpng will
|
|---|
| 566 | then only check the bytes (if any) that your program didn't read.
|
|---|
| 567 |
|
|---|
| 568 | (*): If you are not using the standard I/O functions, you will need
|
|---|
| 569 | to replace them with custom functions. See the discussion under
|
|---|
| 570 | Customizing libpng.
|
|---|
| 571 |
|
|---|
| 572 |
|
|---|
| 573 | FILE *fp = fopen(file_name, "rb");
|
|---|
| 574 | if (!fp)
|
|---|
| 575 | {
|
|---|
| 576 | return (ERROR);
|
|---|
| 577 | }
|
|---|
| 578 | fread(header, 1, number, fp);
|
|---|
| 579 | is_png = !png_sig_cmp(header, 0, number);
|
|---|
| 580 | if (!is_png)
|
|---|
| 581 | {
|
|---|
| 582 | return (NOT_PNG);
|
|---|
| 583 | }
|
|---|
| 584 |
|
|---|
| 585 |
|
|---|
| 586 | Next, png_struct and png_info need to be allocated and initialized. In
|
|---|
| 587 | order to ensure that the size of these structures is correct even with a
|
|---|
| 588 | dynamically linked libpng, there are functions to initialize and
|
|---|
| 589 | allocate the structures. We also pass the library version, optional
|
|---|
| 590 | pointers to error handling functions, and a pointer to a data struct for
|
|---|
| 591 | use by the error functions, if necessary (the pointer and functions can
|
|---|
| 592 | be NULL if the default error handlers are to be used). See the section
|
|---|
| 593 | on Changes to Libpng below regarding the old initialization functions.
|
|---|
| 594 | The structure allocation functions quietly return NULL if they fail to
|
|---|
| 595 | create the structure, so your application should check for that.
|
|---|
| 596 |
|
|---|
| 597 | png_structp png_ptr = png_create_read_struct
|
|---|
| 598 | (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
|
|---|
| 599 | user_error_fn, user_warning_fn);
|
|---|
| 600 | if (!png_ptr)
|
|---|
| 601 | return (ERROR);
|
|---|
| 602 |
|
|---|
| 603 | png_infop info_ptr = png_create_info_struct(png_ptr);
|
|---|
| 604 | if (!info_ptr)
|
|---|
| 605 | {
|
|---|
| 606 | png_destroy_read_struct(&png_ptr,
|
|---|
| 607 | (png_infopp)NULL, (png_infopp)NULL);
|
|---|
| 608 | return (ERROR);
|
|---|
| 609 | }
|
|---|
| 610 |
|
|---|
| 611 | png_infop end_info = png_create_info_struct(png_ptr);
|
|---|
| 612 | if (!end_info)
|
|---|
| 613 | {
|
|---|
| 614 | png_destroy_read_struct(&png_ptr, &info_ptr,
|
|---|
| 615 | (png_infopp)NULL);
|
|---|
| 616 | return (ERROR);
|
|---|
| 617 | }
|
|---|
| 618 |
|
|---|
| 619 | If you want to use your own memory allocation routines,
|
|---|
| 620 | define PNG_USER_MEM_SUPPORTED and use
|
|---|
| 621 | png_create_read_struct_2() instead of png_create_read_struct():
|
|---|
| 622 |
|
|---|
| 623 | png_structp png_ptr = png_create_read_struct_2
|
|---|
| 624 | (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
|
|---|
| 625 | user_error_fn, user_warning_fn, (png_voidp)
|
|---|
| 626 | user_mem_ptr, user_malloc_fn, user_free_fn);
|
|---|
| 627 |
|
|---|
| 628 | The error handling routines passed to png_create_read_struct()
|
|---|
| 629 | and the memory alloc/free routines passed to png_create_struct_2()
|
|---|
| 630 | are only necessary if you are not using the libpng supplied error
|
|---|
| 631 | handling and memory alloc/free functions.
|
|---|
| 632 |
|
|---|
| 633 | When libpng encounters an error, it expects to longjmp back
|
|---|
| 634 | to your routine. Therefore, you will need to call setjmp and pass
|
|---|
| 635 | your png_jmpbuf(png_ptr). If you read the file from different
|
|---|
| 636 | routines, you will need to update the jmpbuf field every time you enter
|
|---|
| 637 | a new routine that will call a png_*() function.
|
|---|
| 638 |
|
|---|
| 639 | See your documentation of setjmp/longjmp for your compiler for more
|
|---|
| 640 | information on setjmp/longjmp. See the discussion on libpng error
|
|---|
| 641 | handling in the Customizing Libpng section below for more information
|
|---|
| 642 | on the libpng error handling. If an error occurs, and libpng longjmp's
|
|---|
| 643 | back to your setjmp, you will want to call png_destroy_read_struct() to
|
|---|
| 644 | free any memory.
|
|---|
| 645 |
|
|---|
| 646 | if (setjmp(png_jmpbuf(png_ptr)))
|
|---|
| 647 | {
|
|---|
| 648 | png_destroy_read_struct(&png_ptr, &info_ptr,
|
|---|
| 649 | &end_info);
|
|---|
| 650 | fclose(fp);
|
|---|
| 651 | return (ERROR);
|
|---|
| 652 | }
|
|---|
| 653 |
|
|---|
| 654 | If you would rather avoid the complexity of setjmp/longjmp issues,
|
|---|
| 655 | you can compile libpng with PNG_SETJMP_NOT_SUPPORTED, in which case
|
|---|
| 656 | errors will result in a call to PNG_ABORT() which defaults to abort().
|
|---|
| 657 |
|
|---|
| 658 | Now you need to set up the input code. The default for libpng is to
|
|---|
| 659 | use the C function fread(). If you use this, you will need to pass a
|
|---|
| 660 | valid FILE * in the function png_init_io(). Be sure that the file is
|
|---|
| 661 | opened in binary mode. If you wish to handle reading data in another
|
|---|
| 662 | way, you need not call the png_init_io() function, but you must then
|
|---|
| 663 | implement the libpng I/O methods discussed in the Customizing Libpng
|
|---|
| 664 | section below.
|
|---|
| 665 |
|
|---|
| 666 | png_init_io(png_ptr, fp);
|
|---|
| 667 |
|
|---|
| 668 | If you had previously opened the file and read any of the signature from
|
|---|
| 669 | the beginning in order to see if this was a PNG file, you need to let
|
|---|
| 670 | libpng know that there are some bytes missing from the start of the file.
|
|---|
| 671 |
|
|---|
| 672 | png_set_sig_bytes(png_ptr, number);
|
|---|
| 673 |
|
|---|
| 674 | .SS Setting up callback code
|
|---|
| 675 |
|
|---|
| 676 | You can set up a callback function to handle any unknown chunks in the
|
|---|
| 677 | input stream. You must supply the function
|
|---|
| 678 |
|
|---|
| 679 | read_chunk_callback(png_ptr ptr,
|
|---|
| 680 | png_unknown_chunkp chunk);
|
|---|
| 681 | {
|
|---|
| 682 | /* The unknown chunk structure contains your
|
|---|
| 683 | chunk data, along with similar data for any other
|
|---|
| 684 | unknown chunks: */
|
|---|
| 685 |
|
|---|
| 686 | png_byte name[5];
|
|---|
| 687 | png_byte *data;
|
|---|
| 688 | png_size_t size;
|
|---|
| 689 |
|
|---|
| 690 | /* Note that libpng has already taken care of
|
|---|
| 691 | the CRC handling */
|
|---|
| 692 |
|
|---|
| 693 | /* put your code here. Search for your chunk in the
|
|---|
| 694 | unknown chunk structure, process it, and return one
|
|---|
| 695 | of the following: */
|
|---|
| 696 |
|
|---|
| 697 | return (\-n); /* chunk had an error */
|
|---|
| 698 | return (0); /* did not recognize */
|
|---|
| 699 | return (n); /* success */
|
|---|
| 700 | }
|
|---|
| 701 |
|
|---|
| 702 | (You can give your function another name that you like instead of
|
|---|
| 703 | "read_chunk_callback")
|
|---|
| 704 |
|
|---|
| 705 | To inform libpng about your function, use
|
|---|
| 706 |
|
|---|
| 707 | png_set_read_user_chunk_fn(png_ptr, user_chunk_ptr,
|
|---|
| 708 | read_chunk_callback);
|
|---|
| 709 |
|
|---|
| 710 | This names not only the callback function, but also a user pointer that
|
|---|
| 711 | you can retrieve with
|
|---|
| 712 |
|
|---|
| 713 | png_get_user_chunk_ptr(png_ptr);
|
|---|
| 714 |
|
|---|
| 715 | If you call the png_set_read_user_chunk_fn() function, then all unknown
|
|---|
| 716 | chunks will be saved when read, in case your callback function will need
|
|---|
| 717 | one or more of them. This behavior can be changed with the
|
|---|
| 718 | png_set_keep_unknown_chunks() function, described below.
|
|---|
| 719 |
|
|---|
| 720 | At this point, you can set up a callback function that will be
|
|---|
| 721 | called after each row has been read, which you can use to control
|
|---|
| 722 | a progress meter or the like. It's demonstrated in pngtest.c.
|
|---|
| 723 | You must supply a function
|
|---|
| 724 |
|
|---|
| 725 | void read_row_callback(png_ptr ptr, png_uint_32 row,
|
|---|
| 726 | int pass);
|
|---|
| 727 | {
|
|---|
| 728 | /* put your code here */
|
|---|
| 729 | }
|
|---|
| 730 |
|
|---|
| 731 | (You can give it another name that you like instead of "read_row_callback")
|
|---|
| 732 |
|
|---|
| 733 | To inform libpng about your function, use
|
|---|
| 734 |
|
|---|
| 735 | png_set_read_status_fn(png_ptr, read_row_callback);
|
|---|
| 736 |
|
|---|
| 737 | .SS Unknown-chunk handling
|
|---|
| 738 |
|
|---|
| 739 | Now you get to set the way the library processes unknown chunks in the
|
|---|
| 740 | input PNG stream. Both known and unknown chunks will be read. Normal
|
|---|
| 741 | behavior is that known chunks will be parsed into information in
|
|---|
| 742 | various info_ptr members while unknown chunks will be discarded. This
|
|---|
| 743 | behavior can be wasteful if your application will never use some known
|
|---|
| 744 | chunk types. To change this, you can call:
|
|---|
| 745 |
|
|---|
| 746 | png_set_keep_unknown_chunks(png_ptr, keep,
|
|---|
| 747 | chunk_list, num_chunks);
|
|---|
| 748 | keep - 0: default unknown chunk handling
|
|---|
| 749 | 1: ignore; do not keep
|
|---|
| 750 | 2: keep only if safe-to-copy
|
|---|
| 751 | 3: keep even if unsafe-to-copy
|
|---|
| 752 | You can use these definitions:
|
|---|
| 753 | PNG_HANDLE_CHUNK_AS_DEFAULT 0
|
|---|
| 754 | PNG_HANDLE_CHUNK_NEVER 1
|
|---|
| 755 | PNG_HANDLE_CHUNK_IF_SAFE 2
|
|---|
| 756 | PNG_HANDLE_CHUNK_ALWAYS 3
|
|---|
| 757 | chunk_list - list of chunks affected (a byte string,
|
|---|
| 758 | five bytes per chunk, NULL or '\0' if
|
|---|
| 759 | num_chunks is 0)
|
|---|
| 760 | num_chunks - number of chunks affected; if 0, all
|
|---|
| 761 | unknown chunks are affected. If nonzero,
|
|---|
| 762 | only the chunks in the list are affected
|
|---|
| 763 |
|
|---|
| 764 | Unknown chunks declared in this way will be saved as raw data onto a
|
|---|
| 765 | list of png_unknown_chunk structures. If a chunk that is normally
|
|---|
| 766 | known to libpng is named in the list, it will be handled as unknown,
|
|---|
| 767 | according to the "keep" directive. If a chunk is named in successive
|
|---|
| 768 | instances of png_set_keep_unknown_chunks(), the final instance will
|
|---|
| 769 | take precedence. The IHDR and IEND chunks should not be named in
|
|---|
| 770 | chunk_list; if they are, libpng will process them normally anyway.
|
|---|
| 771 |
|
|---|
| 772 | Here is an example of the usage of png_set_keep_unknown_chunks(),
|
|---|
| 773 | where the private "vpAg" chunk will later be processed by a user chunk
|
|---|
| 774 | callback function:
|
|---|
| 775 |
|
|---|
| 776 | png_byte vpAg[5]={118, 112, 65, 103, (png_byte) '\0'};
|
|---|
| 777 |
|
|---|
| 778 | #if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
|
|---|
| 779 | png_byte unused_chunks[]=
|
|---|
| 780 | {
|
|---|
| 781 | 104, 73, 83, 84, (png_byte) '\0', /* hIST */
|
|---|
| 782 | 105, 84, 88, 116, (png_byte) '\0', /* iTXt */
|
|---|
| 783 | 112, 67, 65, 76, (png_byte) '\0', /* pCAL */
|
|---|
| 784 | 115, 67, 65, 76, (png_byte) '\0', /* sCAL */
|
|---|
| 785 | 115, 80, 76, 84, (png_byte) '\0', /* sPLT */
|
|---|
| 786 | 116, 73, 77, 69, (png_byte) '\0', /* tIME */
|
|---|
| 787 | };
|
|---|
| 788 | #endif
|
|---|
| 789 |
|
|---|
| 790 | ...
|
|---|
| 791 |
|
|---|
| 792 | #if defined(PNG_UNKNOWN_CHUNKS_SUPPORTED)
|
|---|
| 793 | /* ignore all unknown chunks: */
|
|---|
| 794 | png_set_keep_unknown_chunks(read_ptr, 1, NULL, 0);
|
|---|
| 795 | /* except for vpAg: */
|
|---|
| 796 | png_set_keep_unknown_chunks(read_ptr, 2, vpAg, 1);
|
|---|
| 797 | /* also ignore unused known chunks: */
|
|---|
| 798 | png_set_keep_unknown_chunks(read_ptr, 1, unused_chunks,
|
|---|
| 799 | (int)sizeof(unused_chunks)/5);
|
|---|
| 800 | #endif
|
|---|
| 801 |
|
|---|
| 802 | .SS User limits
|
|---|
| 803 |
|
|---|
| 804 | The PNG specification allows the width and height of an image to be as
|
|---|
| 805 | large as 2^(31\-1 (0x7fffffff), or about 2.147 billion rows and columns.
|
|---|
| 806 | Since very few applications really need to process such large images,
|
|---|
| 807 | we have imposed an arbitrary 1-million limit on rows and columns.
|
|---|
| 808 | Larger images will be rejected immediately with a png_error() call. If
|
|---|
| 809 | you wish to override this limit, you can use
|
|---|
| 810 |
|
|---|
| 811 | png_set_user_limits(png_ptr, width_max, height_max);
|
|---|
| 812 |
|
|---|
| 813 | to set your own limits, or use width_max = height_max = 0x7fffffffL
|
|---|
| 814 | to allow all valid dimensions (libpng may reject some very large images
|
|---|
| 815 | anyway because of potential buffer overflow conditions).
|
|---|
| 816 |
|
|---|
| 817 | You should put this statement after you create the PNG structure and
|
|---|
| 818 | before calling png_read_info(), png_read_png(), or png_process_data().
|
|---|
| 819 | If you need to retrieve the limits that are being applied, use
|
|---|
| 820 |
|
|---|
| 821 | width_max = png_get_user_width_max(png_ptr);
|
|---|
| 822 | height_max = png_get_user_height_max(png_ptr);
|
|---|
| 823 |
|
|---|
| 824 | The PNG specification sets no limit on the number of ancillary chunks
|
|---|
| 825 | allowed in a PNG datastream. You can impose a limit on the total number
|
|---|
| 826 | of sPLT, tEXt, iTXt, zTXt, and unknown chunks that will be stored, with
|
|---|
| 827 |
|
|---|
| 828 | png_set_chunk_cache_max(png_ptr, user_chunk_cache_max);
|
|---|
| 829 |
|
|---|
| 830 | where 0x7fffffffL means unlimited. You can retrieve this limit with
|
|---|
| 831 |
|
|---|
| 832 | chunk_cache_max = png_get_chunk_cache_max(png_ptr);
|
|---|
| 833 |
|
|---|
| 834 | This limit also applies to the number of buffers that can be allocated
|
|---|
| 835 | by png_decompress_chunk() while decompressing iTXt, zTXt, and iCCP chunks.
|
|---|
| 836 |
|
|---|
| 837 | .SS The high-level read interface
|
|---|
| 838 |
|
|---|
| 839 | At this point there are two ways to proceed; through the high-level
|
|---|
| 840 | read interface, or through a sequence of low-level read operations.
|
|---|
| 841 | You can use the high-level interface if (a) you are willing to read
|
|---|
| 842 | the entire image into memory, and (b) the input transformations
|
|---|
| 843 | you want to do are limited to the following set:
|
|---|
| 844 |
|
|---|
| 845 | PNG_TRANSFORM_IDENTITY No transformation
|
|---|
| 846 | PNG_TRANSFORM_STRIP_16 Strip 16-bit samples to
|
|---|
| 847 | 8 bits
|
|---|
| 848 | PNG_TRANSFORM_STRIP_ALPHA Discard the alpha channel
|
|---|
| 849 | PNG_TRANSFORM_PACKING Expand 1, 2 and 4-bit
|
|---|
| 850 | samples to bytes
|
|---|
| 851 | PNG_TRANSFORM_PACKSWAP Change order of packed
|
|---|
| 852 | pixels to LSB first
|
|---|
| 853 | PNG_TRANSFORM_EXPAND Perform set_expand()
|
|---|
| 854 | PNG_TRANSFORM_INVERT_MONO Invert monochrome images
|
|---|
| 855 | PNG_TRANSFORM_SHIFT Normalize pixels to the
|
|---|
| 856 | sBIT depth
|
|---|
| 857 | PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
|
|---|
| 858 | to BGRA
|
|---|
| 859 | PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
|
|---|
| 860 | to AG
|
|---|
| 861 | PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
|
|---|
| 862 | to transparency
|
|---|
| 863 | PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
|
|---|
| 864 | PNG_TRANSFORM_GRAY_TO_RGB Expand grayscale samples
|
|---|
| 865 | to RGB (or GA to RGBA)
|
|---|
| 866 |
|
|---|
| 867 | (This excludes setting a background color, doing gamma transformation,
|
|---|
| 868 | dithering, and setting filler.) If this is the case, simply do this:
|
|---|
| 869 |
|
|---|
| 870 | png_read_png(png_ptr, info_ptr, png_transforms, NULL)
|
|---|
| 871 |
|
|---|
| 872 | where png_transforms is an integer containing the bitwise OR of some
|
|---|
| 873 | set of transformation flags. This call is equivalent to png_read_info(),
|
|---|
| 874 | followed the set of transformations indicated by the transform mask,
|
|---|
| 875 | then png_read_image(), and finally png_read_end().
|
|---|
| 876 |
|
|---|
| 877 | (The final parameter of this call is not yet used. Someday it might point
|
|---|
| 878 | to transformation parameters required by some future input transform.)
|
|---|
| 879 |
|
|---|
| 880 | You must use png_transforms and not call any png_set_transform() functions
|
|---|
| 881 | when you use png_read_png().
|
|---|
| 882 |
|
|---|
| 883 | After you have called png_read_png(), you can retrieve the image data
|
|---|
| 884 | with
|
|---|
| 885 |
|
|---|
| 886 | row_pointers = png_get_rows(png_ptr, info_ptr);
|
|---|
| 887 |
|
|---|
| 888 | where row_pointers is an array of pointers to the pixel data for each row:
|
|---|
| 889 |
|
|---|
| 890 | png_bytep row_pointers[height];
|
|---|
| 891 |
|
|---|
| 892 | If you know your image size and pixel size ahead of time, you can allocate
|
|---|
| 893 | row_pointers prior to calling png_read_png() with
|
|---|
| 894 |
|
|---|
| 895 | if (height > PNG_UINT_32_MAX/png_sizeof(png_byte))
|
|---|
| 896 | png_error (png_ptr,
|
|---|
| 897 | "Image is too tall to process in memory");
|
|---|
| 898 | if (width > PNG_UINT_32_MAX/pixel_size)
|
|---|
| 899 | png_error (png_ptr,
|
|---|
| 900 | "Image is too wide to process in memory");
|
|---|
| 901 | row_pointers = png_malloc(png_ptr,
|
|---|
| 902 | height*png_sizeof(png_bytep));
|
|---|
| 903 | for (int i=0; i<height, i++)
|
|---|
| 904 | row_pointers[i]=NULL; /* security precaution */
|
|---|
| 905 | for (int i=0; i<height, i++)
|
|---|
| 906 | row_pointers[i]=png_malloc(png_ptr,
|
|---|
| 907 | width*pixel_size);
|
|---|
| 908 | png_set_rows(png_ptr, info_ptr, &row_pointers);
|
|---|
| 909 |
|
|---|
| 910 | Alternatively you could allocate your image in one big block and define
|
|---|
| 911 | row_pointers[i] to point into the proper places in your block.
|
|---|
| 912 |
|
|---|
| 913 | If you use png_set_rows(), the application is responsible for freeing
|
|---|
| 914 | row_pointers (and row_pointers[i], if they were separately allocated).
|
|---|
| 915 |
|
|---|
| 916 | If you don't allocate row_pointers ahead of time, png_read_png() will
|
|---|
| 917 | do it, and it'll be free'ed when you call png_destroy_*().
|
|---|
| 918 |
|
|---|
| 919 | .SS The low-level read interface
|
|---|
| 920 |
|
|---|
| 921 | If you are going the low-level route, you are now ready to read all
|
|---|
| 922 | the file information up to the actual image data. You do this with a
|
|---|
| 923 | call to png_read_info().
|
|---|
| 924 |
|
|---|
| 925 | png_read_info(png_ptr, info_ptr);
|
|---|
| 926 |
|
|---|
| 927 | This will process all chunks up to but not including the image data.
|
|---|
| 928 |
|
|---|
| 929 | .SS Querying the info structure
|
|---|
| 930 |
|
|---|
| 931 | Functions are used to get the information from the info_ptr once it
|
|---|
| 932 | has been read. Note that these fields may not be completely filled
|
|---|
| 933 | in until png_read_end() has read the chunk data following the image.
|
|---|
| 934 |
|
|---|
| 935 | png_get_IHDR(png_ptr, info_ptr, &width, &height,
|
|---|
| 936 | &bit_depth, &color_type, &interlace_type,
|
|---|
| 937 | &compression_type, &filter_method);
|
|---|
| 938 |
|
|---|
| 939 | width - holds the width of the image
|
|---|
| 940 | in pixels (up to 2^31).
|
|---|
| 941 | height - holds the height of the image
|
|---|
| 942 | in pixels (up to 2^31).
|
|---|
| 943 | bit_depth - holds the bit depth of one of the
|
|---|
| 944 | image channels. (valid values are
|
|---|
| 945 | 1, 2, 4, 8, 16 and depend also on
|
|---|
| 946 | the color_type. See also
|
|---|
| 947 | significant bits (sBIT) below).
|
|---|
| 948 | color_type - describes which color/alpha channels
|
|---|
| 949 | are present.
|
|---|
| 950 | PNG_COLOR_TYPE_GRAY
|
|---|
| 951 | (bit depths 1, 2, 4, 8, 16)
|
|---|
| 952 | PNG_COLOR_TYPE_GRAY_ALPHA
|
|---|
| 953 | (bit depths 8, 16)
|
|---|
| 954 | PNG_COLOR_TYPE_PALETTE
|
|---|
| 955 | (bit depths 1, 2, 4, 8)
|
|---|
| 956 | PNG_COLOR_TYPE_RGB
|
|---|
| 957 | (bit_depths 8, 16)
|
|---|
| 958 | PNG_COLOR_TYPE_RGB_ALPHA
|
|---|
| 959 | (bit_depths 8, 16)
|
|---|
| 960 |
|
|---|
| 961 | PNG_COLOR_MASK_PALETTE
|
|---|
| 962 | PNG_COLOR_MASK_COLOR
|
|---|
| 963 | PNG_COLOR_MASK_ALPHA
|
|---|
| 964 |
|
|---|
| 965 | filter_method - (must be PNG_FILTER_TYPE_BASE
|
|---|
| 966 | for PNG 1.0, and can also be
|
|---|
| 967 | PNG_INTRAPIXEL_DIFFERENCING if
|
|---|
| 968 | the PNG datastream is embedded in
|
|---|
| 969 | a MNG-1.0 datastream)
|
|---|
| 970 | compression_type - (must be PNG_COMPRESSION_TYPE_BASE
|
|---|
| 971 | for PNG 1.0)
|
|---|
| 972 | interlace_type - (PNG_INTERLACE_NONE or
|
|---|
| 973 | PNG_INTERLACE_ADAM7)
|
|---|
| 974 |
|
|---|
| 975 | Any or all of interlace_type, compression_type, or
|
|---|
| 976 | filter_method can be NULL if you are
|
|---|
| 977 | not interested in their values.
|
|---|
| 978 |
|
|---|
| 979 | Note that png_get_IHDR() returns 32-bit data into
|
|---|
| 980 | the application's width and height variables.
|
|---|
| 981 | This is an unsafe situation if these are 16-bit
|
|---|
| 982 | variables. In such situations, the
|
|---|
| 983 | png_get_image_width() and png_get_image_height()
|
|---|
| 984 | functions described below are safer.
|
|---|
| 985 |
|
|---|
| 986 | width = png_get_image_width(png_ptr,
|
|---|
| 987 | info_ptr);
|
|---|
| 988 | height = png_get_image_height(png_ptr,
|
|---|
| 989 | info_ptr);
|
|---|
| 990 | bit_depth = png_get_bit_depth(png_ptr,
|
|---|
| 991 | info_ptr);
|
|---|
| 992 | color_type = png_get_color_type(png_ptr,
|
|---|
| 993 | info_ptr);
|
|---|
| 994 | filter_method = png_get_filter_type(png_ptr,
|
|---|
| 995 | info_ptr);
|
|---|
| 996 | compression_type = png_get_compression_type(png_ptr,
|
|---|
| 997 | info_ptr);
|
|---|
| 998 | interlace_type = png_get_interlace_type(png_ptr,
|
|---|
| 999 | info_ptr);
|
|---|
| 1000 |
|
|---|
| 1001 | channels = png_get_channels(png_ptr, info_ptr);
|
|---|
| 1002 | channels - number of channels of info for the
|
|---|
| 1003 | color type (valid values are 1 (GRAY,
|
|---|
| 1004 | PALETTE), 2 (GRAY_ALPHA), 3 (RGB),
|
|---|
| 1005 | 4 (RGB_ALPHA or RGB + filler byte))
|
|---|
| 1006 | rowbytes = png_get_rowbytes(png_ptr, info_ptr);
|
|---|
| 1007 | rowbytes - number of bytes needed to hold a row
|
|---|
| 1008 |
|
|---|
| 1009 | signature = png_get_signature(png_ptr, info_ptr);
|
|---|
| 1010 | signature - holds the signature read from the
|
|---|
| 1011 | file (if any). The data is kept in
|
|---|
| 1012 | the same offset it would be if the
|
|---|
| 1013 | whole signature were read (i.e. if an
|
|---|
| 1014 | application had already read in 4
|
|---|
| 1015 | bytes of signature before starting
|
|---|
| 1016 | libpng, the remaining 4 bytes would
|
|---|
| 1017 | be in signature[4] through signature[7]
|
|---|
| 1018 | (see png_set_sig_bytes())).
|
|---|
| 1019 |
|
|---|
| 1020 | These are also important, but their validity depends on whether the chunk
|
|---|
| 1021 | has been read. The png_get_valid(png_ptr, info_ptr, PNG_INFO_<chunk>) and
|
|---|
| 1022 | png_get_<chunk>(png_ptr, info_ptr, ...) functions return non-zero if the
|
|---|
| 1023 | data has been read, or zero if it is missing. The parameters to the
|
|---|
| 1024 | png_get_<chunk> are set directly if they are simple data types, or a
|
|---|
| 1025 | pointer into the info_ptr is returned for any complex types.
|
|---|
| 1026 |
|
|---|
| 1027 | png_get_PLTE(png_ptr, info_ptr, &palette,
|
|---|
| 1028 | &num_palette);
|
|---|
| 1029 | palette - the palette for the file
|
|---|
| 1030 | (array of png_color)
|
|---|
| 1031 | num_palette - number of entries in the palette
|
|---|
| 1032 |
|
|---|
| 1033 | png_get_gAMA(png_ptr, info_ptr, &gamma);
|
|---|
| 1034 | gamma - the gamma the file is written
|
|---|
| 1035 | at (PNG_INFO_gAMA)
|
|---|
| 1036 |
|
|---|
| 1037 | png_get_sRGB(png_ptr, info_ptr, &srgb_intent);
|
|---|
| 1038 | srgb_intent - the rendering intent (PNG_INFO_sRGB)
|
|---|
| 1039 | The presence of the sRGB chunk
|
|---|
| 1040 | means that the pixel data is in the
|
|---|
| 1041 | sRGB color space. This chunk also
|
|---|
| 1042 | implies specific values of gAMA and
|
|---|
| 1043 | cHRM.
|
|---|
| 1044 |
|
|---|
| 1045 | png_get_iCCP(png_ptr, info_ptr, &name,
|
|---|
| 1046 | &compression_type, &profile, &proflen);
|
|---|
| 1047 | name - The profile name.
|
|---|
| 1048 | compression - The compression type; always
|
|---|
| 1049 | PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
|
|---|
| 1050 | You may give NULL to this argument to
|
|---|
| 1051 | ignore it.
|
|---|
| 1052 | profile - International Color Consortium color
|
|---|
| 1053 | profile data. May contain NULs.
|
|---|
| 1054 | proflen - length of profile data in bytes.
|
|---|
| 1055 |
|
|---|
| 1056 | png_get_sBIT(png_ptr, info_ptr, &sig_bit);
|
|---|
| 1057 | sig_bit - the number of significant bits for
|
|---|
| 1058 | (PNG_INFO_sBIT) each of the gray,
|
|---|
| 1059 | red, green, and blue channels,
|
|---|
| 1060 | whichever are appropriate for the
|
|---|
| 1061 | given color type (png_color_16)
|
|---|
| 1062 |
|
|---|
| 1063 | png_get_tRNS(png_ptr, info_ptr, &trans, &num_trans,
|
|---|
| 1064 | &trans_values);
|
|---|
| 1065 | trans - array of transparent
|
|---|
| 1066 | entries for palette (PNG_INFO_tRNS)
|
|---|
| 1067 | trans_values - graylevel or color sample values of
|
|---|
| 1068 | the single transparent color for
|
|---|
| 1069 | non-paletted images (PNG_INFO_tRNS)
|
|---|
| 1070 | num_trans - number of transparent entries
|
|---|
| 1071 | (PNG_INFO_tRNS)
|
|---|
| 1072 |
|
|---|
| 1073 | png_get_hIST(png_ptr, info_ptr, &hist);
|
|---|
| 1074 | (PNG_INFO_hIST)
|
|---|
| 1075 | hist - histogram of palette (array of
|
|---|
| 1076 | png_uint_16)
|
|---|
| 1077 |
|
|---|
| 1078 | png_get_tIME(png_ptr, info_ptr, &mod_time);
|
|---|
| 1079 | mod_time - time image was last modified
|
|---|
| 1080 | (PNG_VALID_tIME)
|
|---|
| 1081 |
|
|---|
| 1082 | png_get_bKGD(png_ptr, info_ptr, &background);
|
|---|
| 1083 | background - background color (PNG_VALID_bKGD)
|
|---|
| 1084 | valid 16-bit red, green and blue
|
|---|
| 1085 | values, regardless of color_type
|
|---|
| 1086 |
|
|---|
| 1087 | num_comments = png_get_text(png_ptr, info_ptr,
|
|---|
| 1088 | &text_ptr, &num_text);
|
|---|
| 1089 | num_comments - number of comments
|
|---|
| 1090 | text_ptr - array of png_text holding image
|
|---|
| 1091 | comments
|
|---|
| 1092 | text_ptr[i].compression - type of compression used
|
|---|
| 1093 | on "text" PNG_TEXT_COMPRESSION_NONE
|
|---|
| 1094 | PNG_TEXT_COMPRESSION_zTXt
|
|---|
| 1095 | PNG_ITXT_COMPRESSION_NONE
|
|---|
| 1096 | PNG_ITXT_COMPRESSION_zTXt
|
|---|
| 1097 | text_ptr[i].key - keyword for comment. Must contain
|
|---|
| 1098 | 1-79 characters.
|
|---|
| 1099 | text_ptr[i].text - text comments for current
|
|---|
| 1100 | keyword. Can be empty.
|
|---|
| 1101 | text_ptr[i].text_length - length of text string,
|
|---|
| 1102 | after decompression, 0 for iTXt
|
|---|
| 1103 | text_ptr[i].itxt_length - length of itxt string,
|
|---|
| 1104 | after decompression, 0 for tEXt/zTXt
|
|---|
| 1105 | text_ptr[i].lang - language of comment (empty
|
|---|
| 1106 | string for unknown).
|
|---|
| 1107 | text_ptr[i].lang_key - keyword in UTF-8
|
|---|
| 1108 | (empty string for unknown).
|
|---|
| 1109 | Note that the itxt_length, lang, and lang_key
|
|---|
| 1110 | members of the text_ptr structure only exist
|
|---|
| 1111 | when the library is built with iTXt chunk support.
|
|---|
| 1112 |
|
|---|
| 1113 | num_text - number of comments (same as
|
|---|
| 1114 | num_comments; you can put NULL here
|
|---|
| 1115 | to avoid the duplication)
|
|---|
| 1116 | Note while png_set_text() will accept text, language,
|
|---|
| 1117 | and translated keywords that can be NULL pointers, the
|
|---|
| 1118 | structure returned by png_get_text will always contain
|
|---|
| 1119 | regular zero-terminated C strings. They might be
|
|---|
| 1120 | empty strings but they will never be NULL pointers.
|
|---|
| 1121 |
|
|---|
| 1122 | num_spalettes = png_get_sPLT(png_ptr, info_ptr,
|
|---|
| 1123 | &palette_ptr);
|
|---|
| 1124 | palette_ptr - array of palette structures holding
|
|---|
| 1125 | contents of one or more sPLT chunks
|
|---|
| 1126 | read.
|
|---|
| 1127 | num_spalettes - number of sPLT chunks read.
|
|---|
| 1128 |
|
|---|
| 1129 | png_get_oFFs(png_ptr, info_ptr, &offset_x, &offset_y,
|
|---|
| 1130 | &unit_type);
|
|---|
| 1131 | offset_x - positive offset from the left edge
|
|---|
| 1132 | of the screen
|
|---|
| 1133 | offset_y - positive offset from the top edge
|
|---|
| 1134 | of the screen
|
|---|
| 1135 | unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
|
|---|
| 1136 |
|
|---|
| 1137 | png_get_pHYs(png_ptr, info_ptr, &res_x, &res_y,
|
|---|
| 1138 | &unit_type);
|
|---|
| 1139 | res_x - pixels/unit physical resolution in
|
|---|
| 1140 | x direction
|
|---|
| 1141 | res_y - pixels/unit physical resolution in
|
|---|
| 1142 | x direction
|
|---|
| 1143 | unit_type - PNG_RESOLUTION_UNKNOWN,
|
|---|
| 1144 | PNG_RESOLUTION_METER
|
|---|
| 1145 |
|
|---|
| 1146 | png_get_sCAL(png_ptr, info_ptr, &unit, &width,
|
|---|
| 1147 | &height)
|
|---|
| 1148 | unit - physical scale units (an integer)
|
|---|
| 1149 | width - width of a pixel in physical scale units
|
|---|
| 1150 | height - height of a pixel in physical scale units
|
|---|
| 1151 | (width and height are doubles)
|
|---|
| 1152 |
|
|---|
| 1153 | png_get_sCAL_s(png_ptr, info_ptr, &unit, &width,
|
|---|
| 1154 | &height)
|
|---|
| 1155 | unit - physical scale units (an integer)
|
|---|
| 1156 | width - width of a pixel in physical scale units
|
|---|
| 1157 | height - height of a pixel in physical scale units
|
|---|
| 1158 | (width and height are strings like "2.54")
|
|---|
| 1159 |
|
|---|
| 1160 | num_unknown_chunks = png_get_unknown_chunks(png_ptr,
|
|---|
| 1161 | info_ptr, &unknowns)
|
|---|
| 1162 | unknowns - array of png_unknown_chunk
|
|---|
| 1163 | structures holding unknown chunks
|
|---|
| 1164 | unknowns[i].name - name of unknown chunk
|
|---|
| 1165 | unknowns[i].data - data of unknown chunk
|
|---|
| 1166 | unknowns[i].size - size of unknown chunk's data
|
|---|
| 1167 | unknowns[i].location - position of chunk in file
|
|---|
| 1168 |
|
|---|
| 1169 | The value of "i" corresponds to the order in which the
|
|---|
| 1170 | chunks were read from the PNG file or inserted with the
|
|---|
| 1171 | png_set_unknown_chunks() function.
|
|---|
| 1172 |
|
|---|
| 1173 | The data from the pHYs chunk can be retrieved in several convenient
|
|---|
| 1174 | forms:
|
|---|
| 1175 |
|
|---|
| 1176 | res_x = png_get_x_pixels_per_meter(png_ptr,
|
|---|
| 1177 | info_ptr)
|
|---|
| 1178 | res_y = png_get_y_pixels_per_meter(png_ptr,
|
|---|
| 1179 | info_ptr)
|
|---|
| 1180 | res_x_and_y = png_get_pixels_per_meter(png_ptr,
|
|---|
| 1181 | info_ptr)
|
|---|
| 1182 | res_x = png_get_x_pixels_per_inch(png_ptr,
|
|---|
| 1183 | info_ptr)
|
|---|
| 1184 | res_y = png_get_y_pixels_per_inch(png_ptr,
|
|---|
| 1185 | info_ptr)
|
|---|
| 1186 | res_x_and_y = png_get_pixels_per_inch(png_ptr,
|
|---|
| 1187 | info_ptr)
|
|---|
| 1188 | aspect_ratio = png_get_pixel_aspect_ratio(png_ptr,
|
|---|
| 1189 | info_ptr)
|
|---|
| 1190 |
|
|---|
| 1191 | (Each of these returns 0 [signifying "unknown"] if
|
|---|
| 1192 | the data is not present or if res_x is 0;
|
|---|
| 1193 | res_x_and_y is 0 if res_x != res_y)
|
|---|
| 1194 |
|
|---|
| 1195 | The data from the oFFs chunk can be retrieved in several convenient
|
|---|
| 1196 | forms:
|
|---|
| 1197 |
|
|---|
| 1198 | x_offset = png_get_x_offset_microns(png_ptr, info_ptr);
|
|---|
| 1199 | y_offset = png_get_y_offset_microns(png_ptr, info_ptr);
|
|---|
| 1200 | x_offset = png_get_x_offset_inches(png_ptr, info_ptr);
|
|---|
| 1201 | y_offset = png_get_y_offset_inches(png_ptr, info_ptr);
|
|---|
| 1202 |
|
|---|
| 1203 | (Each of these returns 0 [signifying "unknown" if both
|
|---|
| 1204 | x and y are 0] if the data is not present or if the
|
|---|
| 1205 | chunk is present but the unit is the pixel)
|
|---|
| 1206 |
|
|---|
| 1207 | For more information, see the png_info definition in png.h and the
|
|---|
| 1208 | PNG specification for chunk contents. Be careful with trusting
|
|---|
| 1209 | rowbytes, as some of the transformations could increase the space
|
|---|
| 1210 | needed to hold a row (expand, filler, gray_to_rgb, etc.).
|
|---|
| 1211 | See png_read_update_info(), below.
|
|---|
| 1212 |
|
|---|
| 1213 | A quick word about text_ptr and num_text. PNG stores comments in
|
|---|
| 1214 | keyword/text pairs, one pair per chunk, with no limit on the number
|
|---|
| 1215 | of text chunks, and a 2^31 byte limit on their size. While there are
|
|---|
| 1216 | suggested keywords, there is no requirement to restrict the use to these
|
|---|
| 1217 | strings. It is strongly suggested that keywords and text be sensible
|
|---|
| 1218 | to humans (that's the point), so don't use abbreviations. Non-printing
|
|---|
| 1219 | symbols are not allowed. See the PNG specification for more details.
|
|---|
| 1220 | There is also no requirement to have text after the keyword.
|
|---|
| 1221 |
|
|---|
| 1222 | Keywords should be limited to 79 Latin-1 characters without leading or
|
|---|
| 1223 | trailing spaces, but non-consecutive spaces are allowed within the
|
|---|
| 1224 | keyword. It is possible to have the same keyword any number of times.
|
|---|
| 1225 | The text_ptr is an array of png_text structures, each holding a
|
|---|
| 1226 | pointer to a language string, a pointer to a keyword and a pointer to
|
|---|
| 1227 | a text string. The text string, language code, and translated
|
|---|
| 1228 | keyword may be empty or NULL pointers. The keyword/text
|
|---|
| 1229 | pairs are put into the array in the order that they are received.
|
|---|
| 1230 | However, some or all of the text chunks may be after the image, so, to
|
|---|
| 1231 | make sure you have read all the text chunks, don't mess with these
|
|---|
| 1232 | until after you read the stuff after the image. This will be
|
|---|
| 1233 | mentioned again below in the discussion that goes with png_read_end().
|
|---|
| 1234 |
|
|---|
| 1235 | .SS Input transformations
|
|---|
| 1236 |
|
|---|
| 1237 | After you've read the header information, you can set up the library
|
|---|
| 1238 | to handle any special transformations of the image data. The various
|
|---|
| 1239 | ways to transform the data will be described in the order that they
|
|---|
| 1240 | should occur. This is important, as some of these change the color
|
|---|
| 1241 | type and/or bit depth of the data, and some others only work on
|
|---|
| 1242 | certain color types and bit depths. Even though each transformation
|
|---|
| 1243 | checks to see if it has data that it can do something with, you should
|
|---|
| 1244 | make sure to only enable a transformation if it will be valid for the
|
|---|
| 1245 | data. For example, don't swap red and blue on grayscale data.
|
|---|
| 1246 |
|
|---|
| 1247 | The colors used for the background and transparency values should be
|
|---|
| 1248 | supplied in the same format/depth as the current image data. They
|
|---|
| 1249 | are stored in the same format/depth as the image data in a bKGD or tRNS
|
|---|
| 1250 | chunk, so this is what libpng expects for this data. The colors are
|
|---|
| 1251 | transformed to keep in sync with the image data when an application
|
|---|
| 1252 | calls the png_read_update_info() routine (see below).
|
|---|
| 1253 |
|
|---|
| 1254 | Data will be decoded into the supplied row buffers packed into bytes
|
|---|
| 1255 | unless the library has been told to transform it into another format.
|
|---|
| 1256 | For example, 4 bit/pixel paletted or grayscale data will be returned
|
|---|
| 1257 | 2 pixels/byte with the leftmost pixel in the high-order bits of the
|
|---|
| 1258 | byte, unless png_set_packing() is called. 8-bit RGB data will be stored
|
|---|
| 1259 | in RGB RGB RGB format unless png_set_filler() or png_set_add_alpha()
|
|---|
| 1260 | is called to insert filler bytes, either before or after each RGB triplet.
|
|---|
| 1261 | 16-bit RGB data will be returned RRGGBB RRGGBB, with the most significant
|
|---|
| 1262 | byte of the color value first, unless png_set_strip_16() is called to
|
|---|
| 1263 | transform it to regular RGB RGB triplets, or png_set_filler() or
|
|---|
| 1264 | png_set_add alpha() is called to insert filler bytes, either before or
|
|---|
| 1265 | after each RRGGBB triplet. Similarly, 8-bit or 16-bit grayscale data can
|
|---|
| 1266 | be modified with
|
|---|
| 1267 | png_set_filler(), png_set_add_alpha(), or png_set_strip_16().
|
|---|
| 1268 |
|
|---|
| 1269 | The following code transforms grayscale images of less than 8 to 8 bits,
|
|---|
| 1270 | changes paletted images to RGB, and adds a full alpha channel if there is
|
|---|
| 1271 | transparency information in a tRNS chunk. This is most useful on
|
|---|
| 1272 | grayscale images with bit depths of 2 or 4 or if there is a multiple-image
|
|---|
| 1273 | viewing application that wishes to treat all images in the same way.
|
|---|
| 1274 |
|
|---|
| 1275 | if (color_type == PNG_COLOR_TYPE_PALETTE)
|
|---|
| 1276 | png_set_palette_to_rgb(png_ptr);
|
|---|
| 1277 |
|
|---|
| 1278 | if (color_type == PNG_COLOR_TYPE_GRAY &&
|
|---|
| 1279 | bit_depth < 8) png_set_expand_gray_1_2_4_to_8(png_ptr);
|
|---|
| 1280 |
|
|---|
| 1281 | if (png_get_valid(png_ptr, info_ptr,
|
|---|
| 1282 | PNG_INFO_tRNS)) png_set_tRNS_to_alpha(png_ptr);
|
|---|
| 1283 |
|
|---|
| 1284 | These three functions are actually aliases for png_set_expand(), added
|
|---|
| 1285 | in libpng version 1.0.4, with the function names expanded to improve code
|
|---|
| 1286 | readability. In some future version they may actually do different
|
|---|
| 1287 | things.
|
|---|
| 1288 |
|
|---|
| 1289 | As of libpng version 1.2.9, png_set_expand_gray_1_2_4_to_8() was
|
|---|
| 1290 | added. It expands the sample depth without changing tRNS to alpha.
|
|---|
| 1291 |
|
|---|
| 1292 | As of libpng version 1.2.54, not all possible expansions are supported.
|
|---|
| 1293 |
|
|---|
| 1294 | In the following table, the 01 means grayscale with depth<8, 31 means
|
|---|
| 1295 | indexed with depth<8, other numerals represent the color type, "T" means
|
|---|
| 1296 | the tRNS chunk is present, A means an alpha channel is present, and O
|
|---|
| 1297 | means tRNS or alpha is present but all pixels in the image are opaque.
|
|---|
| 1298 |
|
|---|
| 1299 | FROM 01 31 0 0T 0O 2 2T 2O 3 3T 3O 4A 4O 6A 6O
|
|---|
| 1300 | TO
|
|---|
| 1301 | 01 -
|
|---|
| 1302 | 31 -
|
|---|
| 1303 | 0 1 -
|
|---|
| 1304 | 0T -
|
|---|
| 1305 | 0O -
|
|---|
| 1306 | 2 GX -
|
|---|
| 1307 | 2T -
|
|---|
| 1308 | 2O -
|
|---|
| 1309 | 3 1 -
|
|---|
| 1310 | 3T -
|
|---|
| 1311 | 3O -
|
|---|
| 1312 | 4A T -
|
|---|
| 1313 | 4O -
|
|---|
| 1314 | 6A GX TX TX -
|
|---|
| 1315 | 6O GX TX -
|
|---|
| 1316 |
|
|---|
| 1317 | Within the matrix,
|
|---|
| 1318 | "-" means the transformation is not supported.
|
|---|
| 1319 | "X" means the transformation is obtained by png_set_expand().
|
|---|
| 1320 | "1" means the transformation is obtained by
|
|---|
| 1321 | png_set_expand_gray_1_2_4_to_8
|
|---|
| 1322 | "G" means the transformation is obtained by
|
|---|
| 1323 | png_set_gray_to_rgb().
|
|---|
| 1324 | "P" means the transformation is obtained by
|
|---|
| 1325 | png_set_expand_palette_to_rgb().
|
|---|
| 1326 | "T" means the transformation is obtained by
|
|---|
| 1327 | png_set_tRNS_to_alpha().
|
|---|
| 1328 |
|
|---|
| 1329 | PNG can have files with 16 bits per channel. If you only can handle
|
|---|
| 1330 | 8 bits per channel, this will strip the pixels down to 8 bit.
|
|---|
| 1331 |
|
|---|
| 1332 | if (bit_depth == 16)
|
|---|
| 1333 | png_set_strip_16(png_ptr);
|
|---|
| 1334 |
|
|---|
| 1335 | If, for some reason, you don't need the alpha channel on an image,
|
|---|
| 1336 | and you want to remove it rather than combining it with the background
|
|---|
| 1337 | (but the image author certainly had in mind that you *would* combine
|
|---|
| 1338 | it with the background, so that's what you should probably do):
|
|---|
| 1339 |
|
|---|
| 1340 | if (color_type & PNG_COLOR_MASK_ALPHA)
|
|---|
| 1341 | png_set_strip_alpha(png_ptr);
|
|---|
| 1342 |
|
|---|
| 1343 | In PNG files, the alpha channel in an image
|
|---|
| 1344 | is the level of opacity. If you need the alpha channel in an image to
|
|---|
| 1345 | be the level of transparency instead of opacity, you can invert the
|
|---|
| 1346 | alpha channel (or the tRNS chunk data) after it's read, so that 0 is
|
|---|
| 1347 | fully opaque and 255 (in 8-bit or paletted images) or 65535 (in 16-bit
|
|---|
| 1348 | images) is fully transparent, with
|
|---|
| 1349 |
|
|---|
| 1350 | png_set_invert_alpha(png_ptr);
|
|---|
| 1351 |
|
|---|
| 1352 | The PNG format only supports pixels with postmultiplied alpha.
|
|---|
| 1353 | If you want to replace the pixels, after reading them, with pixels
|
|---|
| 1354 | that have premultiplied color samples, you can do this with
|
|---|
| 1355 |
|
|---|
| 1356 | png_set_premultiply_alpha(png_ptr);
|
|---|
| 1357 |
|
|---|
| 1358 | If you do this, any input with a tRNS chunk will be expanded to
|
|---|
| 1359 | have an alpha channel.
|
|---|
| 1360 |
|
|---|
| 1361 | PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
|
|---|
| 1362 | they can, resulting in, for example, 8 pixels per byte for 1 bit
|
|---|
| 1363 | files. This code expands to 1 pixel per byte without changing the
|
|---|
| 1364 | values of the pixels:
|
|---|
| 1365 |
|
|---|
| 1366 | if (bit_depth < 8)
|
|---|
| 1367 | png_set_packing(png_ptr);
|
|---|
| 1368 |
|
|---|
| 1369 | PNG files have possible bit depths of 1, 2, 4, 8, and 16. All pixels
|
|---|
| 1370 | stored in a PNG image have been "scaled" or "shifted" up to the next
|
|---|
| 1371 | higher possible bit depth (e.g. from 5 bits/sample in the range [0,31]
|
|---|
| 1372 | to 8 bits/sample in the range [0, 255]). However, it is also possible
|
|---|
| 1373 | to convert the PNG pixel data back to the original bit depth of the
|
|---|
| 1374 | image. This call reduces the pixels back down to the original bit depth:
|
|---|
| 1375 |
|
|---|
| 1376 | png_color_8p sig_bit;
|
|---|
| 1377 |
|
|---|
| 1378 | if (png_get_sBIT(png_ptr, info_ptr, &sig_bit))
|
|---|
| 1379 | png_set_shift(png_ptr, sig_bit);
|
|---|
| 1380 |
|
|---|
| 1381 | PNG files store 3-color pixels in red, green, blue order. This code
|
|---|
| 1382 | changes the storage of the pixels to blue, green, red:
|
|---|
| 1383 |
|
|---|
| 1384 | if (color_type == PNG_COLOR_TYPE_RGB ||
|
|---|
| 1385 | color_type == PNG_COLOR_TYPE_RGB_ALPHA)
|
|---|
| 1386 | png_set_bgr(png_ptr);
|
|---|
| 1387 |
|
|---|
| 1388 | PNG files store RGB pixels packed into 3 or 6 bytes. This code expands them
|
|---|
| 1389 | into 4 or 8 bytes for windowing systems that need them in this format:
|
|---|
| 1390 |
|
|---|
| 1391 | if (color_type == PNG_COLOR_TYPE_RGB)
|
|---|
| 1392 | png_set_filler(png_ptr, filler, PNG_FILLER_BEFORE);
|
|---|
| 1393 |
|
|---|
| 1394 | where "filler" is the 8 or 16-bit number to fill with, and the location is
|
|---|
| 1395 | either PNG_FILLER_BEFORE or PNG_FILLER_AFTER, depending upon whether
|
|---|
| 1396 | you want the filler before the RGB or after. This transformation
|
|---|
| 1397 | does not affect images that already have full alpha channels. To add an
|
|---|
| 1398 | opaque alpha channel, use filler=0xff or 0xffff and PNG_FILLER_AFTER which
|
|---|
| 1399 | will generate RGBA pixels.
|
|---|
| 1400 |
|
|---|
| 1401 | Note that png_set_filler() does not change the color type. If you want
|
|---|
| 1402 | to do that, you can add a true alpha channel with
|
|---|
| 1403 |
|
|---|
| 1404 | if (color_type == PNG_COLOR_TYPE_RGB ||
|
|---|
| 1405 | color_type == PNG_COLOR_TYPE_GRAY)
|
|---|
| 1406 | png_set_add_alpha(png_ptr, filler, PNG_FILLER_AFTER);
|
|---|
| 1407 |
|
|---|
| 1408 | where "filler" contains the alpha value to assign to each pixel.
|
|---|
| 1409 | This function was added in libpng-1.2.7.
|
|---|
| 1410 |
|
|---|
| 1411 | If you are reading an image with an alpha channel, and you need the
|
|---|
| 1412 | data as ARGB instead of the normal PNG format RGBA:
|
|---|
| 1413 |
|
|---|
| 1414 | if (color_type == PNG_COLOR_TYPE_RGB_ALPHA)
|
|---|
| 1415 | png_set_swap_alpha(png_ptr);
|
|---|
| 1416 |
|
|---|
| 1417 | For some uses, you may want a grayscale image to be represented as
|
|---|
| 1418 | RGB. This code will do that conversion:
|
|---|
| 1419 |
|
|---|
| 1420 | if (color_type == PNG_COLOR_TYPE_GRAY ||
|
|---|
| 1421 | color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
|
|---|
| 1422 | png_set_gray_to_rgb(png_ptr);
|
|---|
| 1423 |
|
|---|
| 1424 | Conversely, you can convert an RGB or RGBA image to grayscale or grayscale
|
|---|
| 1425 | with alpha.
|
|---|
| 1426 |
|
|---|
| 1427 | if (color_type == PNG_COLOR_TYPE_RGB ||
|
|---|
| 1428 | color_type == PNG_COLOR_TYPE_RGB_ALPHA)
|
|---|
| 1429 | png_set_rgb_to_gray_fixed(png_ptr, error_action,
|
|---|
| 1430 | int red_weight, int green_weight);
|
|---|
| 1431 |
|
|---|
| 1432 | error_action = 1: silently do the conversion
|
|---|
| 1433 | error_action = 2: issue a warning if the original
|
|---|
| 1434 | image has any pixel where
|
|---|
| 1435 | red != green or red != blue
|
|---|
| 1436 | error_action = 3: issue an error and abort the
|
|---|
| 1437 | conversion if the original
|
|---|
| 1438 | image has any pixel where
|
|---|
| 1439 | red != green or red != blue
|
|---|
| 1440 |
|
|---|
| 1441 | red_weight: weight of red component times 100000
|
|---|
| 1442 | green_weight: weight of green component times 100000
|
|---|
| 1443 | If either weight is negative, default
|
|---|
| 1444 | weights (21268, 71514) are used.
|
|---|
| 1445 |
|
|---|
| 1446 | If you have set error_action = 1 or 2, you can
|
|---|
| 1447 | later check whether the image really was gray, after processing
|
|---|
| 1448 | the image rows, with the png_get_rgb_to_gray_status(png_ptr) function.
|
|---|
| 1449 | It will return a png_byte that is zero if the image was gray or
|
|---|
| 1450 | 1 if there were any non-gray pixels. bKGD and sBIT data
|
|---|
| 1451 | will be silently converted to grayscale, using the green channel
|
|---|
| 1452 | data, regardless of the error_action setting.
|
|---|
| 1453 |
|
|---|
| 1454 | With red_weight+green_weight<=100000,
|
|---|
| 1455 | the normalized graylevel is computed:
|
|---|
| 1456 |
|
|---|
| 1457 | int rw = red_weight * 65536;
|
|---|
| 1458 | int gw = green_weight * 65536;
|
|---|
| 1459 | int bw = 65536 - (rw + gw);
|
|---|
| 1460 | gray = (rw*red + gw*green + bw*blue)/65536;
|
|---|
| 1461 |
|
|---|
| 1462 | The default values come from the PNG file cHRM chunk if present; otherwise, the
|
|---|
| 1463 | defaults correspond to the ITU-R recommendation 709, and also the sRGB color
|
|---|
| 1464 | space, as recommended in the Charles Poynton's Colour FAQ,
|
|---|
| 1465 | Copyright (c) 2006-11-28 Charles Poynton, in section 9:
|
|---|
| 1466 |
|
|---|
| 1467 | <http://www.poynton.com/notes/colour_and_gamma/ColorFAQ.html#RTFToC9>
|
|---|
| 1468 |
|
|---|
| 1469 | Y = 0.212671 * R + 0.715160 * G + 0.072169 * B
|
|---|
| 1470 |
|
|---|
| 1471 | Libpng approximates this with
|
|---|
| 1472 |
|
|---|
| 1473 | Y = 0.21268 * R + 0.7151 * G + 0.07217 * B
|
|---|
| 1474 |
|
|---|
| 1475 | which can be expressed with integers as
|
|---|
| 1476 |
|
|---|
| 1477 | Y = (6969 * R + 23434 * G + 2365 * B)/32768
|
|---|
| 1478 |
|
|---|
| 1479 | The calculation is done in a linear colorspace, if the image gamma
|
|---|
| 1480 | is known.
|
|---|
| 1481 |
|
|---|
| 1482 | If you have a grayscale and you are using png_set_expand_depth(),
|
|---|
| 1483 | png_set_expand(), or png_set_gray_to_rgb to change to truecolor or to
|
|---|
| 1484 | a higher bit-depth, you must either supply the background color as a gray
|
|---|
| 1485 | value at the original file bit-depth (need_expand = 1) or else supply the
|
|---|
| 1486 | background color as an RGB triplet at the final, expanded bit depth
|
|---|
| 1487 | (need_expand = 0). Similarly, if you are reading a paletted image, you
|
|---|
| 1488 | must either supply the background color as a palette index (need_expand = 1)
|
|---|
| 1489 | or as an RGB triplet that may or may not be in the palette (need_expand = 0).
|
|---|
| 1490 |
|
|---|
| 1491 | png_color_16 my_background;
|
|---|
| 1492 | png_color_16p image_background;
|
|---|
| 1493 |
|
|---|
| 1494 | if (png_get_bKGD(png_ptr, info_ptr, &image_background))
|
|---|
| 1495 | png_set_background(png_ptr, image_background,
|
|---|
| 1496 | PNG_BACKGROUND_GAMMA_FILE, 1, 1.0);
|
|---|
| 1497 | else
|
|---|
| 1498 | png_set_background(png_ptr, &my_background,
|
|---|
| 1499 | PNG_BACKGROUND_GAMMA_SCREEN, 0, 1.0);
|
|---|
| 1500 |
|
|---|
| 1501 | The png_set_background() function tells libpng to composite images
|
|---|
| 1502 | with alpha or simple transparency against the supplied background
|
|---|
| 1503 | color. If the PNG file contains a bKGD chunk (PNG_INFO_bKGD valid),
|
|---|
| 1504 | you may use this color, or supply another color more suitable for
|
|---|
| 1505 | the current display (e.g., the background color from a web page). You
|
|---|
| 1506 | need to tell libpng whether the color is in the gamma space of the
|
|---|
| 1507 | display (PNG_BACKGROUND_GAMMA_SCREEN for colors you supply), the file
|
|---|
| 1508 | (PNG_BACKGROUND_GAMMA_FILE for colors from the bKGD chunk), or one
|
|---|
| 1509 | that is neither of these gammas (PNG_BACKGROUND_GAMMA_UNIQUE - I don't
|
|---|
| 1510 | know why anyone would use this, but it's here).
|
|---|
| 1511 |
|
|---|
| 1512 | To properly display PNG images on any kind of system, the application needs
|
|---|
| 1513 | to know what the display gamma is. Ideally, the user will know this, and
|
|---|
| 1514 | the application will allow them to set it. One method of allowing the user
|
|---|
| 1515 | to set the display gamma separately for each system is to check for a
|
|---|
| 1516 | SCREEN_GAMMA or DISPLAY_GAMMA environment variable, which will hopefully be
|
|---|
| 1517 | correctly set.
|
|---|
| 1518 |
|
|---|
| 1519 | Note that display_gamma is the overall gamma correction required to produce
|
|---|
| 1520 | pleasing results, which depends on the lighting conditions in the surrounding
|
|---|
| 1521 | environment. In a dim or brightly lit room, no compensation other than
|
|---|
| 1522 | the physical gamma exponent of the monitor is needed, while in a dark room
|
|---|
| 1523 | a slightly smaller exponent is better.
|
|---|
| 1524 |
|
|---|
| 1525 | double gamma, screen_gamma;
|
|---|
| 1526 |
|
|---|
| 1527 | if (/* We have a user-defined screen
|
|---|
| 1528 | gamma value */)
|
|---|
| 1529 | {
|
|---|
| 1530 | screen_gamma = user_defined_screen_gamma;
|
|---|
| 1531 | }
|
|---|
| 1532 | /* One way that applications can share the same
|
|---|
| 1533 | screen gamma value */
|
|---|
| 1534 | else if ((gamma_str = getenv("SCREEN_GAMMA"))
|
|---|
| 1535 | != NULL)
|
|---|
| 1536 | {
|
|---|
| 1537 | screen_gamma = (double)atof(gamma_str);
|
|---|
| 1538 | }
|
|---|
| 1539 | /* If we don't have another value */
|
|---|
| 1540 | else
|
|---|
| 1541 | {
|
|---|
| 1542 | screen_gamma = 2.2; /* A good guess for a
|
|---|
| 1543 | PC monitor in a bright office or a dim room */
|
|---|
| 1544 | screen_gamma = 2.0; /* A good guess for a
|
|---|
| 1545 | PC monitor in a dark room */
|
|---|
| 1546 | screen_gamma = 1.7 or 1.0; /* A good
|
|---|
| 1547 | guess for Mac systems */
|
|---|
| 1548 | }
|
|---|
| 1549 |
|
|---|
| 1550 | The png_set_gamma() function handles gamma transformations of the data.
|
|---|
| 1551 | Pass both the file gamma and the current screen_gamma. If the file does
|
|---|
| 1552 | not have a gamma value, you can pass one anyway if you have an idea what
|
|---|
| 1553 | it is (usually 0.45455 is a good guess for GIF images on PCs). Note
|
|---|
| 1554 | that file gammas are inverted from screen gammas. See the discussions
|
|---|
| 1555 | on gamma in the PNG specification for an excellent description of what
|
|---|
| 1556 | gamma is, and why all applications should support it. It is strongly
|
|---|
| 1557 | recommended that PNG viewers support gamma correction.
|
|---|
| 1558 |
|
|---|
| 1559 | if (png_get_gAMA(png_ptr, info_ptr, &gamma))
|
|---|
| 1560 | png_set_gamma(png_ptr, screen_gamma, gamma);
|
|---|
| 1561 | else
|
|---|
| 1562 | png_set_gamma(png_ptr, screen_gamma, 0.45455);
|
|---|
| 1563 |
|
|---|
| 1564 | If you need to reduce an RGB file to a paletted file, or if a paletted
|
|---|
| 1565 | file has more entries then will fit on your screen, png_set_dither()
|
|---|
| 1566 | will do that. Note that this is a simple match dither that merely
|
|---|
| 1567 | finds the closest color available. This should work fairly well with
|
|---|
| 1568 | optimized palettes, and fairly badly with linear color cubes. If you
|
|---|
| 1569 | pass a palette that is larger then maximum_colors, the file will
|
|---|
| 1570 | reduce the number of colors in the palette so it will fit into
|
|---|
| 1571 | maximum_colors. If there is a histogram, it will use it to make
|
|---|
| 1572 | more intelligent choices when reducing the palette. If there is no
|
|---|
| 1573 | histogram, it may not do as good a job.
|
|---|
| 1574 |
|
|---|
| 1575 | if (color_type & PNG_COLOR_MASK_COLOR)
|
|---|
| 1576 | {
|
|---|
| 1577 | if (png_get_valid(png_ptr, info_ptr,
|
|---|
| 1578 | PNG_INFO_PLTE))
|
|---|
| 1579 | {
|
|---|
| 1580 | png_uint_16p histogram = NULL;
|
|---|
| 1581 |
|
|---|
| 1582 | png_get_hIST(png_ptr, info_ptr,
|
|---|
| 1583 | &histogram);
|
|---|
| 1584 | png_set_dither(png_ptr, palette, num_palette,
|
|---|
| 1585 | max_screen_colors, histogram, 1);
|
|---|
| 1586 | }
|
|---|
| 1587 | else
|
|---|
| 1588 | {
|
|---|
| 1589 | png_color std_color_cube[MAX_SCREEN_COLORS] =
|
|---|
| 1590 | { ... colors ... };
|
|---|
| 1591 |
|
|---|
| 1592 | png_set_dither(png_ptr, std_color_cube,
|
|---|
| 1593 | MAX_SCREEN_COLORS, MAX_SCREEN_COLORS,
|
|---|
| 1594 | NULL,0);
|
|---|
| 1595 | }
|
|---|
| 1596 | }
|
|---|
| 1597 |
|
|---|
| 1598 | PNG files describe monochrome as black being zero and white being one.
|
|---|
| 1599 | The following code will reverse this (make black be one and white be
|
|---|
| 1600 | zero):
|
|---|
| 1601 |
|
|---|
| 1602 | if (bit_depth == 1 && color_type == PNG_COLOR_TYPE_GRAY)
|
|---|
| 1603 | png_set_invert_mono(png_ptr);
|
|---|
| 1604 |
|
|---|
| 1605 | This function can also be used to invert grayscale and gray-alpha images:
|
|---|
| 1606 |
|
|---|
| 1607 | if (color_type == PNG_COLOR_TYPE_GRAY ||
|
|---|
| 1608 | color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
|
|---|
| 1609 | png_set_invert_mono(png_ptr);
|
|---|
| 1610 |
|
|---|
| 1611 | PNG files store 16 bit pixels in network byte order (big-endian,
|
|---|
| 1612 | ie. most significant bits first). This code changes the storage to the
|
|---|
| 1613 | other way (little-endian, i.e. least significant bits first, the
|
|---|
| 1614 | way PCs store them):
|
|---|
| 1615 |
|
|---|
| 1616 | if (bit_depth == 16)
|
|---|
| 1617 | png_set_swap(png_ptr);
|
|---|
| 1618 |
|
|---|
| 1619 | If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
|
|---|
| 1620 | need to change the order the pixels are packed into bytes, you can use:
|
|---|
| 1621 |
|
|---|
| 1622 | if (bit_depth < 8)
|
|---|
| 1623 | png_set_packswap(png_ptr);
|
|---|
| 1624 |
|
|---|
| 1625 | Finally, you can write your own transformation function if none of
|
|---|
| 1626 | the existing ones meets your needs. This is done by setting a callback
|
|---|
| 1627 | with
|
|---|
| 1628 |
|
|---|
| 1629 | png_set_read_user_transform_fn(png_ptr,
|
|---|
| 1630 | read_transform_fn);
|
|---|
| 1631 |
|
|---|
| 1632 | You must supply the function
|
|---|
| 1633 |
|
|---|
| 1634 | void read_transform_fn(png_ptr ptr, row_info_ptr
|
|---|
| 1635 | row_info, png_bytep data)
|
|---|
| 1636 |
|
|---|
| 1637 | See pngtest.c for a working example. Your function will be called
|
|---|
| 1638 | after all of the other transformations have been processed.
|
|---|
| 1639 |
|
|---|
| 1640 | You can also set up a pointer to a user structure for use by your
|
|---|
| 1641 | callback function, and you can inform libpng that your transform
|
|---|
| 1642 | function will change the number of channels or bit depth with the
|
|---|
| 1643 | function
|
|---|
| 1644 |
|
|---|
| 1645 | png_set_user_transform_info(png_ptr, user_ptr,
|
|---|
| 1646 | user_depth, user_channels);
|
|---|
| 1647 |
|
|---|
| 1648 | The user's application, not libpng, is responsible for allocating and
|
|---|
| 1649 | freeing any memory required for the user structure.
|
|---|
| 1650 |
|
|---|
| 1651 | You can retrieve the pointer via the function
|
|---|
| 1652 | png_get_user_transform_ptr(). For example:
|
|---|
| 1653 |
|
|---|
| 1654 | voidp read_user_transform_ptr =
|
|---|
| 1655 | png_get_user_transform_ptr(png_ptr);
|
|---|
| 1656 |
|
|---|
| 1657 | The last thing to handle is interlacing; this is covered in detail below,
|
|---|
| 1658 | but you must call the function here if you want libpng to handle expansion
|
|---|
| 1659 | of the interlaced image.
|
|---|
| 1660 |
|
|---|
| 1661 | number_of_passes = png_set_interlace_handling(png_ptr);
|
|---|
| 1662 |
|
|---|
| 1663 | After setting the transformations, libpng can update your png_info
|
|---|
| 1664 | structure to reflect any transformations you've requested with this
|
|---|
| 1665 | call. This is most useful to update the info structure's rowbytes
|
|---|
| 1666 | field so you can use it to allocate your image memory. This function
|
|---|
| 1667 | will also update your palette with the correct screen_gamma and
|
|---|
| 1668 | background if these have been given with the calls above.
|
|---|
| 1669 |
|
|---|
| 1670 | png_read_update_info(png_ptr, info_ptr);
|
|---|
| 1671 |
|
|---|
| 1672 | After you call png_read_update_info(), you can allocate any
|
|---|
| 1673 | memory you need to hold the image. The row data is simply
|
|---|
| 1674 | raw byte data for all forms of images. As the actual allocation
|
|---|
| 1675 | varies among applications, no example will be given. If you
|
|---|
| 1676 | are allocating one large chunk, you will need to build an
|
|---|
| 1677 | array of pointers to each row, as it will be needed for some
|
|---|
| 1678 | of the functions below.
|
|---|
| 1679 |
|
|---|
| 1680 | .SS Reading image data
|
|---|
| 1681 |
|
|---|
| 1682 | After you've allocated memory, you can read the image data.
|
|---|
| 1683 | The simplest way to do this is in one function call. If you are
|
|---|
| 1684 | allocating enough memory to hold the whole image, you can just
|
|---|
| 1685 | call png_read_image() and libpng will read in all the image data
|
|---|
| 1686 | and put it in the memory area supplied. You will need to pass in
|
|---|
| 1687 | an array of pointers to each row.
|
|---|
| 1688 |
|
|---|
| 1689 | This function automatically handles interlacing, so you don't need
|
|---|
| 1690 | to call png_set_interlace_handling() or call this function multiple
|
|---|
| 1691 | times, or any of that other stuff necessary with png_read_rows().
|
|---|
| 1692 |
|
|---|
| 1693 | png_read_image(png_ptr, row_pointers);
|
|---|
| 1694 |
|
|---|
| 1695 | where row_pointers is:
|
|---|
| 1696 |
|
|---|
| 1697 | png_bytep row_pointers[height];
|
|---|
| 1698 |
|
|---|
| 1699 | You can point to void or char or whatever you use for pixels.
|
|---|
| 1700 |
|
|---|
| 1701 | If you don't want to read in the whole image at once, you can
|
|---|
| 1702 | use png_read_rows() instead. If there is no interlacing (check
|
|---|
| 1703 | interlace_type == PNG_INTERLACE_NONE), this is simple:
|
|---|
| 1704 |
|
|---|
| 1705 | png_read_rows(png_ptr, row_pointers, NULL,
|
|---|
| 1706 | number_of_rows);
|
|---|
| 1707 |
|
|---|
| 1708 | where row_pointers is the same as in the png_read_image() call.
|
|---|
| 1709 |
|
|---|
| 1710 | If you are doing this just one row at a time, you can do this with
|
|---|
| 1711 | a single row_pointer instead of an array of row_pointers:
|
|---|
| 1712 |
|
|---|
| 1713 | png_bytep row_pointer = row;
|
|---|
| 1714 | png_read_row(png_ptr, row_pointer, NULL);
|
|---|
| 1715 |
|
|---|
| 1716 | If the file is interlaced (interlace_type != 0 in the IHDR chunk), things
|
|---|
| 1717 | get somewhat harder. The only current (PNG Specification version 1.2)
|
|---|
| 1718 | interlacing type for PNG is (interlace_type == PNG_INTERLACE_ADAM7)
|
|---|
| 1719 | is a somewhat complicated 2D interlace scheme, known as Adam7, that
|
|---|
| 1720 | breaks down an image into seven smaller images of varying size, based
|
|---|
| 1721 | on an 8x8 grid.
|
|---|
| 1722 |
|
|---|
| 1723 | libpng can fill out those images or it can give them to you "as is".
|
|---|
| 1724 | If you want them filled out, there are two ways to do that. The one
|
|---|
| 1725 | mentioned in the PNG specification is to expand each pixel to cover
|
|---|
| 1726 | those pixels that have not been read yet (the "rectangle" method).
|
|---|
| 1727 | This results in a blocky image for the first pass, which gradually
|
|---|
| 1728 | smooths out as more pixels are read. The other method is the "sparkle"
|
|---|
| 1729 | method, where pixels are drawn only in their final locations, with the
|
|---|
| 1730 | rest of the image remaining whatever colors they were initialized to
|
|---|
| 1731 | before the start of the read. The first method usually looks better,
|
|---|
| 1732 | but tends to be slower, as there are more pixels to put in the rows.
|
|---|
| 1733 |
|
|---|
| 1734 | If you don't want libpng to handle the interlacing details, just call
|
|---|
| 1735 | png_read_rows() seven times to read in all seven images. Each of the
|
|---|
| 1736 | images is a valid image by itself, or they can all be combined on an
|
|---|
| 1737 | 8x8 grid to form a single image (although if you intend to combine them
|
|---|
| 1738 | you would be far better off using the libpng interlace handling).
|
|---|
| 1739 |
|
|---|
| 1740 | The first pass will return an image 1/8 as wide as the entire image
|
|---|
| 1741 | (every 8th column starting in column 0) and 1/8 as high as the original
|
|---|
| 1742 | (every 8th row starting in row 0), the second will be 1/8 as wide
|
|---|
| 1743 | (starting in column 4) and 1/8 as high (also starting in row 0). The
|
|---|
| 1744 | third pass will be 1/4 as wide (every 4th pixel starting in column 0) and
|
|---|
| 1745 | 1/8 as high (every 8th row starting in row 4), and the fourth pass will
|
|---|
| 1746 | be 1/4 as wide and 1/4 as high (every 4th column starting in column 2,
|
|---|
| 1747 | and every 4th row starting in row 0). The fifth pass will return an
|
|---|
| 1748 | image 1/2 as wide, and 1/4 as high (starting at column 0 and row 2),
|
|---|
| 1749 | while the sixth pass will be 1/2 as wide and 1/2 as high as the original
|
|---|
| 1750 | (starting in column 1 and row 0). The seventh and final pass will be as
|
|---|
| 1751 | wide as the original, and 1/2 as high, containing all of the odd
|
|---|
| 1752 | numbered scanlines. Phew!
|
|---|
| 1753 |
|
|---|
| 1754 | If you want libpng to expand the images, call this before calling
|
|---|
| 1755 | png_start_read_image() or png_read_update_info():
|
|---|
| 1756 |
|
|---|
| 1757 | if (interlace_type == PNG_INTERLACE_ADAM7)
|
|---|
| 1758 | number_of_passes
|
|---|
| 1759 | = png_set_interlace_handling(png_ptr);
|
|---|
| 1760 |
|
|---|
| 1761 | This will return the number of passes needed. Currently, this
|
|---|
| 1762 | is seven, but may change if another interlace type is added.
|
|---|
| 1763 | This function can be called even if the file is not interlaced,
|
|---|
| 1764 | where it will return one pass.
|
|---|
| 1765 |
|
|---|
| 1766 | If you are not going to display the image after each pass, but are
|
|---|
| 1767 | going to wait until the entire image is read in, use the sparkle
|
|---|
| 1768 | effect. This effect is faster and the end result of either method
|
|---|
| 1769 | is exactly the same. If you are planning on displaying the image
|
|---|
| 1770 | after each pass, the "rectangle" effect is generally considered the
|
|---|
| 1771 | better looking one.
|
|---|
| 1772 |
|
|---|
| 1773 | If you only want the "sparkle" effect, just call png_read_rows() as
|
|---|
| 1774 | normal, with the third parameter NULL. Make sure you make pass over
|
|---|
| 1775 | the image number_of_passes times, and you don't change the data in the
|
|---|
| 1776 | rows between calls. You can change the locations of the data, just
|
|---|
| 1777 | not the data. Each pass only writes the pixels appropriate for that
|
|---|
| 1778 | pass, and assumes the data from previous passes is still valid.
|
|---|
| 1779 |
|
|---|
| 1780 | png_read_rows(png_ptr, row_pointers, NULL,
|
|---|
| 1781 | number_of_rows);
|
|---|
| 1782 |
|
|---|
| 1783 | If you only want the first effect (the rectangles), do the same as
|
|---|
| 1784 | before except pass the row buffer in the third parameter, and leave
|
|---|
| 1785 | the second parameter NULL.
|
|---|
| 1786 |
|
|---|
| 1787 | png_read_rows(png_ptr, NULL, row_pointers,
|
|---|
| 1788 | number_of_rows);
|
|---|
| 1789 |
|
|---|
| 1790 | .SS Finishing a sequential read
|
|---|
| 1791 |
|
|---|
| 1792 | After you are finished reading the image through the
|
|---|
| 1793 | low-level interface, you can finish reading the file. If you are
|
|---|
| 1794 | interested in comments or time, which may be stored either before or
|
|---|
| 1795 | after the image data, you should pass the separate png_info struct if
|
|---|
| 1796 | you want to keep the comments from before and after the image
|
|---|
| 1797 | separate. If you are not interested, you can pass NULL.
|
|---|
| 1798 |
|
|---|
| 1799 | png_read_end(png_ptr, end_info);
|
|---|
| 1800 |
|
|---|
| 1801 | When you are done, you can free all memory allocated by libpng like this:
|
|---|
| 1802 |
|
|---|
| 1803 | png_destroy_read_struct(&png_ptr, &info_ptr,
|
|---|
| 1804 | &end_info);
|
|---|
| 1805 |
|
|---|
| 1806 | It is also possible to individually free the info_ptr members that
|
|---|
| 1807 | point to libpng-allocated storage with the following function:
|
|---|
| 1808 |
|
|---|
| 1809 | png_free_data(png_ptr, info_ptr, mask, seq)
|
|---|
| 1810 | mask - identifies data to be freed, a mask
|
|---|
| 1811 | containing the bitwise OR of one or
|
|---|
| 1812 | more of
|
|---|
| 1813 | PNG_FREE_PLTE, PNG_FREE_TRNS,
|
|---|
| 1814 | PNG_FREE_HIST, PNG_FREE_ICCP,
|
|---|
| 1815 | PNG_FREE_PCAL, PNG_FREE_ROWS,
|
|---|
| 1816 | PNG_FREE_SCAL, PNG_FREE_SPLT,
|
|---|
| 1817 | PNG_FREE_TEXT, PNG_FREE_UNKN,
|
|---|
| 1818 | or simply PNG_FREE_ALL
|
|---|
| 1819 | seq - sequence number of item to be freed
|
|---|
| 1820 | (\-1 for all items)
|
|---|
| 1821 |
|
|---|
| 1822 | This function may be safely called when the relevant storage has
|
|---|
| 1823 | already been freed, or has not yet been allocated, or was allocated
|
|---|
| 1824 | by the user and not by libpng, and will in those cases do nothing.
|
|---|
| 1825 | The "seq" parameter is ignored if only one item of the selected data
|
|---|
| 1826 | type, such as PLTE, is allowed. If "seq" is not \-1, and multiple items
|
|---|
| 1827 | are allowed for the data type identified in the mask, such as text or
|
|---|
| 1828 | sPLT, only the n'th item in the structure is freed, where n is "seq".
|
|---|
| 1829 |
|
|---|
| 1830 | The default behavior is only to free data that was allocated internally
|
|---|
| 1831 | by libpng. This can be changed, so that libpng will not free the data,
|
|---|
| 1832 | or so that it will free data that was allocated by the user with png_malloc()
|
|---|
| 1833 | or png_zalloc() and passed in via a png_set_*() function, with
|
|---|
| 1834 |
|
|---|
| 1835 | png_data_freer(png_ptr, info_ptr, freer, mask)
|
|---|
| 1836 | mask - which data elements are affected
|
|---|
| 1837 | same choices as in png_free_data()
|
|---|
| 1838 | freer - one of
|
|---|
| 1839 | PNG_DESTROY_WILL_FREE_DATA
|
|---|
| 1840 | PNG_SET_WILL_FREE_DATA
|
|---|
| 1841 | PNG_USER_WILL_FREE_DATA
|
|---|
| 1842 |
|
|---|
| 1843 | This function only affects data that has already been allocated.
|
|---|
| 1844 | You can call this function after reading the PNG data but before calling
|
|---|
| 1845 | any png_set_*() functions, to control whether the user or the png_set_*()
|
|---|
| 1846 | function is responsible for freeing any existing data that might be present,
|
|---|
| 1847 | and again after the png_set_*() functions to control whether the user
|
|---|
| 1848 | or png_destroy_*() is supposed to free the data. When the user assumes
|
|---|
| 1849 | responsibility for libpng-allocated data, the application must use
|
|---|
| 1850 | png_free() to free it, and when the user transfers responsibility to libpng
|
|---|
| 1851 | for data that the user has allocated, the user must have used png_malloc()
|
|---|
| 1852 | or png_zalloc() to allocate it.
|
|---|
| 1853 |
|
|---|
| 1854 | If you allocated your row_pointers in a single block, as suggested above in
|
|---|
| 1855 | the description of the high level read interface, you must not transfer
|
|---|
| 1856 | responsibility for freeing it to the png_set_rows or png_read_destroy function,
|
|---|
| 1857 | because they would also try to free the individual row_pointers[i].
|
|---|
| 1858 |
|
|---|
| 1859 | If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
|
|---|
| 1860 | separately, do not transfer responsibility for freeing text_ptr to libpng,
|
|---|
| 1861 | because when libpng fills a png_text structure it combines these members with
|
|---|
| 1862 | the key member, and png_free_data() will free only text_ptr.key. Similarly,
|
|---|
| 1863 | if you transfer responsibility for free'ing text_ptr from libpng to your
|
|---|
| 1864 | application, your application must not separately free those members.
|
|---|
| 1865 |
|
|---|
| 1866 | The png_free_data() function will turn off the "valid" flag for anything
|
|---|
| 1867 | it frees. If you need to turn the flag off for a chunk that was freed by
|
|---|
| 1868 | your application instead of by libpng, you can use
|
|---|
| 1869 |
|
|---|
| 1870 | png_set_invalid(png_ptr, info_ptr, mask);
|
|---|
| 1871 | mask - identifies the chunks to be made invalid,
|
|---|
| 1872 | containing the bitwise OR of one or
|
|---|
| 1873 | more of
|
|---|
| 1874 | PNG_INFO_gAMA, PNG_INFO_sBIT,
|
|---|
| 1875 | PNG_INFO_cHRM, PNG_INFO_PLTE,
|
|---|
| 1876 | PNG_INFO_tRNS, PNG_INFO_bKGD,
|
|---|
| 1877 | PNG_INFO_hIST, PNG_INFO_pHYs,
|
|---|
| 1878 | PNG_INFO_oFFs, PNG_INFO_tIME,
|
|---|
| 1879 | PNG_INFO_pCAL, PNG_INFO_sRGB,
|
|---|
| 1880 | PNG_INFO_iCCP, PNG_INFO_sPLT,
|
|---|
| 1881 | PNG_INFO_sCAL, PNG_INFO_IDAT
|
|---|
| 1882 |
|
|---|
| 1883 | For a more compact example of reading a PNG image, see the file example.c.
|
|---|
| 1884 |
|
|---|
| 1885 | .SS Reading PNG files progressively
|
|---|
| 1886 |
|
|---|
| 1887 | The progressive reader is slightly different then the non-progressive
|
|---|
| 1888 | reader. Instead of calling png_read_info(), png_read_rows(), and
|
|---|
| 1889 | png_read_end(), you make one call to png_process_data(), which calls
|
|---|
| 1890 | callbacks when it has the info, a row, or the end of the image. You
|
|---|
| 1891 | set up these callbacks with png_set_progressive_read_fn(). You don't
|
|---|
| 1892 | have to worry about the input/output functions of libpng, as you are
|
|---|
| 1893 | giving the library the data directly in png_process_data(). I will
|
|---|
| 1894 | assume that you have read the section on reading PNG files above,
|
|---|
| 1895 | so I will only highlight the differences (although I will show
|
|---|
| 1896 | all of the code).
|
|---|
| 1897 |
|
|---|
| 1898 | png_structp png_ptr;
|
|---|
| 1899 | png_infop info_ptr;
|
|---|
| 1900 |
|
|---|
| 1901 | /* An example code fragment of how you would
|
|---|
| 1902 | initialize the progressive reader in your
|
|---|
| 1903 | application. */
|
|---|
| 1904 | int
|
|---|
| 1905 | initialize_png_reader()
|
|---|
| 1906 | {
|
|---|
| 1907 | png_ptr = png_create_read_struct
|
|---|
| 1908 | (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
|
|---|
| 1909 | user_error_fn, user_warning_fn);
|
|---|
| 1910 | if (!png_ptr)
|
|---|
| 1911 | return (ERROR);
|
|---|
| 1912 | info_ptr = png_create_info_struct(png_ptr);
|
|---|
| 1913 | if (!info_ptr)
|
|---|
| 1914 | {
|
|---|
| 1915 | png_destroy_read_struct(&png_ptr, (png_infopp)NULL,
|
|---|
| 1916 | (png_infopp)NULL);
|
|---|
| 1917 | return (ERROR);
|
|---|
| 1918 | }
|
|---|
| 1919 |
|
|---|
| 1920 | if (setjmp(png_jmpbuf(png_ptr)))
|
|---|
| 1921 | {
|
|---|
| 1922 | png_destroy_read_struct(&png_ptr, &info_ptr,
|
|---|
| 1923 | (png_infopp)NULL);
|
|---|
| 1924 | return (ERROR);
|
|---|
| 1925 | }
|
|---|
| 1926 |
|
|---|
| 1927 | /* This one's new. You can provide functions
|
|---|
| 1928 | to be called when the header info is valid,
|
|---|
| 1929 | when each row is completed, and when the image
|
|---|
| 1930 | is finished. If you aren't using all functions,
|
|---|
| 1931 | you can specify NULL parameters. Even when all
|
|---|
| 1932 | three functions are NULL, you need to call
|
|---|
| 1933 | png_set_progressive_read_fn(). You can use
|
|---|
| 1934 | any struct as the user_ptr (cast to a void pointer
|
|---|
| 1935 | for the function call), and retrieve the pointer
|
|---|
| 1936 | from inside the callbacks using the function
|
|---|
| 1937 |
|
|---|
| 1938 | png_get_progressive_ptr(png_ptr);
|
|---|
| 1939 |
|
|---|
| 1940 | which will return a void pointer, which you have
|
|---|
| 1941 | to cast appropriately.
|
|---|
| 1942 | */
|
|---|
| 1943 | png_set_progressive_read_fn(png_ptr, (void *)user_ptr,
|
|---|
| 1944 | info_callback, row_callback, end_callback);
|
|---|
| 1945 |
|
|---|
| 1946 | return 0;
|
|---|
| 1947 | }
|
|---|
| 1948 |
|
|---|
| 1949 | /* A code fragment that you call as you receive blocks
|
|---|
| 1950 | of data */
|
|---|
| 1951 | int
|
|---|
| 1952 | process_data(png_bytep buffer, png_uint_32 length)
|
|---|
| 1953 | {
|
|---|
| 1954 | if (setjmp(png_jmpbuf(png_ptr)))
|
|---|
| 1955 | {
|
|---|
| 1956 | png_destroy_read_struct(&png_ptr, &info_ptr,
|
|---|
| 1957 | (png_infopp)NULL);
|
|---|
| 1958 | return (ERROR);
|
|---|
| 1959 | }
|
|---|
| 1960 |
|
|---|
| 1961 | /* This one's new also. Simply give it a chunk
|
|---|
| 1962 | of data from the file stream (in order, of
|
|---|
| 1963 | course). On machines with segmented memory
|
|---|
| 1964 | models machines, don't give it any more than
|
|---|
| 1965 | 64K. The library seems to run fine with sizes
|
|---|
| 1966 | of 4K. Although you can give it much less if
|
|---|
| 1967 | necessary (I assume you can give it chunks of
|
|---|
| 1968 | 1 byte, I haven't tried less then 256 bytes
|
|---|
| 1969 | yet). When this function returns, you may
|
|---|
| 1970 | want to display any rows that were generated
|
|---|
| 1971 | in the row callback if you don't already do
|
|---|
| 1972 | so there.
|
|---|
| 1973 | */
|
|---|
| 1974 | png_process_data(png_ptr, info_ptr, buffer, length);
|
|---|
| 1975 | return 0;
|
|---|
| 1976 | }
|
|---|
| 1977 |
|
|---|
| 1978 | /* This function is called (as set by
|
|---|
| 1979 | png_set_progressive_read_fn() above) when enough data
|
|---|
| 1980 | has been supplied so all of the header has been
|
|---|
| 1981 | read.
|
|---|
| 1982 | */
|
|---|
| 1983 | void
|
|---|
| 1984 | info_callback(png_structp png_ptr, png_infop info)
|
|---|
| 1985 | {
|
|---|
| 1986 | /* Do any setup here, including setting any of
|
|---|
| 1987 | the transformations mentioned in the Reading
|
|---|
| 1988 | PNG files section. For now, you _must_ call
|
|---|
| 1989 | either png_start_read_image() or
|
|---|
| 1990 | png_read_update_info() after all the
|
|---|
| 1991 | transformations are set (even if you don't set
|
|---|
| 1992 | any). You may start getting rows before
|
|---|
| 1993 | png_process_data() returns, so this is your
|
|---|
| 1994 | last chance to prepare for that.
|
|---|
| 1995 | */
|
|---|
| 1996 | }
|
|---|
| 1997 |
|
|---|
| 1998 | /* This function is called when each row of image
|
|---|
| 1999 | data is complete */
|
|---|
| 2000 | void
|
|---|
| 2001 | row_callback(png_structp png_ptr, png_bytep new_row,
|
|---|
| 2002 | png_uint_32 row_num, int pass)
|
|---|
| 2003 | {
|
|---|
| 2004 | /* If the image is interlaced, and you turned
|
|---|
| 2005 | on the interlace handler, this function will
|
|---|
| 2006 | be called for every row in every pass. Some
|
|---|
| 2007 | of these rows will not be changed from the
|
|---|
| 2008 | previous pass. When the row is not changed,
|
|---|
| 2009 | the new_row variable will be NULL. The rows
|
|---|
| 2010 | and passes are called in order, so you don't
|
|---|
| 2011 | really need the row_num and pass, but I'm
|
|---|
| 2012 | supplying them because it may make your life
|
|---|
| 2013 | easier.
|
|---|
| 2014 |
|
|---|
| 2015 | For the non-NULL rows of interlaced images,
|
|---|
| 2016 | you must call png_progressive_combine_row()
|
|---|
| 2017 | passing in the row and the old row. You can
|
|---|
| 2018 | call this function for NULL rows (it will just
|
|---|
| 2019 | return) and for non-interlaced images (it just
|
|---|
| 2020 | does the memcpy for you) if it will make the
|
|---|
| 2021 | code easier. Thus, you can just do this for
|
|---|
| 2022 | all cases:
|
|---|
| 2023 | */
|
|---|
| 2024 |
|
|---|
| 2025 | png_progressive_combine_row(png_ptr, old_row,
|
|---|
| 2026 | new_row);
|
|---|
| 2027 |
|
|---|
| 2028 | /* where old_row is what was displayed for
|
|---|
| 2029 | previously for the row. Note that the first
|
|---|
| 2030 | pass (pass == 0, really) will completely cover
|
|---|
| 2031 | the old row, so the rows do not have to be
|
|---|
| 2032 | initialized. After the first pass (and only
|
|---|
| 2033 | for interlaced images), you will have to pass
|
|---|
| 2034 | the current row, and the function will combine
|
|---|
| 2035 | the old row and the new row.
|
|---|
| 2036 | */
|
|---|
| 2037 | }
|
|---|
| 2038 |
|
|---|
| 2039 | void
|
|---|
| 2040 | end_callback(png_structp png_ptr, png_infop info)
|
|---|
| 2041 | {
|
|---|
| 2042 | /* This function is called after the whole image
|
|---|
| 2043 | has been read, including any chunks after the
|
|---|
| 2044 | image (up to and including the IEND). You
|
|---|
| 2045 | will usually have the same info chunk as you
|
|---|
| 2046 | had in the header, although some data may have
|
|---|
| 2047 | been added to the comments and time fields.
|
|---|
| 2048 |
|
|---|
| 2049 | Most people won't do much here, perhaps setting
|
|---|
| 2050 | a flag that marks the image as finished.
|
|---|
| 2051 | */
|
|---|
| 2052 | }
|
|---|
| 2053 |
|
|---|
| 2054 |
|
|---|
| 2055 |
|
|---|
| 2056 | .SH IV. Writing
|
|---|
| 2057 |
|
|---|
| 2058 | Much of this is very similar to reading. However, everything of
|
|---|
| 2059 | importance is repeated here, so you won't have to constantly look
|
|---|
| 2060 | back up in the reading section to understand writing.
|
|---|
| 2061 |
|
|---|
| 2062 | .SS Setup
|
|---|
| 2063 |
|
|---|
| 2064 | You will want to do the I/O initialization before you get into libpng,
|
|---|
| 2065 | so if it doesn't work, you don't have anything to undo. If you are not
|
|---|
| 2066 | using the standard I/O functions, you will need to replace them with
|
|---|
| 2067 | custom writing functions. See the discussion under Customizing libpng.
|
|---|
| 2068 |
|
|---|
| 2069 | FILE *fp = fopen(file_name, "wb");
|
|---|
| 2070 | if (!fp)
|
|---|
| 2071 | {
|
|---|
| 2072 | return (ERROR);
|
|---|
| 2073 | }
|
|---|
| 2074 |
|
|---|
| 2075 | Next, png_struct and png_info need to be allocated and initialized.
|
|---|
| 2076 | As these can be both relatively large, you may not want to store these
|
|---|
| 2077 | on the stack, unless you have stack space to spare. Of course, you
|
|---|
| 2078 | will want to check if they return NULL. If you are also reading,
|
|---|
| 2079 | you won't want to name your read structure and your write structure
|
|---|
| 2080 | both "png_ptr"; you can call them anything you like, such as
|
|---|
| 2081 | "read_ptr" and "write_ptr". Look at pngtest.c, for example.
|
|---|
| 2082 |
|
|---|
| 2083 | png_structp png_ptr = png_create_write_struct
|
|---|
| 2084 | (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
|
|---|
| 2085 | user_error_fn, user_warning_fn);
|
|---|
| 2086 | if (!png_ptr)
|
|---|
| 2087 | return (ERROR);
|
|---|
| 2088 |
|
|---|
| 2089 | png_infop info_ptr = png_create_info_struct(png_ptr);
|
|---|
| 2090 | if (!info_ptr)
|
|---|
| 2091 | {
|
|---|
| 2092 | png_destroy_write_struct(&png_ptr,
|
|---|
| 2093 | (png_infopp)NULL);
|
|---|
| 2094 | return (ERROR);
|
|---|
| 2095 | }
|
|---|
| 2096 |
|
|---|
| 2097 | If you want to use your own memory allocation routines,
|
|---|
| 2098 | define PNG_USER_MEM_SUPPORTED and use
|
|---|
| 2099 | png_create_write_struct_2() instead of png_create_write_struct():
|
|---|
| 2100 |
|
|---|
| 2101 | png_structp png_ptr = png_create_write_struct_2
|
|---|
| 2102 | (PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
|
|---|
| 2103 | user_error_fn, user_warning_fn, (png_voidp)
|
|---|
| 2104 | user_mem_ptr, user_malloc_fn, user_free_fn);
|
|---|
| 2105 |
|
|---|
| 2106 | After you have these structures, you will need to set up the
|
|---|
| 2107 | error handling. When libpng encounters an error, it expects to
|
|---|
| 2108 | longjmp() back to your routine. Therefore, you will need to call
|
|---|
| 2109 | setjmp() and pass the png_jmpbuf(png_ptr). If you
|
|---|
| 2110 | write the file from different routines, you will need to update
|
|---|
| 2111 | the png_jmpbuf(png_ptr) every time you enter a new routine that will
|
|---|
| 2112 | call a png_*() function. See your documentation of setjmp/longjmp
|
|---|
| 2113 | for your compiler for more information on setjmp/longjmp. See
|
|---|
| 2114 | the discussion on libpng error handling in the Customizing Libpng
|
|---|
| 2115 | section below for more information on the libpng error handling.
|
|---|
| 2116 |
|
|---|
| 2117 | if (setjmp(png_jmpbuf(png_ptr)))
|
|---|
| 2118 | {
|
|---|
| 2119 | png_destroy_write_struct(&png_ptr, &info_ptr);
|
|---|
| 2120 | fclose(fp);
|
|---|
| 2121 | return (ERROR);
|
|---|
| 2122 | }
|
|---|
| 2123 | ...
|
|---|
| 2124 | return;
|
|---|
| 2125 |
|
|---|
| 2126 | If you would rather avoid the complexity of setjmp/longjmp issues,
|
|---|
| 2127 | you can compile libpng with PNG_SETJMP_NOT_SUPPORTED, in which case
|
|---|
| 2128 | errors will result in a call to PNG_ABORT() which defaults to abort().
|
|---|
| 2129 |
|
|---|
| 2130 | Now you need to set up the output code. The default for libpng is to
|
|---|
| 2131 | use the C function fwrite(). If you use this, you will need to pass a
|
|---|
| 2132 | valid FILE * in the function png_init_io(). Be sure that the file is
|
|---|
| 2133 | opened in binary mode. Again, if you wish to handle writing data in
|
|---|
| 2134 | another way, see the discussion on libpng I/O handling in the Customizing
|
|---|
| 2135 | Libpng section below.
|
|---|
| 2136 |
|
|---|
| 2137 | png_init_io(png_ptr, fp);
|
|---|
| 2138 |
|
|---|
| 2139 | If you are embedding your PNG into a datastream such as MNG, and don't
|
|---|
| 2140 | want libpng to write the 8-byte signature, or if you have already
|
|---|
| 2141 | written the signature in your application, use
|
|---|
| 2142 |
|
|---|
| 2143 | png_set_sig_bytes(png_ptr, 8);
|
|---|
| 2144 |
|
|---|
| 2145 | to inform libpng that it should not write a signature.
|
|---|
| 2146 |
|
|---|
| 2147 | .SS Write callbacks
|
|---|
| 2148 |
|
|---|
| 2149 | At this point, you can set up a callback function that will be
|
|---|
| 2150 | called after each row has been written, which you can use to control
|
|---|
| 2151 | a progress meter or the like. It's demonstrated in pngtest.c.
|
|---|
| 2152 | You must supply a function
|
|---|
| 2153 |
|
|---|
| 2154 | void write_row_callback(png_ptr, png_uint_32 row,
|
|---|
| 2155 | int pass);
|
|---|
| 2156 | {
|
|---|
| 2157 | /* put your code here */
|
|---|
| 2158 | }
|
|---|
| 2159 |
|
|---|
| 2160 | (You can give it another name that you like instead of "write_row_callback")
|
|---|
| 2161 |
|
|---|
| 2162 | To inform libpng about your function, use
|
|---|
| 2163 |
|
|---|
| 2164 | png_set_write_status_fn(png_ptr, write_row_callback);
|
|---|
| 2165 |
|
|---|
| 2166 | You now have the option of modifying how the compression library will
|
|---|
| 2167 | run. The following functions are mainly for testing, but may be useful
|
|---|
| 2168 | in some cases, like if you need to write PNG files extremely fast and
|
|---|
| 2169 | are willing to give up some compression, or if you want to get the
|
|---|
| 2170 | maximum possible compression at the expense of slower writing. If you
|
|---|
| 2171 | have no special needs in this area, let the library do what it wants by
|
|---|
| 2172 | not calling this function at all, as it has been tuned to deliver a good
|
|---|
| 2173 | speed/compression ratio. The second parameter to png_set_filter() is
|
|---|
| 2174 | the filter method, for which the only valid values are 0 (as of the
|
|---|
| 2175 | July 1999 PNG specification, version 1.2) or 64 (if you are writing
|
|---|
| 2176 | a PNG datastream that is to be embedded in a MNG datastream). The third
|
|---|
| 2177 | parameter is a flag that indicates which filter type(s) are to be tested
|
|---|
| 2178 | for each scanline. See the PNG specification for details on the specific
|
|---|
| 2179 | filter types.
|
|---|
| 2180 |
|
|---|
| 2181 |
|
|---|
| 2182 | /* turn on or off filtering, and/or choose
|
|---|
| 2183 | specific filters. You can use either a single
|
|---|
| 2184 | PNG_FILTER_VALUE_NAME or the bitwise OR of one
|
|---|
| 2185 | or more PNG_FILTER_NAME masks. */
|
|---|
| 2186 | png_set_filter(png_ptr, 0,
|
|---|
| 2187 | PNG_FILTER_NONE | PNG_FILTER_VALUE_NONE |
|
|---|
| 2188 | PNG_FILTER_SUB | PNG_FILTER_VALUE_SUB |
|
|---|
| 2189 | PNG_FILTER_UP | PNG_FILTER_VALUE_UP |
|
|---|
| 2190 | PNG_FILTER_AVG | PNG_FILTER_VALUE_AVG |
|
|---|
| 2191 | PNG_FILTER_PAETH | PNG_FILTER_VALUE_PAETH|
|
|---|
| 2192 | PNG_ALL_FILTERS);
|
|---|
| 2193 |
|
|---|
| 2194 | If an application
|
|---|
| 2195 | wants to start and stop using particular filters during compression,
|
|---|
| 2196 | it should start out with all of the filters (to ensure that the previous
|
|---|
| 2197 | row of pixels will be stored in case it's needed later), and then add
|
|---|
| 2198 | and remove them after the start of compression.
|
|---|
| 2199 |
|
|---|
| 2200 | If you are writing a PNG datastream that is to be embedded in a MNG
|
|---|
| 2201 | datastream, the second parameter can be either 0 or 64.
|
|---|
| 2202 |
|
|---|
| 2203 | The png_set_compression_*() functions interface to the zlib compression
|
|---|
| 2204 | library, and should mostly be ignored unless you really know what you are
|
|---|
| 2205 | doing. The only generally useful call is png_set_compression_level()
|
|---|
| 2206 | which changes how much time zlib spends on trying to compress the image
|
|---|
| 2207 | data. See the Compression Library (zlib.h and algorithm.txt, distributed
|
|---|
| 2208 | with zlib) for details on the compression levels.
|
|---|
| 2209 |
|
|---|
| 2210 | /* set the zlib compression level */
|
|---|
| 2211 | png_set_compression_level(png_ptr,
|
|---|
| 2212 | Z_BEST_COMPRESSION);
|
|---|
| 2213 |
|
|---|
| 2214 | /* set other zlib parameters */
|
|---|
| 2215 | png_set_compression_mem_level(png_ptr, 8);
|
|---|
| 2216 | png_set_compression_strategy(png_ptr,
|
|---|
| 2217 | Z_DEFAULT_STRATEGY);
|
|---|
| 2218 | png_set_compression_window_bits(png_ptr, 15);
|
|---|
| 2219 | png_set_compression_method(png_ptr, 8);
|
|---|
| 2220 | png_set_compression_buffer_size(png_ptr, 8192)
|
|---|
| 2221 |
|
|---|
| 2222 | extern PNG_EXPORT(void,png_set_zbuf_size)
|
|---|
| 2223 |
|
|---|
| 2224 | .SS Setting the contents of info for output
|
|---|
| 2225 |
|
|---|
| 2226 | You now need to fill in the png_info structure with all the data you
|
|---|
| 2227 | wish to write before the actual image. Note that the only thing you
|
|---|
| 2228 | are allowed to write after the image is the text chunks and the time
|
|---|
| 2229 | chunk (as of PNG Specification 1.2, anyway). See png_write_end() and
|
|---|
| 2230 | the latest PNG specification for more information on that. If you
|
|---|
| 2231 | wish to write them before the image, fill them in now, and flag that
|
|---|
| 2232 | data as being valid. If you want to wait until after the data, don't
|
|---|
| 2233 | fill them until png_write_end(). For all the fields in png_info and
|
|---|
| 2234 | their data types, see png.h. For explanations of what the fields
|
|---|
| 2235 | contain, see the PNG specification.
|
|---|
| 2236 |
|
|---|
| 2237 | Some of the more important parts of the png_info are:
|
|---|
| 2238 |
|
|---|
| 2239 | png_set_IHDR(png_ptr, info_ptr, width, height,
|
|---|
| 2240 | bit_depth, color_type, interlace_type,
|
|---|
| 2241 | compression_type, filter_method)
|
|---|
| 2242 | width - holds the width of the image
|
|---|
| 2243 | in pixels (up to 2^31).
|
|---|
| 2244 | height - holds the height of the image
|
|---|
| 2245 | in pixels (up to 2^31).
|
|---|
| 2246 | bit_depth - holds the bit depth of one of the
|
|---|
| 2247 | image channels.
|
|---|
| 2248 | (valid values are 1, 2, 4, 8, 16
|
|---|
| 2249 | and depend also on the
|
|---|
| 2250 | color_type. See also significant
|
|---|
| 2251 | bits (sBIT) below).
|
|---|
| 2252 | color_type - describes which color/alpha
|
|---|
| 2253 | channels are present.
|
|---|
| 2254 | PNG_COLOR_TYPE_GRAY
|
|---|
| 2255 | (bit depths 1, 2, 4, 8, 16)
|
|---|
| 2256 | PNG_COLOR_TYPE_GRAY_ALPHA
|
|---|
| 2257 | (bit depths 8, 16)
|
|---|
| 2258 | PNG_COLOR_TYPE_PALETTE
|
|---|
| 2259 | (bit depths 1, 2, 4, 8)
|
|---|
| 2260 | PNG_COLOR_TYPE_RGB
|
|---|
| 2261 | (bit_depths 8, 16)
|
|---|
| 2262 | PNG_COLOR_TYPE_RGB_ALPHA
|
|---|
| 2263 | (bit_depths 8, 16)
|
|---|
| 2264 |
|
|---|
| 2265 | PNG_COLOR_MASK_PALETTE
|
|---|
| 2266 | PNG_COLOR_MASK_COLOR
|
|---|
| 2267 | PNG_COLOR_MASK_ALPHA
|
|---|
| 2268 |
|
|---|
| 2269 | interlace_type - PNG_INTERLACE_NONE or
|
|---|
| 2270 | PNG_INTERLACE_ADAM7
|
|---|
| 2271 | compression_type - (must be
|
|---|
| 2272 | PNG_COMPRESSION_TYPE_DEFAULT)
|
|---|
| 2273 | filter_method - (must be PNG_FILTER_TYPE_DEFAULT
|
|---|
| 2274 | or, if you are writing a PNG to
|
|---|
| 2275 | be embedded in a MNG datastream,
|
|---|
| 2276 | can also be
|
|---|
| 2277 | PNG_INTRAPIXEL_DIFFERENCING)
|
|---|
| 2278 |
|
|---|
| 2279 | If you call png_set_IHDR(), the call must appear before any of the
|
|---|
| 2280 | other png_set_*() functions, because they might require access to some of
|
|---|
| 2281 | the IHDR settings. The remaining png_set_*() functions can be called
|
|---|
| 2282 | in any order.
|
|---|
| 2283 |
|
|---|
| 2284 | If you wish, you can reset the compression_type, interlace_type, or
|
|---|
| 2285 | filter_method later by calling png_set_IHDR() again; if you do this, the
|
|---|
| 2286 | width, height, bit_depth, and color_type must be the same in each call.
|
|---|
| 2287 |
|
|---|
| 2288 | png_set_PLTE(png_ptr, info_ptr, palette,
|
|---|
| 2289 | num_palette);
|
|---|
| 2290 | palette - the palette for the file
|
|---|
| 2291 | (array of png_color)
|
|---|
| 2292 | num_palette - number of entries in the palette
|
|---|
| 2293 |
|
|---|
| 2294 | png_set_gAMA(png_ptr, info_ptr, gamma);
|
|---|
| 2295 | gamma - the gamma the image was created
|
|---|
| 2296 | at (PNG_INFO_gAMA)
|
|---|
| 2297 |
|
|---|
| 2298 | png_set_sRGB(png_ptr, info_ptr, srgb_intent);
|
|---|
| 2299 | srgb_intent - the rendering intent
|
|---|
| 2300 | (PNG_INFO_sRGB) The presence of
|
|---|
| 2301 | the sRGB chunk means that the pixel
|
|---|
| 2302 | data is in the sRGB color space.
|
|---|
| 2303 | This chunk also implies specific
|
|---|
| 2304 | values of gAMA and cHRM. Rendering
|
|---|
| 2305 | intent is the CSS-1 property that
|
|---|
| 2306 | has been defined by the International
|
|---|
| 2307 | Color Consortium
|
|---|
| 2308 | (http://www.color.org).
|
|---|
| 2309 | It can be one of
|
|---|
| 2310 | PNG_sRGB_INTENT_SATURATION,
|
|---|
| 2311 | PNG_sRGB_INTENT_PERCEPTUAL,
|
|---|
| 2312 | PNG_sRGB_INTENT_ABSOLUTE, or
|
|---|
| 2313 | PNG_sRGB_INTENT_RELATIVE.
|
|---|
| 2314 |
|
|---|
| 2315 |
|
|---|
| 2316 | png_set_sRGB_gAMA_and_cHRM(png_ptr, info_ptr,
|
|---|
| 2317 | srgb_intent);
|
|---|
| 2318 | srgb_intent - the rendering intent
|
|---|
| 2319 | (PNG_INFO_sRGB) The presence of the
|
|---|
| 2320 | sRGB chunk means that the pixel
|
|---|
| 2321 | data is in the sRGB color space.
|
|---|
| 2322 | This function also causes gAMA and
|
|---|
| 2323 | cHRM chunks with the specific values
|
|---|
| 2324 | that are consistent with sRGB to be
|
|---|
| 2325 | written.
|
|---|
| 2326 |
|
|---|
| 2327 | png_set_iCCP(png_ptr, info_ptr, name, compression_type,
|
|---|
| 2328 | profile, proflen);
|
|---|
| 2329 | name - The profile name.
|
|---|
| 2330 | compression - The compression type; always
|
|---|
| 2331 | PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
|
|---|
| 2332 | You may give NULL to this argument to
|
|---|
| 2333 | ignore it.
|
|---|
| 2334 | profile - International Color Consortium color
|
|---|
| 2335 | profile data. May contain NULs.
|
|---|
| 2336 | proflen - length of profile data in bytes.
|
|---|
| 2337 |
|
|---|
| 2338 | png_set_sBIT(png_ptr, info_ptr, sig_bit);
|
|---|
| 2339 | sig_bit - the number of significant bits for
|
|---|
| 2340 | (PNG_INFO_sBIT) each of the gray, red,
|
|---|
| 2341 | green, and blue channels, whichever are
|
|---|
| 2342 | appropriate for the given color type
|
|---|
| 2343 | (png_color_16)
|
|---|
| 2344 |
|
|---|
| 2345 | png_set_tRNS(png_ptr, info_ptr, trans, num_trans,
|
|---|
| 2346 | trans_values);
|
|---|
| 2347 | trans - array of transparent
|
|---|
| 2348 | entries for palette (PNG_INFO_tRNS)
|
|---|
| 2349 | trans_values - graylevel or color sample values
|
|---|
| 2350 | (in order red, green, blue) of the
|
|---|
| 2351 | single transparent color for
|
|---|
| 2352 | non-paletted images (PNG_INFO_tRNS)
|
|---|
| 2353 | num_trans - number of transparent entries
|
|---|
| 2354 | (PNG_INFO_tRNS)
|
|---|
| 2355 |
|
|---|
| 2356 | png_set_hIST(png_ptr, info_ptr, hist);
|
|---|
| 2357 | (PNG_INFO_hIST)
|
|---|
| 2358 | hist - histogram of palette (array of
|
|---|
| 2359 | png_uint_16)
|
|---|
| 2360 |
|
|---|
| 2361 | png_set_tIME(png_ptr, info_ptr, mod_time);
|
|---|
| 2362 | mod_time - time image was last modified
|
|---|
| 2363 | (PNG_VALID_tIME)
|
|---|
| 2364 |
|
|---|
| 2365 | png_set_bKGD(png_ptr, info_ptr, background);
|
|---|
| 2366 | background - background color (PNG_VALID_bKGD)
|
|---|
| 2367 |
|
|---|
| 2368 | png_set_text(png_ptr, info_ptr, text_ptr, num_text);
|
|---|
| 2369 | text_ptr - array of png_text holding image
|
|---|
| 2370 | comments
|
|---|
| 2371 | text_ptr[i].compression - type of compression used
|
|---|
| 2372 | on "text" PNG_TEXT_COMPRESSION_NONE
|
|---|
| 2373 | PNG_TEXT_COMPRESSION_zTXt
|
|---|
| 2374 | PNG_ITXT_COMPRESSION_NONE
|
|---|
| 2375 | PNG_ITXT_COMPRESSION_zTXt
|
|---|
| 2376 | text_ptr[i].key - keyword for comment. Must contain
|
|---|
| 2377 | 1-79 characters.
|
|---|
| 2378 | text_ptr[i].text - text comments for current
|
|---|
| 2379 | keyword. Can be NULL or empty.
|
|---|
| 2380 | text_ptr[i].text_length - length of text string,
|
|---|
| 2381 | after decompression, 0 for iTXt
|
|---|
| 2382 | text_ptr[i].itxt_length - length of itxt string,
|
|---|
| 2383 | after decompression, 0 for tEXt/zTXt
|
|---|
| 2384 | text_ptr[i].lang - language of comment (NULL or
|
|---|
| 2385 | empty for unknown).
|
|---|
| 2386 | text_ptr[i].translated_keyword - keyword in UTF-8 (NULL
|
|---|
| 2387 | or empty for unknown).
|
|---|
| 2388 | Note that the itxt_length, lang, and lang_key
|
|---|
| 2389 | members of the text_ptr structure only exist
|
|---|
| 2390 | when the library is built with iTXt chunk support.
|
|---|
| 2391 |
|
|---|
| 2392 | num_text - number of comments
|
|---|
| 2393 |
|
|---|
| 2394 | png_set_sPLT(png_ptr, info_ptr, &palette_ptr,
|
|---|
| 2395 | num_spalettes);
|
|---|
| 2396 | palette_ptr - array of png_sPLT_struct structures
|
|---|
| 2397 | to be added to the list of palettes
|
|---|
| 2398 | in the info structure.
|
|---|
| 2399 | num_spalettes - number of palette structures to be
|
|---|
| 2400 | added.
|
|---|
| 2401 |
|
|---|
| 2402 | png_set_oFFs(png_ptr, info_ptr, offset_x, offset_y,
|
|---|
| 2403 | unit_type);
|
|---|
| 2404 | offset_x - positive offset from the left
|
|---|
| 2405 | edge of the screen
|
|---|
| 2406 | offset_y - positive offset from the top
|
|---|
| 2407 | edge of the screen
|
|---|
| 2408 | unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
|
|---|
| 2409 |
|
|---|
| 2410 | png_set_pHYs(png_ptr, info_ptr, res_x, res_y,
|
|---|
| 2411 | unit_type);
|
|---|
| 2412 | res_x - pixels/unit physical resolution
|
|---|
| 2413 | in x direction
|
|---|
| 2414 | res_y - pixels/unit physical resolution
|
|---|
| 2415 | in y direction
|
|---|
| 2416 | unit_type - PNG_RESOLUTION_UNKNOWN,
|
|---|
| 2417 | PNG_RESOLUTION_METER
|
|---|
| 2418 |
|
|---|
| 2419 | png_set_sCAL(png_ptr, info_ptr, unit, width, height)
|
|---|
| 2420 | unit - physical scale units (an integer)
|
|---|
| 2421 | width - width of a pixel in physical scale units
|
|---|
| 2422 | height - height of a pixel in physical scale units
|
|---|
| 2423 | (width and height are doubles)
|
|---|
| 2424 |
|
|---|
| 2425 | png_set_sCAL_s(png_ptr, info_ptr, unit, width, height)
|
|---|
| 2426 | unit - physical scale units (an integer)
|
|---|
| 2427 | width - width of a pixel in physical scale units
|
|---|
| 2428 | height - height of a pixel in physical scale units
|
|---|
| 2429 | (width and height are strings like "2.54")
|
|---|
| 2430 |
|
|---|
| 2431 | png_set_unknown_chunks(png_ptr, info_ptr, &unknowns,
|
|---|
| 2432 | num_unknowns)
|
|---|
| 2433 | unknowns - array of png_unknown_chunk
|
|---|
| 2434 | structures holding unknown chunks
|
|---|
| 2435 | unknowns[i].name - name of unknown chunk
|
|---|
| 2436 | unknowns[i].data - data of unknown chunk
|
|---|
| 2437 | unknowns[i].size - size of unknown chunk's data
|
|---|
| 2438 | unknowns[i].location - position to write chunk in file
|
|---|
| 2439 | 0: do not write chunk
|
|---|
| 2440 | PNG_HAVE_IHDR: before PLTE
|
|---|
| 2441 | PNG_HAVE_PLTE: before IDAT
|
|---|
| 2442 | PNG_AFTER_IDAT: after IDAT
|
|---|
| 2443 |
|
|---|
| 2444 | The "location" member is set automatically according to
|
|---|
| 2445 | what part of the output file has already been written.
|
|---|
| 2446 | You can change its value after calling png_set_unknown_chunks()
|
|---|
| 2447 | as demonstrated in pngtest.c. Within each of the "locations",
|
|---|
| 2448 | the chunks are sequenced according to their position in the
|
|---|
| 2449 | structure (that is, the value of "i", which is the order in which
|
|---|
| 2450 | the chunk was either read from the input file or defined with
|
|---|
| 2451 | png_set_unknown_chunks).
|
|---|
| 2452 |
|
|---|
| 2453 | A quick word about text and num_text. text is an array of png_text
|
|---|
| 2454 | structures. num_text is the number of valid structures in the array.
|
|---|
| 2455 | Each png_text structure holds a language code, a keyword, a text value,
|
|---|
| 2456 | and a compression type.
|
|---|
| 2457 |
|
|---|
| 2458 | The compression types have the same valid numbers as the compression
|
|---|
| 2459 | types of the image data. Currently, the only valid number is zero.
|
|---|
| 2460 | However, you can store text either compressed or uncompressed, unlike
|
|---|
| 2461 | images, which always have to be compressed. So if you don't want the
|
|---|
| 2462 | text compressed, set the compression type to PNG_TEXT_COMPRESSION_NONE.
|
|---|
| 2463 | Because tEXt and zTXt chunks don't have a language field, if you
|
|---|
| 2464 | specify PNG_TEXT_COMPRESSION_NONE or PNG_TEXT_COMPRESSION_zTXt
|
|---|
| 2465 | any language code or translated keyword will not be written out.
|
|---|
| 2466 |
|
|---|
| 2467 | Until text gets around 1000 bytes, it is not worth compressing it.
|
|---|
| 2468 | After the text has been written out to the file, the compression type
|
|---|
| 2469 | is set to PNG_TEXT_COMPRESSION_NONE_WR or PNG_TEXT_COMPRESSION_zTXt_WR,
|
|---|
| 2470 | so that it isn't written out again at the end (in case you are calling
|
|---|
| 2471 | png_write_end() with the same struct.
|
|---|
| 2472 |
|
|---|
| 2473 | The keywords that are given in the PNG Specification are:
|
|---|
| 2474 |
|
|---|
| 2475 | Title Short (one line) title or
|
|---|
| 2476 | caption for image
|
|---|
| 2477 | Author Name of image's creator
|
|---|
| 2478 | Description Description of image (possibly long)
|
|---|
| 2479 | Copyright Copyright notice
|
|---|
| 2480 | Creation Time Time of original image creation
|
|---|
| 2481 | (usually RFC 1123 format, see below)
|
|---|
| 2482 | Software Software used to create the image
|
|---|
| 2483 | Disclaimer Legal disclaimer
|
|---|
| 2484 | Warning Warning of nature of content
|
|---|
| 2485 | Source Device used to create the image
|
|---|
| 2486 | Comment Miscellaneous comment; conversion
|
|---|
| 2487 | from other image format
|
|---|
| 2488 |
|
|---|
| 2489 | The keyword-text pairs work like this. Keywords should be short
|
|---|
| 2490 | simple descriptions of what the comment is about. Some typical
|
|---|
| 2491 | keywords are found in the PNG specification, as is some recommendations
|
|---|
| 2492 | on keywords. You can repeat keywords in a file. You can even write
|
|---|
| 2493 | some text before the image and some after. For example, you may want
|
|---|
| 2494 | to put a description of the image before the image, but leave the
|
|---|
| 2495 | disclaimer until after, so viewers working over modem connections
|
|---|
| 2496 | don't have to wait for the disclaimer to go over the modem before
|
|---|
| 2497 | they start seeing the image. Finally, keywords should be full
|
|---|
| 2498 | words, not abbreviations. Keywords and text are in the ISO 8859-1
|
|---|
| 2499 | (Latin-1) character set (a superset of regular ASCII) and can not
|
|---|
| 2500 | contain NUL characters, and should not contain control or other
|
|---|
| 2501 | unprintable characters. To make the comments widely readable, stick
|
|---|
| 2502 | with basic ASCII, and avoid machine specific character set extensions
|
|---|
| 2503 | like the IBM-PC character set. The keyword must be present, but
|
|---|
| 2504 | you can leave off the text string on non-compressed pairs.
|
|---|
| 2505 | Compressed pairs must have a text string, as only the text string
|
|---|
| 2506 | is compressed anyway, so the compression would be meaningless.
|
|---|
| 2507 |
|
|---|
| 2508 | PNG supports modification time via the png_time structure. Two
|
|---|
| 2509 | conversion routines are provided, png_convert_from_time_t() for
|
|---|
| 2510 | time_t and png_convert_from_struct_tm() for struct tm. The
|
|---|
| 2511 | time_t routine uses gmtime(). You don't have to use either of
|
|---|
| 2512 | these, but if you wish to fill in the png_time structure directly,
|
|---|
| 2513 | you should provide the time in universal time (GMT) if possible
|
|---|
| 2514 | instead of your local time. Note that the year number is the full
|
|---|
| 2515 | year (e.g. 1998, rather than 98 - PNG is year 2000 compliant!), and
|
|---|
| 2516 | that months start with 1.
|
|---|
| 2517 |
|
|---|
| 2518 | If you want to store the time of the original image creation, you should
|
|---|
| 2519 | use a plain tEXt chunk with the "Creation Time" keyword. This is
|
|---|
| 2520 | necessary because the "creation time" of a PNG image is somewhat vague,
|
|---|
| 2521 | depending on whether you mean the PNG file, the time the image was
|
|---|
| 2522 | created in a non-PNG format, a still photo from which the image was
|
|---|
| 2523 | scanned, or possibly the subject matter itself. In order to facilitate
|
|---|
| 2524 | machine-readable dates, it is recommended that the "Creation Time"
|
|---|
| 2525 | tEXt chunk use RFC 1123 format dates (e.g. "22 May 1997 18:07:10 GMT"),
|
|---|
| 2526 | although this isn't a requirement. Unlike the tIME chunk, the
|
|---|
| 2527 | "Creation Time" tEXt chunk is not expected to be automatically changed
|
|---|
| 2528 | by the software. To facilitate the use of RFC 1123 dates, a function
|
|---|
| 2529 | png_convert_to_rfc1123(png_timep) is provided to convert from PNG
|
|---|
| 2530 | time to an RFC 1123 format string.
|
|---|
| 2531 |
|
|---|
| 2532 | .SS Writing unknown chunks
|
|---|
| 2533 |
|
|---|
| 2534 | You can use the png_set_unknown_chunks function to queue up chunks
|
|---|
| 2535 | for writing. You give it a chunk name, raw data, and a size; that's
|
|---|
| 2536 | all there is to it. The chunks will be written by the next following
|
|---|
| 2537 | png_write_info_before_PLTE, png_write_info, or png_write_end function.
|
|---|
| 2538 | Any chunks previously read into the info structure's unknown-chunk
|
|---|
| 2539 | list will also be written out in a sequence that satisfies the PNG
|
|---|
| 2540 | specification's ordering rules.
|
|---|
| 2541 |
|
|---|
| 2542 | .SS The high-level write interface
|
|---|
| 2543 |
|
|---|
| 2544 | At this point there are two ways to proceed; through the high-level
|
|---|
| 2545 | write interface, or through a sequence of low-level write operations.
|
|---|
| 2546 | You can use the high-level interface if your image data is present
|
|---|
| 2547 | in the info structure. All defined output
|
|---|
| 2548 | transformations are permitted, enabled by the following masks.
|
|---|
| 2549 |
|
|---|
| 2550 | PNG_TRANSFORM_IDENTITY No transformation
|
|---|
| 2551 | PNG_TRANSFORM_PACKING Pack 1, 2 and 4-bit samples
|
|---|
| 2552 | PNG_TRANSFORM_PACKSWAP Change order of packed
|
|---|
| 2553 | pixels to LSB first
|
|---|
| 2554 | PNG_TRANSFORM_INVERT_MONO Invert monochrome images
|
|---|
| 2555 | PNG_TRANSFORM_SHIFT Normalize pixels to the
|
|---|
| 2556 | sBIT depth
|
|---|
| 2557 | PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
|
|---|
| 2558 | to BGRA
|
|---|
| 2559 | PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
|
|---|
| 2560 | to AG
|
|---|
| 2561 | PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
|
|---|
| 2562 | to transparency
|
|---|
| 2563 | PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
|
|---|
| 2564 | PNG_TRANSFORM_STRIP_FILLER Strip out filler
|
|---|
| 2565 | bytes (deprecated).
|
|---|
| 2566 | PNG_TRANSFORM_STRIP_FILLER_BEFORE Strip out leading
|
|---|
| 2567 | filler bytes
|
|---|
| 2568 | PNG_TRANSFORM_STRIP_FILLER_AFTER Strip out trailing
|
|---|
| 2569 | filler bytes
|
|---|
| 2570 |
|
|---|
| 2571 | If you have valid image data in the info structure (you can use
|
|---|
| 2572 | png_set_rows() to put image data in the info structure), simply do this:
|
|---|
| 2573 |
|
|---|
| 2574 | png_write_png(png_ptr, info_ptr, png_transforms, NULL)
|
|---|
| 2575 |
|
|---|
| 2576 | where png_transforms is an integer containing the bitwise OR of some set of
|
|---|
| 2577 | transformation flags. This call is equivalent to png_write_info(),
|
|---|
| 2578 | followed the set of transformations indicated by the transform mask,
|
|---|
| 2579 | then png_write_image(), and finally png_write_end().
|
|---|
| 2580 |
|
|---|
| 2581 | (The final parameter of this call is not yet used. Someday it might point
|
|---|
| 2582 | to transformation parameters required by some future output transform.)
|
|---|
| 2583 |
|
|---|
| 2584 | You must use png_transforms and not call any png_set_transform() functions
|
|---|
| 2585 | when you use png_write_png().
|
|---|
| 2586 |
|
|---|
| 2587 | .SS The low-level write interface
|
|---|
| 2588 |
|
|---|
| 2589 | If you are going the low-level route instead, you are now ready to
|
|---|
| 2590 | write all the file information up to the actual image data. You do
|
|---|
| 2591 | this with a call to png_write_info().
|
|---|
| 2592 |
|
|---|
| 2593 | png_write_info(png_ptr, info_ptr);
|
|---|
| 2594 |
|
|---|
| 2595 | Note that there is one transformation you may need to do before
|
|---|
| 2596 | png_write_info(). In PNG files, the alpha channel in an image is the
|
|---|
| 2597 | level of opacity. If your data is supplied as a level of transparency,
|
|---|
| 2598 | you can invert the alpha channel before you write it, so that 0 is
|
|---|
| 2599 | fully transparent and 255 (in 8-bit or paletted images) or 65535
|
|---|
| 2600 | (in 16-bit images) is fully opaque, with
|
|---|
| 2601 |
|
|---|
| 2602 | png_set_invert_alpha(png_ptr);
|
|---|
| 2603 |
|
|---|
| 2604 | This must appear before png_write_info() instead of later with the
|
|---|
| 2605 | other transformations because in the case of paletted images the tRNS
|
|---|
| 2606 | chunk data has to be inverted before the tRNS chunk is written. If
|
|---|
| 2607 | your image is not a paletted image, the tRNS data (which in such cases
|
|---|
| 2608 | represents a single color to be rendered as transparent) won't need to
|
|---|
| 2609 | be changed, and you can safely do this transformation after your
|
|---|
| 2610 | png_write_info() call.
|
|---|
| 2611 |
|
|---|
| 2612 | If you need to write a private chunk that you want to appear before
|
|---|
| 2613 | the PLTE chunk when PLTE is present, you can write the PNG info in
|
|---|
| 2614 | two steps, and insert code to write your own chunk between them:
|
|---|
| 2615 |
|
|---|
| 2616 | png_write_info_before_PLTE(png_ptr, info_ptr);
|
|---|
| 2617 | png_set_unknown_chunks(png_ptr, info_ptr, ...);
|
|---|
| 2618 | png_write_info(png_ptr, info_ptr);
|
|---|
| 2619 |
|
|---|
| 2620 | After you've written the file information, you can set up the library
|
|---|
| 2621 | to handle any special transformations of the image data. The various
|
|---|
| 2622 | ways to transform the data will be described in the order that they
|
|---|
| 2623 | should occur. This is important, as some of these change the color
|
|---|
| 2624 | type and/or bit depth of the data, and some others only work on
|
|---|
| 2625 | certain color types and bit depths. Even though each transformation
|
|---|
| 2626 | checks to see if it has data that it can do something with, you should
|
|---|
| 2627 | make sure to only enable a transformation if it will be valid for the
|
|---|
| 2628 | data. For example, don't swap red and blue on grayscale data.
|
|---|
| 2629 |
|
|---|
| 2630 | PNG files store RGB pixels packed into 3 or 6 bytes. This code tells
|
|---|
| 2631 | the library to strip input data that has 4 or 8 bytes per pixel down
|
|---|
| 2632 | to 3 or 6 bytes (or strip 2 or 4-byte grayscale+filler data to 1 or 2
|
|---|
| 2633 | bytes per pixel).
|
|---|
| 2634 |
|
|---|
| 2635 | png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE);
|
|---|
| 2636 |
|
|---|
| 2637 | where the 0 is unused, and the location is either PNG_FILLER_BEFORE or
|
|---|
| 2638 | PNG_FILLER_AFTER, depending upon whether the filler byte in the pixel
|
|---|
| 2639 | is stored XRGB or RGBX.
|
|---|
| 2640 |
|
|---|
| 2641 | PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
|
|---|
| 2642 | they can, resulting in, for example, 8 pixels per byte for 1 bit files.
|
|---|
| 2643 | If the data is supplied at 1 pixel per byte, use this code, which will
|
|---|
| 2644 | correctly pack the pixels into a single byte:
|
|---|
| 2645 |
|
|---|
| 2646 | png_set_packing(png_ptr);
|
|---|
| 2647 |
|
|---|
| 2648 | PNG files reduce possible bit depths to 1, 2, 4, 8, and 16. If your
|
|---|
| 2649 | data is of another bit depth, you can write an sBIT chunk into the
|
|---|
| 2650 | file so that decoders can recover the original data if desired.
|
|---|
| 2651 |
|
|---|
| 2652 | /* Set the true bit depth of the image data */
|
|---|
| 2653 | if (color_type & PNG_COLOR_MASK_COLOR)
|
|---|
| 2654 | {
|
|---|
| 2655 | sig_bit.red = true_bit_depth;
|
|---|
| 2656 | sig_bit.green = true_bit_depth;
|
|---|
| 2657 | sig_bit.blue = true_bit_depth;
|
|---|
| 2658 | }
|
|---|
| 2659 | else
|
|---|
| 2660 | {
|
|---|
| 2661 | sig_bit.gray = true_bit_depth;
|
|---|
| 2662 | }
|
|---|
| 2663 | if (color_type & PNG_COLOR_MASK_ALPHA)
|
|---|
| 2664 | {
|
|---|
| 2665 | sig_bit.alpha = true_bit_depth;
|
|---|
| 2666 | }
|
|---|
| 2667 |
|
|---|
| 2668 | png_set_sBIT(png_ptr, info_ptr, &sig_bit);
|
|---|
| 2669 |
|
|---|
| 2670 | If the data is stored in the row buffer in a bit depth other than
|
|---|
| 2671 | one supported by PNG (e.g. 3 bit data in the range 0-7 for a 4-bit PNG),
|
|---|
| 2672 | this will scale the values to appear to be the correct bit depth as
|
|---|
| 2673 | is required by PNG.
|
|---|
| 2674 |
|
|---|
| 2675 | png_set_shift(png_ptr, &sig_bit);
|
|---|
| 2676 |
|
|---|
| 2677 | PNG files store 16 bit pixels in network byte order (big-endian,
|
|---|
| 2678 | ie. most significant bits first). This code would be used if they are
|
|---|
| 2679 | supplied the other way (little-endian, i.e. least significant bits
|
|---|
| 2680 | first, the way PCs store them):
|
|---|
| 2681 |
|
|---|
| 2682 | if (bit_depth > 8)
|
|---|
| 2683 | png_set_swap(png_ptr);
|
|---|
| 2684 |
|
|---|
| 2685 | If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
|
|---|
| 2686 | need to change the order the pixels are packed into bytes, you can use:
|
|---|
| 2687 |
|
|---|
| 2688 | if (bit_depth < 8)
|
|---|
| 2689 | png_set_packswap(png_ptr);
|
|---|
| 2690 |
|
|---|
| 2691 | PNG files store 3 color pixels in red, green, blue order. This code
|
|---|
| 2692 | would be used if they are supplied as blue, green, red:
|
|---|
| 2693 |
|
|---|
| 2694 | png_set_bgr(png_ptr);
|
|---|
| 2695 |
|
|---|
| 2696 | PNG files describe monochrome as black being zero and white being
|
|---|
| 2697 | one. This code would be used if the pixels are supplied with this reversed
|
|---|
| 2698 | (black being one and white being zero):
|
|---|
| 2699 |
|
|---|
| 2700 | png_set_invert_mono(png_ptr);
|
|---|
| 2701 |
|
|---|
| 2702 | Finally, you can write your own transformation function if none of
|
|---|
| 2703 | the existing ones meets your needs. This is done by setting a callback
|
|---|
| 2704 | with
|
|---|
| 2705 |
|
|---|
| 2706 | png_set_write_user_transform_fn(png_ptr,
|
|---|
| 2707 | write_transform_fn);
|
|---|
| 2708 |
|
|---|
| 2709 | You must supply the function
|
|---|
| 2710 |
|
|---|
| 2711 | void write_transform_fn(png_ptr ptr, row_info_ptr
|
|---|
| 2712 | row_info, png_bytep data)
|
|---|
| 2713 |
|
|---|
| 2714 | See pngtest.c for a working example. Your function will be called
|
|---|
| 2715 | before any of the other transformations are processed.
|
|---|
| 2716 |
|
|---|
| 2717 | You can also set up a pointer to a user structure for use by your
|
|---|
| 2718 | callback function.
|
|---|
| 2719 |
|
|---|
| 2720 | png_set_user_transform_info(png_ptr, user_ptr, 0, 0);
|
|---|
| 2721 |
|
|---|
| 2722 | The user_channels and user_depth parameters of this function are ignored
|
|---|
| 2723 | when writing; you can set them to zero as shown.
|
|---|
| 2724 |
|
|---|
| 2725 | You can retrieve the pointer via the function png_get_user_transform_ptr().
|
|---|
| 2726 | For example:
|
|---|
| 2727 |
|
|---|
| 2728 | voidp write_user_transform_ptr =
|
|---|
| 2729 | png_get_user_transform_ptr(png_ptr);
|
|---|
| 2730 |
|
|---|
| 2731 | It is possible to have libpng flush any pending output, either manually,
|
|---|
| 2732 | or automatically after a certain number of lines have been written. To
|
|---|
| 2733 | flush the output stream a single time call:
|
|---|
| 2734 |
|
|---|
| 2735 | png_write_flush(png_ptr);
|
|---|
| 2736 |
|
|---|
| 2737 | and to have libpng flush the output stream periodically after a certain
|
|---|
| 2738 | number of scanlines have been written, call:
|
|---|
| 2739 |
|
|---|
| 2740 | png_set_flush(png_ptr, nrows);
|
|---|
| 2741 |
|
|---|
| 2742 | Note that the distance between rows is from the last time png_write_flush()
|
|---|
| 2743 | was called, or the first row of the image if it has never been called.
|
|---|
| 2744 | So if you write 50 lines, and then png_set_flush 25, it will flush the
|
|---|
| 2745 | output on the next scanline, and every 25 lines thereafter, unless
|
|---|
| 2746 | png_write_flush() is called before 25 more lines have been written.
|
|---|
| 2747 | If nrows is too small (less than about 10 lines for a 640 pixel wide
|
|---|
| 2748 | RGB image) the image compression may decrease noticeably (although this
|
|---|
| 2749 | may be acceptable for real-time applications). Infrequent flushing will
|
|---|
| 2750 | only degrade the compression performance by a few percent over images
|
|---|
| 2751 | that do not use flushing.
|
|---|
| 2752 |
|
|---|
| 2753 | .SS Writing the image data
|
|---|
| 2754 |
|
|---|
| 2755 | That's it for the transformations. Now you can write the image data.
|
|---|
| 2756 | The simplest way to do this is in one function call. If you have the
|
|---|
| 2757 | whole image in memory, you can just call png_write_image() and libpng
|
|---|
| 2758 | will write the image. You will need to pass in an array of pointers to
|
|---|
| 2759 | each row. This function automatically handles interlacing, so you don't
|
|---|
| 2760 | need to call png_set_interlace_handling() or call this function multiple
|
|---|
| 2761 | times, or any of that other stuff necessary with png_write_rows().
|
|---|
| 2762 |
|
|---|
| 2763 | png_write_image(png_ptr, row_pointers);
|
|---|
| 2764 |
|
|---|
| 2765 | where row_pointers is:
|
|---|
| 2766 |
|
|---|
| 2767 | png_byte *row_pointers[height];
|
|---|
| 2768 |
|
|---|
| 2769 | You can point to void or char or whatever you use for pixels.
|
|---|
| 2770 |
|
|---|
| 2771 | If you don't want to write the whole image at once, you can
|
|---|
| 2772 | use png_write_rows() instead. If the file is not interlaced,
|
|---|
| 2773 | this is simple:
|
|---|
| 2774 |
|
|---|
| 2775 | png_write_rows(png_ptr, row_pointers,
|
|---|
| 2776 | number_of_rows);
|
|---|
| 2777 |
|
|---|
| 2778 | row_pointers is the same as in the png_write_image() call.
|
|---|
| 2779 |
|
|---|
| 2780 | If you are just writing one row at a time, you can do this with
|
|---|
| 2781 | a single row_pointer instead of an array of row_pointers:
|
|---|
| 2782 |
|
|---|
| 2783 | png_bytep row_pointer = row;
|
|---|
| 2784 |
|
|---|
| 2785 | png_write_row(png_ptr, row_pointer);
|
|---|
| 2786 |
|
|---|
| 2787 | When the file is interlaced, things can get a good deal more complicated.
|
|---|
| 2788 | The only currently (as of the PNG Specification version 1.2, dated July
|
|---|
| 2789 | 1999) defined interlacing scheme for PNG files is the "Adam7" interlace
|
|---|
| 2790 | scheme, that breaks down an image into seven smaller images of varying
|
|---|
| 2791 | size. libpng will build these images for you, or you can do them
|
|---|
| 2792 | yourself. If you want to build them yourself, see the PNG specification
|
|---|
| 2793 | for details of which pixels to write when.
|
|---|
| 2794 |
|
|---|
| 2795 | If you don't want libpng to handle the interlacing details, just
|
|---|
| 2796 | use png_set_interlace_handling() and call png_write_rows() the
|
|---|
| 2797 | correct number of times to write all seven sub-images.
|
|---|
| 2798 |
|
|---|
| 2799 | If you want libpng to build the sub-images, call this before you start
|
|---|
| 2800 | writing any rows:
|
|---|
| 2801 |
|
|---|
| 2802 | number_of_passes =
|
|---|
| 2803 | png_set_interlace_handling(png_ptr);
|
|---|
| 2804 |
|
|---|
| 2805 | This will return the number of passes needed. Currently, this is seven,
|
|---|
| 2806 | but may change if another interlace type is added.
|
|---|
| 2807 |
|
|---|
| 2808 | Then write the complete image number_of_passes times.
|
|---|
| 2809 |
|
|---|
| 2810 | png_write_rows(png_ptr, row_pointers,
|
|---|
| 2811 | number_of_rows);
|
|---|
| 2812 |
|
|---|
| 2813 | As some of these rows are not used, and thus return immediately, you may
|
|---|
| 2814 | want to read about interlacing in the PNG specification, and only update
|
|---|
| 2815 | the rows that are actually used.
|
|---|
| 2816 |
|
|---|
| 2817 | .SS Finishing a sequential write
|
|---|
| 2818 |
|
|---|
| 2819 | After you are finished writing the image, you should finish writing
|
|---|
| 2820 | the file. If you are interested in writing comments or time, you should
|
|---|
| 2821 | pass an appropriately filled png_info pointer. If you are not interested,
|
|---|
| 2822 | you can pass NULL.
|
|---|
| 2823 |
|
|---|
| 2824 | png_write_end(png_ptr, info_ptr);
|
|---|
| 2825 |
|
|---|
| 2826 | When you are done, you can free all memory used by libpng like this:
|
|---|
| 2827 |
|
|---|
| 2828 | png_destroy_write_struct(&png_ptr, &info_ptr);
|
|---|
| 2829 |
|
|---|
| 2830 | It is also possible to individually free the info_ptr members that
|
|---|
| 2831 | point to libpng-allocated storage with the following function:
|
|---|
| 2832 |
|
|---|
| 2833 | png_free_data(png_ptr, info_ptr, mask, seq)
|
|---|
| 2834 | mask - identifies data to be freed, a mask
|
|---|
| 2835 | containing the bitwise OR of one or
|
|---|
| 2836 | more of
|
|---|
| 2837 | PNG_FREE_PLTE, PNG_FREE_TRNS,
|
|---|
| 2838 | PNG_FREE_HIST, PNG_FREE_ICCP,
|
|---|
| 2839 | PNG_FREE_PCAL, PNG_FREE_ROWS,
|
|---|
| 2840 | PNG_FREE_SCAL, PNG_FREE_SPLT,
|
|---|
| 2841 | PNG_FREE_TEXT, PNG_FREE_UNKN,
|
|---|
| 2842 | or simply PNG_FREE_ALL
|
|---|
| 2843 | seq - sequence number of item to be freed
|
|---|
| 2844 | (\-1 for all items)
|
|---|
| 2845 |
|
|---|
| 2846 | This function may be safely called when the relevant storage has
|
|---|
| 2847 | already been freed, or has not yet been allocated, or was allocated
|
|---|
| 2848 | by the user and not by libpng, and will in those cases do nothing.
|
|---|
| 2849 | The "seq" parameter is ignored if only one item of the selected data
|
|---|
| 2850 | type, such as PLTE, is allowed. If "seq" is not \-1, and multiple items
|
|---|
| 2851 | are allowed for the data type identified in the mask, such as text or
|
|---|
| 2852 | sPLT, only the n'th item in the structure is freed, where n is "seq".
|
|---|
| 2853 |
|
|---|
| 2854 | If you allocated data such as a palette that you passed in to libpng
|
|---|
| 2855 | with png_set_*, you must not free it until just before the call to
|
|---|
| 2856 | png_destroy_write_struct().
|
|---|
| 2857 |
|
|---|
| 2858 | The default behavior is only to free data that was allocated internally
|
|---|
| 2859 | by libpng. This can be changed, so that libpng will not free the data,
|
|---|
| 2860 | or so that it will free data that was allocated by the user with png_malloc()
|
|---|
| 2861 | or png_zalloc() and passed in via a png_set_*() function, with
|
|---|
| 2862 |
|
|---|
| 2863 | png_data_freer(png_ptr, info_ptr, freer, mask)
|
|---|
| 2864 | mask - which data elements are affected
|
|---|
| 2865 | same choices as in png_free_data()
|
|---|
| 2866 | freer - one of
|
|---|
| 2867 | PNG_DESTROY_WILL_FREE_DATA
|
|---|
| 2868 | PNG_SET_WILL_FREE_DATA
|
|---|
| 2869 | PNG_USER_WILL_FREE_DATA
|
|---|
| 2870 |
|
|---|
| 2871 | For example, to transfer responsibility for some data from a read structure
|
|---|
| 2872 | to a write structure, you could use
|
|---|
| 2873 |
|
|---|
| 2874 | png_data_freer(read_ptr, read_info_ptr,
|
|---|
| 2875 | PNG_USER_WILL_FREE_DATA,
|
|---|
| 2876 | PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
|
|---|
| 2877 | png_data_freer(write_ptr, write_info_ptr,
|
|---|
| 2878 | PNG_DESTROY_WILL_FREE_DATA,
|
|---|
| 2879 | PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
|
|---|
| 2880 |
|
|---|
| 2881 | thereby briefly reassigning responsibility for freeing to the user but
|
|---|
| 2882 | immediately afterwards reassigning it once more to the write_destroy
|
|---|
| 2883 | function. Having done this, it would then be safe to destroy the read
|
|---|
| 2884 | structure and continue to use the PLTE, tRNS, and hIST data in the write
|
|---|
| 2885 | structure.
|
|---|
| 2886 |
|
|---|
| 2887 | This function only affects data that has already been allocated.
|
|---|
| 2888 | You can call this function before calling after the png_set_*() functions
|
|---|
| 2889 | to control whether the user or png_destroy_*() is supposed to free the data.
|
|---|
| 2890 | When the user assumes responsibility for libpng-allocated data, the
|
|---|
| 2891 | application must use
|
|---|
| 2892 | png_free() to free it, and when the user transfers responsibility to libpng
|
|---|
| 2893 | for data that the user has allocated, the user must have used png_malloc()
|
|---|
| 2894 | or png_zalloc() to allocate it.
|
|---|
| 2895 |
|
|---|
| 2896 | If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
|
|---|
| 2897 | separately, do not transfer responsibility for freeing text_ptr to libpng,
|
|---|
| 2898 | because when libpng fills a png_text structure it combines these members with
|
|---|
| 2899 | the key member, and png_free_data() will free only text_ptr.key. Similarly,
|
|---|
| 2900 | if you transfer responsibility for free'ing text_ptr from libpng to your
|
|---|
| 2901 | application, your application must not separately free those members.
|
|---|
| 2902 | For a more compact example of writing a PNG image, see the file example.c.
|
|---|
| 2903 |
|
|---|
| 2904 | .SH V. Modifying/Customizing libpng:
|
|---|
| 2905 |
|
|---|
| 2906 | There are two issues here. The first is changing how libpng does
|
|---|
| 2907 | standard things like memory allocation, input/output, and error handling.
|
|---|
| 2908 | The second deals with more complicated things like adding new chunks,
|
|---|
| 2909 | adding new transformations, and generally changing how libpng works.
|
|---|
| 2910 | Both of those are compile-time issues; that is, they are generally
|
|---|
| 2911 | determined at the time the code is written, and there is rarely a need
|
|---|
| 2912 | to provide the user with a means of changing them.
|
|---|
| 2913 |
|
|---|
| 2914 | Memory allocation, input/output, and error handling
|
|---|
| 2915 |
|
|---|
| 2916 | All of the memory allocation, input/output, and error handling in libpng
|
|---|
| 2917 | goes through callbacks that are user-settable. The default routines are
|
|---|
| 2918 | in pngmem.c, pngrio.c, pngwio.c, and pngerror.c, respectively. To change
|
|---|
| 2919 | these functions, call the appropriate png_set_*_fn() function.
|
|---|
| 2920 |
|
|---|
| 2921 | Memory allocation is done through the functions png_malloc(), png_calloc(),
|
|---|
| 2922 | and png_free(). These currently just call the standard C functions.
|
|---|
| 2923 | png_calloc() calls png_malloc() and then png_memset() to clear the newly
|
|---|
| 2924 | allocated memory to zero. If your pointers can't access more then 64K
|
|---|
| 2925 | at a time, you will want to set MAXSEG_64K in zlib.h. Since it is
|
|---|
| 2926 | unlikely that the method of handling memory allocation on a platform
|
|---|
| 2927 | will change between applications, these functions must be modified in
|
|---|
| 2928 | the library at compile time. If you prefer to use a different method
|
|---|
| 2929 | of allocating and freeing data, you can use png_create_read_struct_2() or
|
|---|
| 2930 | png_create_write_struct_2() to register your own functions as described
|
|---|
| 2931 | above. These functions also provide a void pointer that can be retrieved
|
|---|
| 2932 | via
|
|---|
| 2933 |
|
|---|
| 2934 | mem_ptr=png_get_mem_ptr(png_ptr);
|
|---|
| 2935 |
|
|---|
| 2936 | Your replacement memory functions must have prototypes as follows:
|
|---|
| 2937 |
|
|---|
| 2938 | png_voidp malloc_fn(png_structp png_ptr,
|
|---|
| 2939 | png_size_t size);
|
|---|
| 2940 | void free_fn(png_structp png_ptr, png_voidp ptr);
|
|---|
| 2941 |
|
|---|
| 2942 | Your malloc_fn() must return NULL in case of failure. The png_malloc()
|
|---|
| 2943 | function will normally call png_error() if it receives a NULL from the
|
|---|
| 2944 | system memory allocator or from your replacement malloc_fn().
|
|---|
| 2945 |
|
|---|
| 2946 | Your free_fn() will never be called with a NULL ptr, since libpng's
|
|---|
| 2947 | png_free() checks for NULL before calling free_fn().
|
|---|
| 2948 |
|
|---|
| 2949 | Input/Output in libpng is done through png_read() and png_write(),
|
|---|
| 2950 | which currently just call fread() and fwrite(). The FILE * is stored in
|
|---|
| 2951 | png_struct and is initialized via png_init_io(). If you wish to change
|
|---|
| 2952 | the method of I/O, the library supplies callbacks that you can set
|
|---|
| 2953 | through the function png_set_read_fn() and png_set_write_fn() at run
|
|---|
| 2954 | time, instead of calling the png_init_io() function. These functions
|
|---|
| 2955 | also provide a void pointer that can be retrieved via the function
|
|---|
| 2956 | png_get_io_ptr(). For example:
|
|---|
| 2957 |
|
|---|
| 2958 | png_set_read_fn(png_structp read_ptr,
|
|---|
| 2959 | voidp read_io_ptr, png_rw_ptr read_data_fn)
|
|---|
| 2960 |
|
|---|
| 2961 | png_set_write_fn(png_structp write_ptr,
|
|---|
| 2962 | voidp write_io_ptr, png_rw_ptr write_data_fn,
|
|---|
| 2963 | png_flush_ptr output_flush_fn);
|
|---|
| 2964 |
|
|---|
| 2965 | voidp read_io_ptr = png_get_io_ptr(read_ptr);
|
|---|
| 2966 | voidp write_io_ptr = png_get_io_ptr(write_ptr);
|
|---|
| 2967 |
|
|---|
| 2968 | The replacement I/O functions must have prototypes as follows:
|
|---|
| 2969 |
|
|---|
| 2970 | void user_read_data(png_structp png_ptr,
|
|---|
| 2971 | png_bytep data, png_size_t length);
|
|---|
| 2972 | void user_write_data(png_structp png_ptr,
|
|---|
| 2973 | png_bytep data, png_size_t length);
|
|---|
| 2974 | void user_flush_data(png_structp png_ptr);
|
|---|
| 2975 |
|
|---|
| 2976 | The user_read_data() function is responsible for detecting and
|
|---|
| 2977 | handling end-of-data errors.
|
|---|
| 2978 |
|
|---|
| 2979 | Supplying NULL for the read, write, or flush functions sets them back
|
|---|
| 2980 | to using the default C stream functions, which expect the io_ptr to
|
|---|
| 2981 | point to a standard *FILE structure. It is probably a mistake
|
|---|
| 2982 | to use NULL for one of write_data_fn and output_flush_fn but not both
|
|---|
| 2983 | of them, unless you have built libpng with PNG_NO_WRITE_FLUSH defined.
|
|---|
| 2984 | It is an error to read from a write stream, and vice versa.
|
|---|
| 2985 |
|
|---|
| 2986 | Error handling in libpng is done through png_error() and png_warning().
|
|---|
| 2987 | Errors handled through png_error() are fatal, meaning that png_error()
|
|---|
| 2988 | should never return to its caller. Currently, this is handled via
|
|---|
| 2989 | setjmp() and longjmp() (unless you have compiled libpng with
|
|---|
| 2990 | PNG_SETJMP_NOT_SUPPORTED, in which case it is handled via PNG_ABORT()),
|
|---|
| 2991 | but you could change this to do things like exit() if you should wish.
|
|---|
| 2992 |
|
|---|
| 2993 | On non-fatal errors, png_warning() is called
|
|---|
| 2994 | to print a warning message, and then control returns to the calling code.
|
|---|
| 2995 | By default png_error() and png_warning() print a message on stderr via
|
|---|
| 2996 | fprintf() unless the library is compiled with PNG_NO_CONSOLE_IO defined
|
|---|
| 2997 | (because you don't want the messages) or PNG_NO_STDIO defined (because
|
|---|
| 2998 | fprintf() isn't available). If you wish to change the behavior of the error
|
|---|
| 2999 | functions, you will need to set up your own message callbacks. These
|
|---|
| 3000 | functions are normally supplied at the time that the png_struct is created.
|
|---|
| 3001 | It is also possible to redirect errors and warnings to your own replacement
|
|---|
| 3002 | functions after png_create_*_struct() has been called by calling:
|
|---|
| 3003 |
|
|---|
| 3004 | png_set_error_fn(png_structp png_ptr,
|
|---|
| 3005 | png_voidp error_ptr, png_error_ptr error_fn,
|
|---|
| 3006 | png_error_ptr warning_fn);
|
|---|
| 3007 |
|
|---|
| 3008 | png_voidp error_ptr = png_get_error_ptr(png_ptr);
|
|---|
| 3009 |
|
|---|
| 3010 | If NULL is supplied for either error_fn or warning_fn, then the libpng
|
|---|
| 3011 | default function will be used, calling fprintf() and/or longjmp() if a
|
|---|
| 3012 | problem is encountered. The replacement error functions should have
|
|---|
| 3013 | parameters as follows:
|
|---|
| 3014 |
|
|---|
| 3015 | void user_error_fn(png_structp png_ptr,
|
|---|
| 3016 | png_const_charp error_msg);
|
|---|
| 3017 | void user_warning_fn(png_structp png_ptr,
|
|---|
| 3018 | png_const_charp warning_msg);
|
|---|
| 3019 |
|
|---|
| 3020 | The motivation behind using setjmp() and longjmp() is the C++ throw and
|
|---|
| 3021 | catch exception handling methods. This makes the code much easier to write,
|
|---|
| 3022 | as there is no need to check every return code of every function call.
|
|---|
| 3023 | However, there are some uncertainties about the status of local variables
|
|---|
| 3024 | after a longjmp, so the user may want to be careful about doing anything
|
|---|
| 3025 | after setjmp returns non-zero besides returning itself. Consult your
|
|---|
| 3026 | compiler documentation for more details. For an alternative approach, you
|
|---|
| 3027 | may wish to use the "cexcept" facility (see http://cexcept.sourceforge.net).
|
|---|
| 3028 |
|
|---|
| 3029 | .SS Custom chunks
|
|---|
| 3030 |
|
|---|
| 3031 | If you need to read or write custom chunks, you may need to get deeper
|
|---|
| 3032 | into the libpng code. The library now has mechanisms for storing
|
|---|
| 3033 | and writing chunks of unknown type; you can even declare callbacks
|
|---|
| 3034 | for custom chunks. However, this may not be good enough if the
|
|---|
| 3035 | library code itself needs to know about interactions between your
|
|---|
| 3036 | chunk and existing `intrinsic' chunks.
|
|---|
| 3037 |
|
|---|
| 3038 | If you need to write a new intrinsic chunk, first read the PNG
|
|---|
| 3039 | specification. Acquire a first level of understanding of how it works.
|
|---|
| 3040 | Pay particular attention to the sections that describe chunk names,
|
|---|
| 3041 | and look at how other chunks were designed, so you can do things
|
|---|
| 3042 | similarly. Second, check out the sections of libpng that read and
|
|---|
| 3043 | write chunks. Try to find a chunk that is similar to yours and use
|
|---|
| 3044 | it as a template. More details can be found in the comments inside
|
|---|
| 3045 | the code. It is best to handle unknown chunks in a generic method,
|
|---|
| 3046 | via callback functions, instead of by modifying libpng functions.
|
|---|
| 3047 |
|
|---|
| 3048 | If you wish to write your own transformation for the data, look through
|
|---|
| 3049 | the part of the code that does the transformations, and check out some of
|
|---|
| 3050 | the simpler ones to get an idea of how they work. Try to find a similar
|
|---|
| 3051 | transformation to the one you want to add and copy off of it. More details
|
|---|
| 3052 | can be found in the comments inside the code itself.
|
|---|
| 3053 |
|
|---|
| 3054 | .SS Configuring for 16 bit platforms
|
|---|
| 3055 |
|
|---|
| 3056 | You will want to look into zconf.h to tell zlib (and thus libpng) that
|
|---|
| 3057 | it cannot allocate more then 64K at a time. Even if you can, the memory
|
|---|
| 3058 | won't be accessible. So limit zlib and libpng to 64K by defining MAXSEG_64K.
|
|---|
| 3059 |
|
|---|
| 3060 | .SS Configuring for DOS
|
|---|
| 3061 |
|
|---|
| 3062 | For DOS users who only have access to the lower 640K, you will
|
|---|
| 3063 | have to limit zlib's memory usage via a png_set_compression_mem_level()
|
|---|
| 3064 | call. See zlib.h or zconf.h in the zlib library for more information.
|
|---|
| 3065 |
|
|---|
| 3066 | .SS Configuring for Medium Model
|
|---|
| 3067 |
|
|---|
| 3068 | Libpng's support for medium model has been tested on most of the popular
|
|---|
| 3069 | compilers. Make sure MAXSEG_64K gets defined, USE_FAR_KEYWORD gets
|
|---|
| 3070 | defined, and FAR gets defined to far in pngconf.h, and you should be
|
|---|
| 3071 | all set. Everything in the library (except for zlib's structure) is
|
|---|
| 3072 | expecting far data. You must use the typedefs with the p or pp on
|
|---|
| 3073 | the end for pointers (or at least look at them and be careful). Make
|
|---|
| 3074 | note that the rows of data are defined as png_bytepp, which is an
|
|---|
| 3075 | unsigned char far * far *.
|
|---|
| 3076 |
|
|---|
| 3077 | .SS Configuring for gui/windowing platforms:
|
|---|
| 3078 |
|
|---|
| 3079 | You will need to write new error and warning functions that use the GUI
|
|---|
| 3080 | interface, as described previously, and set them to be the error and
|
|---|
| 3081 | warning functions at the time that png_create_*_struct() is called,
|
|---|
| 3082 | in order to have them available during the structure initialization.
|
|---|
| 3083 | They can be changed later via png_set_error_fn(). On some compilers,
|
|---|
| 3084 | you may also have to change the memory allocators (png_malloc, etc.).
|
|---|
| 3085 |
|
|---|
| 3086 | .SS Configuring for compiler xxx:
|
|---|
| 3087 |
|
|---|
| 3088 | All includes for libpng are in pngconf.h. If you need to add, change
|
|---|
| 3089 | or delete an include, this is the place to do it.
|
|---|
| 3090 | The includes that are not needed outside libpng are protected by the
|
|---|
| 3091 | PNG_INTERNAL definition, which is only defined for those routines inside
|
|---|
| 3092 | libpng itself. The files in libpng proper only include png.h, which
|
|---|
| 3093 | includes pngconf.h.
|
|---|
| 3094 |
|
|---|
| 3095 | .SS Configuring zlib:
|
|---|
| 3096 |
|
|---|
| 3097 | There are special functions to configure the compression. Perhaps the
|
|---|
| 3098 | most useful one changes the compression level, which currently uses
|
|---|
| 3099 | input compression values in the range 0 - 9. The library normally
|
|---|
| 3100 | uses the default compression level (Z_DEFAULT_COMPRESSION = 6). Tests
|
|---|
| 3101 | have shown that for a large majority of images, compression values in
|
|---|
| 3102 | the range 3-6 compress nearly as well as higher levels, and do so much
|
|---|
| 3103 | faster. For online applications it may be desirable to have maximum speed
|
|---|
| 3104 | (Z_BEST_SPEED = 1). With versions of zlib after v0.99, you can also
|
|---|
| 3105 | specify no compression (Z_NO_COMPRESSION = 0), but this would create
|
|---|
| 3106 | files larger than just storing the raw bitmap. You can specify the
|
|---|
| 3107 | compression level by calling:
|
|---|
| 3108 |
|
|---|
| 3109 | png_set_compression_level(png_ptr, level);
|
|---|
| 3110 |
|
|---|
| 3111 | Another useful one is to reduce the memory level used by the library.
|
|---|
| 3112 | The memory level defaults to 8, but it can be lowered if you are
|
|---|
| 3113 | short on memory (running DOS, for example, where you only have 640K).
|
|---|
| 3114 | Note that the memory level does have an effect on compression; among
|
|---|
| 3115 | other things, lower levels will result in sections of incompressible
|
|---|
| 3116 | data being emitted in smaller stored blocks, with a correspondingly
|
|---|
| 3117 | larger relative overhead of up to 15% in the worst case.
|
|---|
| 3118 |
|
|---|
| 3119 | png_set_compression_mem_level(png_ptr, level);
|
|---|
| 3120 |
|
|---|
| 3121 | The other functions are for configuring zlib. They are not recommended
|
|---|
| 3122 | for normal use and may result in writing an invalid PNG file. See
|
|---|
| 3123 | zlib.h for more information on what these mean.
|
|---|
| 3124 |
|
|---|
| 3125 | png_set_compression_strategy(png_ptr,
|
|---|
| 3126 | strategy);
|
|---|
| 3127 | png_set_compression_window_bits(png_ptr,
|
|---|
| 3128 | window_bits);
|
|---|
| 3129 | png_set_compression_method(png_ptr, method);
|
|---|
| 3130 | png_set_compression_buffer_size(png_ptr, size);
|
|---|
| 3131 |
|
|---|
| 3132 | .SS Controlling row filtering
|
|---|
| 3133 |
|
|---|
| 3134 | If you want to control whether libpng uses filtering or not, which
|
|---|
| 3135 | filters are used, and how it goes about picking row filters, you
|
|---|
| 3136 | can call one of these functions. The selection and configuration
|
|---|
| 3137 | of row filters can have a significant impact on the size and
|
|---|
| 3138 | encoding speed and a somewhat lesser impact on the decoding speed
|
|---|
| 3139 | of an image. Filtering is enabled by default for RGB and grayscale
|
|---|
| 3140 | images (with and without alpha), but not for paletted images nor
|
|---|
| 3141 | for any images with bit depths less than 8 bits/pixel.
|
|---|
| 3142 |
|
|---|
| 3143 | The 'method' parameter sets the main filtering method, which is
|
|---|
| 3144 | currently only '0' in the PNG 1.2 specification. The 'filters'
|
|---|
| 3145 | parameter sets which filter(s), if any, should be used for each
|
|---|
| 3146 | scanline. Possible values are PNG_ALL_FILTERS and PNG_NO_FILTERS
|
|---|
| 3147 | to turn filtering on and off, respectively.
|
|---|
| 3148 |
|
|---|
| 3149 | Individual filter types are PNG_FILTER_NONE, PNG_FILTER_SUB,
|
|---|
| 3150 | PNG_FILTER_UP, PNG_FILTER_AVG, PNG_FILTER_PAETH, which can be bitwise
|
|---|
| 3151 | ORed together with '|' to specify one or more filters to use.
|
|---|
| 3152 | These filters are described in more detail in the PNG specification.
|
|---|
| 3153 | If you intend to change the filter type during the course of writing
|
|---|
| 3154 | the image, you should start with flags set for all of the filters
|
|---|
| 3155 | you intend to use so that libpng can initialize its internal
|
|---|
| 3156 | structures appropriately for all of the filter types. (Note that this
|
|---|
| 3157 | means the first row must always be adaptively filtered, because libpng
|
|---|
| 3158 | currently does not allocate the filter buffers until png_write_row()
|
|---|
| 3159 | is called for the first time.)
|
|---|
| 3160 |
|
|---|
| 3161 | filters = PNG_FILTER_NONE | PNG_FILTER_SUB
|
|---|
| 3162 | PNG_FILTER_UP | PNG_FILTER_AVG |
|
|---|
| 3163 | PNG_FILTER_PAETH | PNG_ALL_FILTERS;
|
|---|
| 3164 |
|
|---|
| 3165 | png_set_filter(png_ptr, PNG_FILTER_TYPE_BASE,
|
|---|
| 3166 | filters);
|
|---|
| 3167 | The second parameter can also be
|
|---|
| 3168 | PNG_INTRAPIXEL_DIFFERENCING if you are
|
|---|
| 3169 | writing a PNG to be embedded in a MNG
|
|---|
| 3170 | datastream. This parameter must be the
|
|---|
| 3171 | same as the value of filter_method used
|
|---|
| 3172 | in png_set_IHDR().
|
|---|
| 3173 |
|
|---|
| 3174 | .SS Removing unwanted object code
|
|---|
| 3175 |
|
|---|
| 3176 | There are a bunch of #define's in pngconf.h that control what parts of
|
|---|
| 3177 | libpng are compiled. All the defines end in _SUPPORTED. If you are
|
|---|
| 3178 | never going to use a capability, you can change the #define to #undef
|
|---|
| 3179 | before recompiling libpng and save yourself code and data space, or
|
|---|
| 3180 | you can turn off individual capabilities with defines that begin with
|
|---|
| 3181 | PNG_NO_.
|
|---|
| 3182 |
|
|---|
| 3183 | You can also turn all of the transforms and ancillary chunk capabilities
|
|---|
| 3184 | off en masse with compiler directives that define
|
|---|
| 3185 | PNG_NO_READ[or WRITE]_TRANSFORMS, or PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS,
|
|---|
| 3186 | or all four,
|
|---|
| 3187 | along with directives to turn on any of the capabilities that you do
|
|---|
| 3188 | want. The PNG_NO_READ[or WRITE]_TRANSFORMS directives disable the extra
|
|---|
| 3189 | transformations but still leave the library fully capable of reading
|
|---|
| 3190 | and writing PNG files with all known public chunks. Use of the
|
|---|
| 3191 | PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS directive produces a library
|
|---|
| 3192 | that is incapable of reading or writing ancillary chunks. If you are
|
|---|
| 3193 | not using the progressive reading capability, you can turn that off
|
|---|
| 3194 | with PNG_NO_PROGRESSIVE_READ (don't confuse this with the INTERLACING
|
|---|
| 3195 | capability, which you'll still have).
|
|---|
| 3196 |
|
|---|
| 3197 | All the reading and writing specific code are in separate files, so the
|
|---|
| 3198 | linker should only grab the files it needs. However, if you want to
|
|---|
| 3199 | make sure, or if you are building a stand alone library, all the
|
|---|
| 3200 | reading files start with pngr and all the writing files start with
|
|---|
| 3201 | pngw. The files that don't match either (like png.c, pngtrans.c, etc.)
|
|---|
| 3202 | are used for both reading and writing, and always need to be included.
|
|---|
| 3203 | The progressive reader is in pngpread.c
|
|---|
| 3204 |
|
|---|
| 3205 | If you are creating or distributing a dynamically linked library (a .so
|
|---|
| 3206 | or DLL file), you should not remove or disable any parts of the library,
|
|---|
| 3207 | as this will cause applications linked with different versions of the
|
|---|
| 3208 | library to fail if they call functions not available in your library.
|
|---|
| 3209 | The size of the library itself should not be an issue, because only
|
|---|
| 3210 | those sections that are actually used will be loaded into memory.
|
|---|
| 3211 |
|
|---|
| 3212 | .SS Requesting debug printout
|
|---|
| 3213 |
|
|---|
| 3214 | The macro definition PNG_DEBUG can be used to request debugging
|
|---|
| 3215 | printout. Set it to an integer value in the range 0 to 3. Higher
|
|---|
| 3216 | numbers result in increasing amounts of debugging information. The
|
|---|
| 3217 | information is printed to the "stderr" file, unless another file
|
|---|
| 3218 | name is specified in the PNG_DEBUG_FILE macro definition.
|
|---|
| 3219 |
|
|---|
| 3220 | When PNG_DEBUG > 0, the following functions (macros) become available:
|
|---|
| 3221 |
|
|---|
| 3222 | png_debug(level, message)
|
|---|
| 3223 | png_debug1(level, message, p1)
|
|---|
| 3224 | png_debug2(level, message, p1, p2)
|
|---|
| 3225 |
|
|---|
| 3226 | in which "level" is compared to PNG_DEBUG to decide whether to print
|
|---|
| 3227 | the message, "message" is the formatted string to be printed,
|
|---|
| 3228 | and p1 and p2 are parameters that are to be embedded in the string
|
|---|
| 3229 | according to printf-style formatting directives. For example,
|
|---|
| 3230 |
|
|---|
| 3231 | png_debug1(2, "foo=%d", foo);
|
|---|
| 3232 |
|
|---|
| 3233 | is expanded to
|
|---|
| 3234 |
|
|---|
| 3235 | if(PNG_DEBUG > 2)
|
|---|
| 3236 | fprintf(PNG_DEBUG_FILE, "foo=%d\en", foo);
|
|---|
| 3237 |
|
|---|
| 3238 | When PNG_DEBUG is defined but is zero, the macros aren't defined, but you
|
|---|
| 3239 | can still use PNG_DEBUG to control your own debugging:
|
|---|
| 3240 |
|
|---|
| 3241 | #ifdef PNG_DEBUG
|
|---|
| 3242 | fprintf(stderr, ...
|
|---|
| 3243 | #endif
|
|---|
| 3244 |
|
|---|
| 3245 | When PNG_DEBUG = 1, the macros are defined, but only png_debug statements
|
|---|
| 3246 | having level = 0 will be printed. There aren't any such statements in
|
|---|
| 3247 | this version of libpng, but if you insert some they will be printed.
|
|---|
| 3248 |
|
|---|
| 3249 | .SH VI. MNG support
|
|---|
| 3250 |
|
|---|
| 3251 | The MNG specification (available at http://www.libpng.org/pub/mng) allows
|
|---|
| 3252 | certain extensions to PNG for PNG images that are embedded in MNG datastreams.
|
|---|
| 3253 | Libpng can support some of these extensions. To enable them, use the
|
|---|
| 3254 | png_permit_mng_features() function:
|
|---|
| 3255 |
|
|---|
| 3256 | feature_set = png_permit_mng_features(png_ptr, mask)
|
|---|
| 3257 | mask is a png_uint_32 containing the bitwise OR of the
|
|---|
| 3258 | features you want to enable. These include
|
|---|
| 3259 | PNG_FLAG_MNG_EMPTY_PLTE
|
|---|
| 3260 | PNG_FLAG_MNG_FILTER_64
|
|---|
| 3261 | PNG_ALL_MNG_FEATURES
|
|---|
| 3262 | feature_set is a png_uint_32 that is the bitwise AND of
|
|---|
| 3263 | your mask with the set of MNG features that is
|
|---|
| 3264 | supported by the version of libpng that you are using.
|
|---|
| 3265 |
|
|---|
| 3266 | It is an error to use this function when reading or writing a standalone
|
|---|
| 3267 | PNG file with the PNG 8-byte signature. The PNG datastream must be wrapped
|
|---|
| 3268 | in a MNG datastream. As a minimum, it must have the MNG 8-byte signature
|
|---|
| 3269 | and the MHDR and MEND chunks. Libpng does not provide support for these
|
|---|
| 3270 | or any other MNG chunks; your application must provide its own support for
|
|---|
| 3271 | them. You may wish to consider using libmng (available at
|
|---|
| 3272 | http://www.libmng.com) instead.
|
|---|
| 3273 |
|
|---|
| 3274 | .SH VII. Changes to Libpng from version 0.88
|
|---|
| 3275 |
|
|---|
| 3276 | It should be noted that versions of libpng later than 0.96 are not
|
|---|
| 3277 | distributed by the original libpng author, Guy Schalnat, nor by
|
|---|
| 3278 | Andreas Dilger, who had taken over from Guy during 1996 and 1997, and
|
|---|
| 3279 | distributed versions 0.89 through 0.96, but rather by another member
|
|---|
| 3280 | of the original PNG Group, Glenn Randers-Pehrson. Guy and Andreas are
|
|---|
| 3281 | still alive and well, but they have moved on to other things.
|
|---|
| 3282 |
|
|---|
| 3283 | The old libpng functions png_read_init(), png_write_init(),
|
|---|
| 3284 | png_info_init(), png_read_destroy(), and png_write_destroy() have been
|
|---|
| 3285 | moved to PNG_INTERNAL in version 0.95 to discourage their use. These
|
|---|
| 3286 | functions will be removed from libpng version 2.0.0.
|
|---|
| 3287 |
|
|---|
| 3288 | The preferred method of creating and initializing the libpng structures is
|
|---|
| 3289 | via the png_create_read_struct(), png_create_write_struct(), and
|
|---|
| 3290 | png_create_info_struct() because they isolate the size of the structures
|
|---|
| 3291 | from the application, allow version error checking, and also allow the
|
|---|
| 3292 | use of custom error handling routines during the initialization, which
|
|---|
| 3293 | the old functions do not. The functions png_read_destroy() and
|
|---|
| 3294 | png_write_destroy() do not actually free the memory that libpng
|
|---|
| 3295 | allocated for these structs, but just reset the data structures, so they
|
|---|
| 3296 | can be used instead of png_destroy_read_struct() and
|
|---|
| 3297 | png_destroy_write_struct() if you feel there is too much system overhead
|
|---|
| 3298 | allocating and freeing the png_struct for each image read.
|
|---|
| 3299 |
|
|---|
| 3300 | Setting the error callbacks via png_set_message_fn() before
|
|---|
| 3301 | png_read_init() as was suggested in libpng-0.88 is no longer supported
|
|---|
| 3302 | because this caused applications that do not use custom error functions
|
|---|
| 3303 | to fail if the png_ptr was not initialized to zero. It is still possible
|
|---|
| 3304 | to set the error callbacks AFTER png_read_init(), or to change them with
|
|---|
| 3305 | png_set_error_fn(), which is essentially the same function, but with a new
|
|---|
| 3306 | name to force compilation errors with applications that try to use the old
|
|---|
| 3307 | method.
|
|---|
| 3308 |
|
|---|
| 3309 | Support for the sCAL, iCCP, iTXt, and sPLT chunks was added at libpng-1.0.6;
|
|---|
| 3310 | however, iTXt support was not enabled by default.
|
|---|
| 3311 |
|
|---|
| 3312 | Starting with version 1.0.7, you can find out which version of the library
|
|---|
| 3313 | you are using at run-time:
|
|---|
| 3314 |
|
|---|
| 3315 | png_uint_32 libpng_vn = png_access_version_number();
|
|---|
| 3316 |
|
|---|
| 3317 | The number libpng_vn is constructed from the major version, minor
|
|---|
| 3318 | version with leading zero, and release number with leading zero,
|
|---|
| 3319 | (e.g., libpng_vn for version 1.0.7 is 10007).
|
|---|
| 3320 |
|
|---|
| 3321 | You can also check which version of png.h you used when compiling your
|
|---|
| 3322 | application:
|
|---|
| 3323 |
|
|---|
| 3324 | png_uint_32 application_vn = PNG_LIBPNG_VER;
|
|---|
| 3325 |
|
|---|
| 3326 | .SH VIII. Changes to Libpng from version 1.0.x to 1.2.x
|
|---|
| 3327 |
|
|---|
| 3328 | Support for user memory management was enabled by default. To
|
|---|
| 3329 | accomplish this, the functions png_create_read_struct_2(),
|
|---|
| 3330 | png_create_write_struct_2(), png_set_mem_fn(), png_get_mem_ptr(),
|
|---|
| 3331 | png_malloc_default(), and png_free_default() were added.
|
|---|
| 3332 |
|
|---|
| 3333 | Support for the iTXt chunk has been enabled by default as of
|
|---|
| 3334 | version 1.2.41.
|
|---|
| 3335 |
|
|---|
| 3336 | Support for certain MNG features was enabled.
|
|---|
| 3337 |
|
|---|
| 3338 | Support for numbered error messages was added. However, we never got
|
|---|
| 3339 | around to actually numbering the error messages. The function
|
|---|
| 3340 | png_set_strip_error_numbers() was added (Note: the prototype for this
|
|---|
| 3341 | function was inadvertently removed from png.h in PNG_NO_ASSEMBLER_CODE
|
|---|
| 3342 | builds of libpng-1.2.15. It was restored in libpng-1.2.36).
|
|---|
| 3343 |
|
|---|
| 3344 | The png_malloc_warn() function was added at libpng-1.2.3. This issues
|
|---|
| 3345 | a png_warning and returns NULL instead of aborting when it fails to
|
|---|
| 3346 | acquire the requested memory allocation.
|
|---|
| 3347 |
|
|---|
| 3348 | Support for setting user limits on image width and height was enabled
|
|---|
| 3349 | by default. The functions png_set_user_limits(), png_get_user_width_max(),
|
|---|
| 3350 | and png_get_user_height_max() were added at libpng-1.2.6.
|
|---|
| 3351 |
|
|---|
| 3352 | The png_set_add_alpha() function was added at libpng-1.2.7.
|
|---|
| 3353 |
|
|---|
| 3354 | The function png_set_expand_gray_1_2_4_to_8() was added at libpng-1.2.9.
|
|---|
| 3355 | Unlike png_set_gray_1_2_4_to_8(), the new function does not expand the
|
|---|
| 3356 | tRNS chunk to alpha. The png_set_gray_1_2_4_to_8() function is
|
|---|
| 3357 | deprecated.
|
|---|
| 3358 |
|
|---|
| 3359 | A number of macro definitions in support of runtime selection of
|
|---|
| 3360 | assembler code features (especially Intel MMX code support) were
|
|---|
| 3361 | added at libpng-1.2.0:
|
|---|
| 3362 |
|
|---|
| 3363 | PNG_ASM_FLAG_MMX_SUPPORT_COMPILED
|
|---|
| 3364 | PNG_ASM_FLAG_MMX_SUPPORT_IN_CPU
|
|---|
| 3365 | PNG_ASM_FLAG_MMX_READ_COMBINE_ROW
|
|---|
| 3366 | PNG_ASM_FLAG_MMX_READ_INTERLACE
|
|---|
| 3367 | PNG_ASM_FLAG_MMX_READ_FILTER_SUB
|
|---|
| 3368 | PNG_ASM_FLAG_MMX_READ_FILTER_UP
|
|---|
| 3369 | PNG_ASM_FLAG_MMX_READ_FILTER_AVG
|
|---|
| 3370 | PNG_ASM_FLAG_MMX_READ_FILTER_PAETH
|
|---|
| 3371 | PNG_ASM_FLAGS_INITIALIZED
|
|---|
| 3372 | PNG_MMX_READ_FLAGS
|
|---|
| 3373 | PNG_MMX_FLAGS
|
|---|
| 3374 | PNG_MMX_WRITE_FLAGS
|
|---|
| 3375 | PNG_MMX_FLAGS
|
|---|
| 3376 |
|
|---|
| 3377 | We added the following functions in support of runtime
|
|---|
| 3378 | selection of assembler code features:
|
|---|
| 3379 |
|
|---|
| 3380 | png_get_mmx_flagmask()
|
|---|
| 3381 | png_set_mmx_thresholds()
|
|---|
| 3382 | png_get_asm_flags()
|
|---|
| 3383 | png_get_mmx_bitdepth_threshold()
|
|---|
| 3384 | png_get_mmx_rowbytes_threshold()
|
|---|
| 3385 | png_set_asm_flags()
|
|---|
| 3386 |
|
|---|
| 3387 | We replaced all of these functions with simple stubs in libpng-1.2.20,
|
|---|
| 3388 | when the Intel assembler code was removed due to a licensing issue.
|
|---|
| 3389 |
|
|---|
| 3390 | These macros are deprecated:
|
|---|
| 3391 |
|
|---|
| 3392 | PNG_READ_TRANSFORMS_NOT_SUPPORTED
|
|---|
| 3393 | PNG_PROGRESSIVE_READ_NOT_SUPPORTED
|
|---|
| 3394 | PNG_NO_SEQUENTIAL_READ_SUPPORTED
|
|---|
| 3395 | PNG_WRITE_TRANSFORMS_NOT_SUPPORTED
|
|---|
| 3396 | PNG_READ_ANCILLARY_CHUNKS_NOT_SUPPORTED
|
|---|
| 3397 | PNG_WRITE_ANCILLARY_CHUNKS_NOT_SUPPORTED
|
|---|
| 3398 |
|
|---|
| 3399 | They have been replaced, respectively, by:
|
|---|
| 3400 |
|
|---|
| 3401 | PNG_NO_READ_TRANSFORMS
|
|---|
| 3402 | PNG_NO_PROGRESSIVE_READ
|
|---|
| 3403 | PNG_NO_SEQUENTIAL_READ
|
|---|
| 3404 | PNG_NO_WRITE_TRANSFORMS
|
|---|
| 3405 | PNG_NO_READ_ANCILLARY_CHUNKS
|
|---|
| 3406 | PNG_NO_WRITE_ANCILLARY_CHUNKS
|
|---|
| 3407 |
|
|---|
| 3408 | PNG_MAX_UINT was replaced with PNG_UINT_31_MAX. It has been
|
|---|
| 3409 | deprecated since libpng-1.0.16 and libpng-1.2.6.
|
|---|
| 3410 |
|
|---|
| 3411 | The function
|
|---|
| 3412 | png_check_sig(sig, num)
|
|---|
| 3413 | was replaced with
|
|---|
| 3414 | !png_sig_cmp(sig, 0, num)
|
|---|
| 3415 | It has been deprecated since libpng-0.90.
|
|---|
| 3416 |
|
|---|
| 3417 | The function
|
|---|
| 3418 | png_set_gray_1_2_4_to_8()
|
|---|
| 3419 | which also expands tRNS to alpha was replaced with
|
|---|
| 3420 | png_set_expand_gray_1_2_4_to_8()
|
|---|
| 3421 | which does not. It has been deprecated since libpng-1.0.18 and 1.2.9.
|
|---|
| 3422 |
|
|---|
| 3423 | .SH IX. (Omitted)
|
|---|
| 3424 |
|
|---|
| 3425 |
|
|---|
| 3426 | Starting with libpng-1.2.54, attempting to set an over-length
|
|---|
| 3427 | PLTE chunk is an error. Previously this requirement of the PNG specification
|
|---|
| 3428 | was not enforced, and the palette was always limited to 256 entries.
|
|---|
| 3429 | An over-length PLTE chunk found in an input PNG is silently truncated.
|
|---|
| 3430 |
|
|---|
| 3431 | .SH X. Detecting libpng
|
|---|
| 3432 |
|
|---|
| 3433 | The png_get_io_ptr() function has been present since libpng-0.88, has never
|
|---|
| 3434 | changed, and is unaffected by conditional compilation macros. It is the
|
|---|
| 3435 | best choice for use in configure scripts for detecting the presence of any
|
|---|
| 3436 | libpng version since 0.88. In an autoconf "configure.in" you could use
|
|---|
| 3437 |
|
|---|
| 3438 | AC_CHECK_LIB(png, png_get_io_ptr, ...
|
|---|
| 3439 |
|
|---|
| 3440 | .SH XI. Source code repository
|
|---|
| 3441 |
|
|---|
| 3442 | Since about February 2009, version 1.2.34, libpng has been under "git" source
|
|---|
| 3443 | control. The git repository was built from old libpng-x.y.z.tar.gz files
|
|---|
| 3444 | going back to version 0.70. You can access the git repository (read only)
|
|---|
| 3445 | at
|
|---|
| 3446 |
|
|---|
| 3447 | git://git.code.sf.net/p/libpng/code
|
|---|
| 3448 |
|
|---|
| 3449 | or you can browse it with a web browser by selecting the "code" button at
|
|---|
| 3450 |
|
|---|
| 3451 | https://sourceforge.net/projects/libpng/
|
|---|
| 3452 |
|
|---|
| 3453 | Patches can be sent to glennrp at users.sourceforge.net or to
|
|---|
| 3454 | png-mng-implement at lists.sourceforge.net or you can upload them to
|
|---|
| 3455 | the libpng bug tracker at
|
|---|
| 3456 |
|
|---|
| 3457 | http://libpng.sourceforge.net
|
|---|
| 3458 |
|
|---|
| 3459 | .SH XII. Coding style
|
|---|
| 3460 |
|
|---|
| 3461 | Our coding style is similar to the "Allman" style
|
|---|
| 3462 | (See http://en.wikipedia.org/wiki/Indent_style#Allman_style), with curly
|
|---|
| 3463 | braces on separate lines:
|
|---|
| 3464 |
|
|---|
| 3465 | if (condition)
|
|---|
| 3466 | {
|
|---|
| 3467 | action;
|
|---|
| 3468 | }
|
|---|
| 3469 |
|
|---|
| 3470 | else if (another condition)
|
|---|
| 3471 | {
|
|---|
| 3472 | another action;
|
|---|
| 3473 | }
|
|---|
| 3474 |
|
|---|
| 3475 | The braces can be omitted from simple one-line actions:
|
|---|
| 3476 |
|
|---|
| 3477 | if (condition)
|
|---|
| 3478 | return (0);
|
|---|
| 3479 |
|
|---|
| 3480 | We use 3-space indentation, except for continued statements which
|
|---|
| 3481 | are usually indented the same as the first line of the statement
|
|---|
| 3482 | plus four more spaces.
|
|---|
| 3483 |
|
|---|
| 3484 | For macro definitions we use 2-space indentation, always leaving the "#"
|
|---|
| 3485 | in the first column.
|
|---|
| 3486 |
|
|---|
| 3487 | #ifndef PNG_NO_FEATURE
|
|---|
| 3488 | # ifndef PNG_FEATURE_SUPPORTED
|
|---|
| 3489 | # define PNG_FEATURE_SUPPORTED
|
|---|
| 3490 | # endif
|
|---|
| 3491 | #endif
|
|---|
| 3492 |
|
|---|
| 3493 | Comments appear with the leading "/*" at the same indentation as
|
|---|
| 3494 | the statement that follows the comment:
|
|---|
| 3495 |
|
|---|
| 3496 | /* Single-line comment */
|
|---|
| 3497 | statement;
|
|---|
| 3498 |
|
|---|
| 3499 | /* Multiple-line
|
|---|
| 3500 | * comment
|
|---|
| 3501 | */
|
|---|
| 3502 | statement;
|
|---|
| 3503 |
|
|---|
| 3504 | Very short comments can be placed at the end of the statement
|
|---|
| 3505 | to which they pertain:
|
|---|
| 3506 |
|
|---|
| 3507 | statement; /* comment */
|
|---|
| 3508 |
|
|---|
| 3509 | We don't use C++ style ("//") comments. We have, however,
|
|---|
| 3510 | used them in the past in some now-abandoned MMX assembler
|
|---|
| 3511 | code.
|
|---|
| 3512 |
|
|---|
| 3513 | Functions and their curly braces are not indented, and
|
|---|
| 3514 | exported functions are marked with PNGAPI:
|
|---|
| 3515 |
|
|---|
| 3516 | /* This is a public function that is visible to
|
|---|
| 3517 | * application programers. It does thus-and-so.
|
|---|
| 3518 | */
|
|---|
| 3519 | void PNGAPI
|
|---|
| 3520 | png_exported_function(png_ptr, png_info, foo)
|
|---|
| 3521 | {
|
|---|
| 3522 | body;
|
|---|
| 3523 | }
|
|---|
| 3524 |
|
|---|
| 3525 | The prototypes for all exported functions appear in png.h,
|
|---|
| 3526 | above the comment that says
|
|---|
| 3527 |
|
|---|
| 3528 | /* Maintainer: Put new public prototypes here ... */
|
|---|
| 3529 |
|
|---|
| 3530 | We mark all non-exported functions with "/* PRIVATE */"":
|
|---|
| 3531 |
|
|---|
| 3532 | void /* PRIVATE */
|
|---|
| 3533 | png_non_exported_function(png_ptr, png_info, foo)
|
|---|
| 3534 | {
|
|---|
| 3535 | body;
|
|---|
| 3536 | }
|
|---|
| 3537 |
|
|---|
| 3538 | The prototypes for non-exported functions (except for those in
|
|---|
| 3539 | pngtest) appear in
|
|---|
| 3540 | the PNG_INTERNAL section of png.h
|
|---|
| 3541 | above the comment that says
|
|---|
| 3542 |
|
|---|
| 3543 | /* Maintainer: Put new private prototypes here ^ and in libpngpf.3 */
|
|---|
| 3544 |
|
|---|
| 3545 | The names of all exported functions and variables begin
|
|---|
| 3546 | with "png_", and all publicly visible C preprocessor
|
|---|
| 3547 | macros begin with "PNG".
|
|---|
| 3548 |
|
|---|
| 3549 | We put a space after each comma and after each semicolon
|
|---|
| 3550 | in "for" statments, and we put spaces before and after each
|
|---|
| 3551 | C binary operator and after "for" or "while". We don't
|
|---|
| 3552 | put a space between a typecast and the expression being
|
|---|
| 3553 | cast, nor do we put one between a function name and the
|
|---|
| 3554 | left parenthesis that follows it:
|
|---|
| 3555 |
|
|---|
| 3556 | for (i = 2; i > 0; --i)
|
|---|
| 3557 | y[i] = a(x) + (int)b;
|
|---|
| 3558 |
|
|---|
| 3559 | We prefer #ifdef and #ifndef to #if defined() and if !defined()
|
|---|
| 3560 | when there is only one macro being tested.
|
|---|
| 3561 |
|
|---|
| 3562 | We do not use the TAB character for indentation in the C sources.
|
|---|
| 3563 |
|
|---|
| 3564 | Lines do not exceed 80 characters.
|
|---|
| 3565 |
|
|---|
| 3566 | Other rules can be inferred by inspecting the libpng source.
|
|---|
| 3567 |
|
|---|
| 3568 | .SH XIII. Y2K Compliance in libpng
|
|---|
| 3569 |
|
|---|
| 3570 | Since the PNG Development group is an ad-hoc body, we can't make
|
|---|
| 3571 | an official declaration.
|
|---|
| 3572 |
|
|---|
| 3573 | This is your unofficial assurance that libpng from version 0.71 and
|
|---|
| 3574 | upward through 1.2.54 are Y2K compliant. It is my belief that earlier
|
|---|
| 3575 | versions were also Y2K compliant.
|
|---|
| 3576 |
|
|---|
| 3577 | Libpng only has three year fields. One is a 2-byte unsigned integer that
|
|---|
| 3578 | will hold years up to 65535. The other two hold the date in text
|
|---|
| 3579 | format, and will hold years up to 9999.
|
|---|
| 3580 |
|
|---|
| 3581 | The integer is
|
|---|
| 3582 | "png_uint_16 year" in png_time_struct.
|
|---|
| 3583 |
|
|---|
| 3584 | The strings are
|
|---|
| 3585 | "png_charp time_buffer" in png_struct and
|
|---|
| 3586 | "near_time_buffer", which is a local character string in png.c.
|
|---|
| 3587 |
|
|---|
| 3588 | There are seven time-related functions:
|
|---|
| 3589 |
|
|---|
| 3590 | png_convert_to_rfc_1123() in png.c
|
|---|
| 3591 | (formerly png_convert_to_rfc_1152() in error)
|
|---|
| 3592 | png_convert_from_struct_tm() in pngwrite.c, called
|
|---|
| 3593 | in pngwrite.c
|
|---|
| 3594 | png_convert_from_time_t() in pngwrite.c
|
|---|
| 3595 | png_get_tIME() in pngget.c
|
|---|
| 3596 | png_handle_tIME() in pngrutil.c, called in pngread.c
|
|---|
| 3597 | png_set_tIME() in pngset.c
|
|---|
| 3598 | png_write_tIME() in pngwutil.c, called in pngwrite.c
|
|---|
| 3599 |
|
|---|
| 3600 | All appear to handle dates properly in a Y2K environment. The
|
|---|
| 3601 | png_convert_from_time_t() function calls gmtime() to convert from system
|
|---|
| 3602 | clock time, which returns (year - 1900), which we properly convert to
|
|---|
| 3603 | the full 4-digit year. There is a possibility that applications using
|
|---|
| 3604 | libpng are not passing 4-digit years into the png_convert_to_rfc_1123()
|
|---|
| 3605 | function, or that they are incorrectly passing only a 2-digit year
|
|---|
| 3606 | instead of "year - 1900" into the png_convert_from_struct_tm() function,
|
|---|
| 3607 | but this is not under our control. The libpng documentation has always
|
|---|
| 3608 | stated that it works with 4-digit years, and the APIs have been
|
|---|
| 3609 | documented as such.
|
|---|
| 3610 |
|
|---|
| 3611 | The tIME chunk itself is also Y2K compliant. It uses a 2-byte unsigned
|
|---|
| 3612 | integer to hold the year, and can hold years as large as 65535.
|
|---|
| 3613 |
|
|---|
| 3614 | zlib, upon which libpng depends, is also Y2K compliant. It contains
|
|---|
| 3615 | no date-related code.
|
|---|
| 3616 |
|
|---|
| 3617 |
|
|---|
| 3618 | Glenn Randers-Pehrson
|
|---|
| 3619 | libpng maintainer
|
|---|
| 3620 | PNG Development Group
|
|---|
| 3621 |
|
|---|
| 3622 | .SH NOTE
|
|---|
| 3623 |
|
|---|
| 3624 | Note about libpng version numbers:
|
|---|
| 3625 |
|
|---|
| 3626 | Due to various miscommunications, unforeseen code incompatibilities
|
|---|
| 3627 | and occasional factors outside the authors' control, version numbering
|
|---|
| 3628 | on the library has not always been consistent and straightforward.
|
|---|
| 3629 | The following table summarizes matters since version 0.89c, which was
|
|---|
| 3630 | the first widely used release:
|
|---|
| 3631 |
|
|---|
| 3632 | source png.h png.h shared-lib
|
|---|
| 3633 | version string int version
|
|---|
| 3634 | ------- ------ ----- ----------
|
|---|
| 3635 | 0.89c "1.0 beta 3" 0.89 89 1.0.89
|
|---|
| 3636 | 0.90 "1.0 beta 4" 0.90 90 0.90 [should have been 2.0.90]
|
|---|
| 3637 | 0.95 "1.0 beta 5" 0.95 95 0.95 [should have been 2.0.95]
|
|---|
| 3638 | 0.96 "1.0 beta 6" 0.96 96 0.96 [should have been 2.0.96]
|
|---|
| 3639 | 0.97b "1.00.97 beta 7" 1.00.97 97 1.0.1 [should have been 2.0.97]
|
|---|
| 3640 | 0.97c 0.97 97 2.0.97
|
|---|
| 3641 | 0.98 0.98 98 2.0.98
|
|---|
| 3642 | 0.99 0.99 98 2.0.99
|
|---|
| 3643 | 0.99a-m 0.99 99 2.0.99
|
|---|
| 3644 | 1.00 1.00 100 2.1.0 [100 should be 10000]
|
|---|
| 3645 | 1.0.0 (from here on, the 100 2.1.0 [100 should be 10000]
|
|---|
| 3646 | 1.0.1 png.h string is 10001 2.1.0
|
|---|
| 3647 | 1.0.1a-e identical to the 10002 from here on, the shared library
|
|---|
| 3648 | 1.0.2 source version) 10002 is 2.V where V is the source code
|
|---|
| 3649 | 1.0.2a-b 10003 version, except as noted.
|
|---|
| 3650 | 1.0.3 10003
|
|---|
| 3651 | 1.0.3a-d 10004
|
|---|
| 3652 | 1.0.4 10004
|
|---|
| 3653 | 1.0.4a-f 10005
|
|---|
| 3654 | 1.0.5 (+ 2 patches) 10005
|
|---|
| 3655 | 1.0.5a-d 10006
|
|---|
| 3656 | 1.0.5e-r 10100 (not source compatible)
|
|---|
| 3657 | 1.0.5s-v 10006 (not binary compatible)
|
|---|
| 3658 | 1.0.6 (+ 3 patches) 10006 (still binary incompatible)
|
|---|
| 3659 | 1.0.6d-f 10007 (still binary incompatible)
|
|---|
| 3660 | 1.0.6g 10007
|
|---|
| 3661 | 1.0.6h 10007 10.6h (testing xy.z so-numbering)
|
|---|
| 3662 | 1.0.6i 10007 10.6i
|
|---|
| 3663 | 1.0.6j 10007 2.1.0.6j (incompatible with 1.0.0)
|
|---|
| 3664 | 1.0.7beta11-14 DLLNUM 10007 2.1.0.7beta11-14 (binary compatible)
|
|---|
| 3665 | 1.0.7beta15-18 1 10007 2.1.0.7beta15-18 (binary compatible)
|
|---|
| 3666 | 1.0.7rc1-2 1 10007 2.1.0.7rc1-2 (binary compatible)
|
|---|
| 3667 | 1.0.7 1 10007 (still compatible)
|
|---|
| 3668 | ...
|
|---|
| 3669 | 1.0.19 10 10019 10.so.0.19[.0]
|
|---|
| 3670 | ...
|
|---|
| 3671 | 1.0.64 10 10064 10.so.0.64[.0]
|
|---|
| 3672 | 1.2.54 13 10254 12.so.0.54[.0]
|
|---|
| 3673 |
|
|---|
| 3674 | Henceforth the source version will match the shared-library minor
|
|---|
| 3675 | and patch numbers; the shared-library major version number will be
|
|---|
| 3676 | used for changes in backward compatibility, as it is intended. The
|
|---|
| 3677 | PNG_PNGLIB_VER macro, which is not used within libpng but is available
|
|---|
| 3678 | for applications, is an unsigned integer of the form xyyzz corresponding
|
|---|
| 3679 | to the source version x.y.z (leading zeros in y and z). Beta versions
|
|---|
| 3680 | were given the previous public release number plus a letter, until
|
|---|
| 3681 | version 1.0.6j; from then on they were given the upcoming public
|
|---|
| 3682 | release number plus "betaNN" or "rcNN".
|
|---|
| 3683 |
|
|---|
| 3684 | .SH "SEE ALSO"
|
|---|
| 3685 | .IR libpngpf(3) ", " png(5)
|
|---|
| 3686 | .LP
|
|---|
| 3687 | .IR libpng :
|
|---|
| 3688 | .IP
|
|---|
| 3689 | http://libpng.sourceforge.net (follow the [DOWNLOAD] link)
|
|---|
| 3690 | http://www.libpng.org/pub/png
|
|---|
| 3691 |
|
|---|
| 3692 | .LP
|
|---|
| 3693 | .IR zlib :
|
|---|
| 3694 | .IP
|
|---|
| 3695 | (generally) at the same location as
|
|---|
| 3696 | .I libpng
|
|---|
| 3697 | or at
|
|---|
| 3698 | .br
|
|---|
| 3699 | ftp://ftp.info-zip.org/pub/infozip/zlib
|
|---|
| 3700 |
|
|---|
| 3701 | .LP
|
|---|
| 3702 | .IR PNG specification: RFC 2083
|
|---|
| 3703 | .IP
|
|---|
| 3704 | (generally) at the same location as
|
|---|
| 3705 | .I libpng
|
|---|
| 3706 | or at
|
|---|
| 3707 | .br
|
|---|
| 3708 | ftp://ftp.rfc-editor.org:/in-notes/rfc2083.txt
|
|---|
| 3709 | .br
|
|---|
| 3710 | or (as a W3C Recommendation) at
|
|---|
| 3711 | .br
|
|---|
| 3712 | http://www.w3.org/TR/REC-png.html
|
|---|
| 3713 |
|
|---|
| 3714 | .LP
|
|---|
| 3715 | In the case of any inconsistency between the PNG specification
|
|---|
| 3716 | and this library, the specification takes precedence.
|
|---|
| 3717 |
|
|---|
| 3718 | .SH AUTHORS
|
|---|
| 3719 | This man page: Glenn Randers-Pehrson
|
|---|
| 3720 | <glennrp at users.sourceforge.net>
|
|---|
| 3721 |
|
|---|
| 3722 | The contributing authors would like to thank all those who helped
|
|---|
| 3723 | with testing, bug fixes, and patience. This wouldn't have been
|
|---|
| 3724 | possible without all of you.
|
|---|
| 3725 |
|
|---|
| 3726 | Thanks to Frank J. T. Wojcik for helping with the documentation.
|
|---|
| 3727 |
|
|---|
| 3728 | Libpng version 1.2.54 - November 12, 2015:
|
|---|
| 3729 | Initially created in 1995 by Guy Eric Schalnat, then of Group 42, Inc.
|
|---|
| 3730 | Currently maintained by Glenn Randers-Pehrson (glennrp at users.sourceforge.net).
|
|---|
| 3731 |
|
|---|
| 3732 | Supported by the PNG development group
|
|---|
| 3733 | .br
|
|---|
| 3734 | png-mng-implement at lists.sf.net
|
|---|
| 3735 | (subscription required; visit
|
|---|
| 3736 | png-mng-implement at lists.sourceforge.net (subscription required; visit
|
|---|
| 3737 | https://lists.sourceforge.net/lists/listinfo/png-mng-implement
|
|---|
| 3738 | to subscribe).
|
|---|
| 3739 |
|
|---|
| 3740 | .SH NOTICES:
|
|---|
| 3741 |
|
|---|
| 3742 | This copy of the libpng notices is provided for your convenience. In case of
|
|---|
| 3743 | any discrepancy between this copy and the notices in the file png.h that is
|
|---|
| 3744 | included in the libpng distribution, the latter shall prevail.
|
|---|
| 3745 |
|
|---|
| 3746 | COPYRIGHT NOTICE, DISCLAIMER, and LICENSE:
|
|---|
| 3747 |
|
|---|
| 3748 | If you modify libpng you may insert additional notices immediately following
|
|---|
| 3749 | this sentence.
|
|---|
| 3750 |
|
|---|
| 3751 | This code is released under the libpng license.
|
|---|
| 3752 |
|
|---|
| 3753 | libpng versions 1.0.7, July 1, 2000, through 1.2.54, November 12, 2015, are
|
|---|
| 3754 | Copyright (c) 2000-2002, 2004, 2006-2015 Glenn Randers-Pehrson, are
|
|---|
| 3755 | derived from libpng-1.0.6, and are distributed according to the same
|
|---|
| 3756 | disclaimer and license as libpng-1.0.6 with the following individuals
|
|---|
| 3757 | added to the list of Contributing Authors:
|
|---|
| 3758 |
|
|---|
| 3759 | Simon-Pierre Cadieux
|
|---|
| 3760 | Eric S. Raymond
|
|---|
| 3761 | Cosmin Truta
|
|---|
| 3762 | Gilles Vollant
|
|---|
| 3763 |
|
|---|
| 3764 | and with the following additions to the disclaimer:
|
|---|
| 3765 |
|
|---|
| 3766 | There is no warranty against interference with your enjoyment of the
|
|---|
| 3767 | library or against infringement. There is no warranty that our
|
|---|
| 3768 | efforts or the library will fulfill any of your particular purposes
|
|---|
| 3769 | or needs. This library is provided with all faults, and the entire
|
|---|
| 3770 | risk of satisfactory quality, performance, accuracy, and effort is with
|
|---|
| 3771 | the user.
|
|---|
| 3772 |
|
|---|
| 3773 | libpng versions 0.97, January 1998, through 1.0.6, March 20, 2000, are
|
|---|
| 3774 | Copyright (c) 1998-2000 Glenn Randers-Pehrson, are derived from
|
|---|
| 3775 | libpng-0.96, and are distributed according to the same disclaimer and
|
|---|
| 3776 | license as libpng-0.96, with the following individuals added to the list
|
|---|
| 3777 | of Contributing Authors:
|
|---|
| 3778 |
|
|---|
| 3779 | Tom Lane
|
|---|
| 3780 | Glenn Randers-Pehrson
|
|---|
| 3781 | Willem van Schaik
|
|---|
| 3782 |
|
|---|
| 3783 | libpng versions 0.89, June 1996, through 0.96, May 1997, are
|
|---|
| 3784 | Copyright (c) 1996-1997 Andreas Dilger, are derived from libpng-0.88,
|
|---|
| 3785 | and are distributed according to the same disclaimer and license as
|
|---|
| 3786 | libpng-0.88, with the following individuals added to the list of
|
|---|
| 3787 | Contributing Authors:
|
|---|
| 3788 |
|
|---|
| 3789 | John Bowler
|
|---|
| 3790 | Kevin Bracey
|
|---|
| 3791 | Sam Bushell
|
|---|
| 3792 | Magnus Holmgren
|
|---|
| 3793 | Greg Roelofs
|
|---|
| 3794 | Tom Tanner
|
|---|
| 3795 |
|
|---|
| 3796 | libpng versions 0.5, May 1995, through 0.88, January 1996, are
|
|---|
| 3797 | Copyright (c) 1995-1996 Guy Eric Schalnat, Group 42, Inc.
|
|---|
| 3798 |
|
|---|
| 3799 | For the purposes of this copyright and license, "Contributing Authors"
|
|---|
| 3800 | is defined as the following set of individuals:
|
|---|
| 3801 |
|
|---|
| 3802 | Andreas Dilger
|
|---|
| 3803 | Dave Martindale
|
|---|
| 3804 | Guy Eric Schalnat
|
|---|
| 3805 | Paul Schmidt
|
|---|
| 3806 | Tim Wegner
|
|---|
| 3807 |
|
|---|
| 3808 | The PNG Reference Library is supplied "AS IS". The Contributing Authors
|
|---|
| 3809 | and Group 42, Inc. disclaim all warranties, expressed or implied,
|
|---|
| 3810 | including, without limitation, the warranties of merchantability and of
|
|---|
| 3811 | fitness for any purpose. The Contributing Authors and Group 42, Inc.
|
|---|
| 3812 | assume no liability for direct, indirect, incidental, special, exemplary,
|
|---|
| 3813 | or consequential damages, which may result from the use of the PNG
|
|---|
| 3814 | Reference Library, even if advised of the possibility of such damage.
|
|---|
| 3815 |
|
|---|
| 3816 | Permission is hereby granted to use, copy, modify, and distribute this
|
|---|
| 3817 | source code, or portions hereof, for any purpose, without fee, subject
|
|---|
| 3818 | to the following restrictions:
|
|---|
| 3819 |
|
|---|
| 3820 | 1. The origin of this source code must not be misrepresented.
|
|---|
| 3821 |
|
|---|
| 3822 | 2. Altered versions must be plainly marked as such and must not
|
|---|
| 3823 | be misrepresented as being the original source.
|
|---|
| 3824 |
|
|---|
| 3825 | 3. This Copyright notice may not be removed or altered from any
|
|---|
| 3826 | source or altered source distribution.
|
|---|
| 3827 |
|
|---|
| 3828 | The Contributing Authors and Group 42, Inc. specifically permit, without
|
|---|
| 3829 | fee, and encourage the use of this source code as a component to
|
|---|
| 3830 | supporting the PNG file format in commercial products. If you use this
|
|---|
| 3831 | source code in a product, acknowledgment is not required but would be
|
|---|
| 3832 | appreciated.
|
|---|
| 3833 |
|
|---|
| 3834 | END OF COPYRIGHT NOTICE, DISCLAIMER, and LICENSE.
|
|---|
| 3835 |
|
|---|
| 3836 | A "png_get_copyright" function is available, for convenient use in "about"
|
|---|
| 3837 | boxes and the like:
|
|---|
| 3838 |
|
|---|
| 3839 | printf("%s", png_get_copyright(NULL));
|
|---|
| 3840 |
|
|---|
| 3841 | Also, the PNG logo (in PNG format, of course) is supplied in the
|
|---|
| 3842 | files "pngbar.png" and "pngbar.jpg (88x31) and "pngnow.png" (98x31).
|
|---|
| 3843 |
|
|---|
| 3844 | Libpng is OSI Certified Open Source Software. OSI Certified Open Source is
|
|---|
| 3845 | a certification mark of the Open Source Initiative. OSI has not addressed
|
|---|
| 3846 | the additional disclaimers inserted at version 1.0.7.
|
|---|
| 3847 |
|
|---|
| 3848 | Glenn Randers-Pehrson
|
|---|
| 3849 | glennrp at users.sourceforge.net
|
|---|
| 3850 | November 12, 2015
|
|---|
| 3851 |
|
|---|
| 3852 | .\" end of man page
|
|---|
| 3853 |
|
|---|
