| 1 | PngMinus
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| 2 | --------
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| 3 | (copyright Willem van Schaik, 1999)
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| 4 |
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| 5 |
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| 6 | License
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| 7 | -------
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| 8 |
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| 9 | Permission to use, copy, modify, and distribute this software and
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| 10 | its documentation for any purpose and without fee is hereby granted,
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| 11 | provided that the above copyright notice appear in all copies and
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| 12 | that both that copyright notice and this permission notice appear in
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| 13 | supporting documentation. This software is provided "as is" without
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| 14 | express or implied warranty.
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| 15 |
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| 16 |
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| 17 | Some history
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| 18 | ------------
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| 19 | Soon after the creation of PNG in 1995, the need was felt for a set of
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| 20 | pnmtopng / pngtopnm utilities. Independantly Alexander Lehmann and I
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| 21 | (Willem van Schaik) started such a project. Luckily we discovered this
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| 22 | and merged the two together into pnmtopng.tar.gz, which is available
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| 23 | from a/o ftp://ftp.simplesystems.org/pub/libpng/png/.
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| 24 |
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| 25 | These two utilities have many, many options and make use of most of the
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| 26 | features of PNG, like gamma, alpha, sbit, text-chunks, etc. This makes
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| 27 | the utilities quite complex and by now not anymore very maintainable.
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| 28 | When we wrote these programs, libpng was still in an early stage.
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| 29 | Therefore, lots of the functionality that we put in our software can now
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| 30 | be done using transform-functions in libpng.
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| 31 |
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| 32 | Finally, to compile these programs, you need to have installed and
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| 33 | compiled three libraries: libpng, zlib and netpbm. Especially the latter
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| 34 | makes the whole setup a bit bulky. But that's unavoidable given the many
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| 35 | features of pnmtopng.
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| 36 |
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| 37 |
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| 38 | What now
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| 39 | --------
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| 40 | At this moment libpng is in a very stable state and can do much of the
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| 41 | work done in pnmtopng. Also, pnmtopng needs to be upgraded to the new
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| 42 | interface of libpng. Hence, it is time for a rewrite from the ground up
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| 43 | of pnmtopng and pngtopnm. This will happen in the near future (stay
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| 44 | tuned). The new package will get a different name to distinguish it from
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| 45 | the old one: PngPlus.
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| 46 |
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| 47 | To experiment a bit with the new interface of libpng, I started off with
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| 48 | a small prototype that contains only the basic functionality. It doesn't
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| 49 | have any of the options to read or write special chunks and it will do
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| 50 | no gamma correction. But this makes it also a simple program that is
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| 51 | quite easy to understand and can serve well as a template for other
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| 52 | software developments. (By now there are of course a couple of programs,
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| 53 | like Greg Roelofs' rpng/wpng, that can be used just as good.)
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| 54 |
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| 55 |
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| 56 | Can and can not
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| 57 | ---------------
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| 58 | As this is the small brother of the future PngPlus, I called this fellow
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| 59 | PngMinus. Because I started this development in good-old Turbo-C, I
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| 60 | avoided the use the netpbm library, which requires DOS extenders. Again,
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| 61 | another reason to call it PngMinus (minus netpbm :-). So, part of the
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| 62 | program are some elementary routines to read / write pgm- and ppm-files.
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| 63 | It does not read b&w pbm-files.
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| 64 |
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| 65 | The downside of this approach is that you can not use them on images
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| 66 | that require blocks of memory bigger than 64k (the DOS version). For
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| 67 | larger images you will get an out-of-memory error.
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| 68 |
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| 69 | As said before, PngMinus doesn't correct for gamma. When reading
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| 70 | png-files you can do this just as well by piping the output of png2pnm
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| 71 | to pnmgamma, one of the standard PbmPlus tools. This same scenario will
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| 72 | most probably also be followed in the full-blown future PngPlus, with
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| 73 | the addition of course of the possibility to create gamma-chunks when
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| 74 | writing png-files.
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| 75 |
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| 76 | On the other hand it supports alpha-channels. When reading a png-image
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| 77 | you can write the alpha-channel into a pgm-file. And when creating an
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| 78 | RGB+A png-image, you just combine a ppm-file with a corresponding
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| 79 | pgm-file containing the alpha-channel. When reading, transparency chunks
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| 80 | are converted into an alpha-channel and from there on treated the same
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| 81 | way.
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| 82 |
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| 83 | Finally you can opt for writing ascii or binary pgm- and ppm-files. When
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| 84 | the bit-depth is 16, the format will always be ascii.
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| 85 |
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| 86 |
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| 87 | Using it
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| 88 | --------
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| 89 | To distinguish them from pnmtopng and PngPlus, the utilities are named
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| 90 | png2pnm and pnm2png (2 instead of to). The input- and output-files can
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| 91 | be given as parameters or through redirection. Therefore the programs
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| 92 | can be part of a pipe.
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| 93 |
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| 94 | To list the options type "png2pnm -h" or "pnm2png -h".
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| 95 |
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| 96 |
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| 97 | Just like Scandinavian furniture
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| 98 | --------------------------------
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| 99 | You have to put it together yourself. I did test the software under
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| 100 | MS-DOS with Turbo-C 3.0 and under RedHat Linux 4.2 with gcc. In both
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| 101 | cases I used libpng-1.0.4 and zlib-1.1.3. Later versions should be OK,
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| 102 | however some older libpng versions have a bug in pngmem.c when using
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| 103 | Turbo-C 3.0 (see below).
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| 104 |
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| 105 | You can build it using one of the two makefiles (make -f makefile.###)
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| 106 | or use the batch/script files pngminus.bat / pngminus.sh. This assumes
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| 107 | that you have built the libraries in ../libpng and ../zlib. Using Linux,
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| 108 | make sure that you have built libpng with makefile.std and not
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| 109 | makefile.linux (also called .lnx in earlier versions of libpng). The
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| 110 | latter creates a .so shared-library, while the PngMinus makefile assumes
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| 111 | a normal .a static library.
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| 112 |
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| 113 | If you create a ../pngsuite directory and then store the basn####.png
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| 114 | files from PngSuite (http://www.schaik.com/pngsuite/) in there, you can
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| 115 | test in one go the proper functioning of PngMinus, see png2pnm.bat and
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| 116 | pnm2png.bat (or the .sh versions).
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| 117 |
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| 118 |
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| 119 | Warranty
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| 120 | -------
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| 121 | Please, remember that this was just a small experiment to learn a few
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| 122 | things. It will have many unforeseen features <vbg>. Who said bugs? Use
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| 123 | it when you are in need for something simple or when you want to start
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| 124 | developing your own stuff.
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| 125 |
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| 126 |
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| 127 | The Turbo bug
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| 128 | -------------
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| 129 | ** pngmem.old
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| 130 | hptr = (png_byte huge *)((long)(hptr) & 0xfffffff0L);
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| 131 | hptr += 16L;
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| 132 | ** pngmem.c
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| 133 | hptr = (png_byte huge *)((long)(hptr) & 0xfffffff0L);
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| 134 | hptr = hptr + 16L;
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| 135 | **
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| 136 |
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| 137 | ** pngmem.old
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| 138 | png_ptr->offset_table_ptr[i] = (png_bytep)hptr;
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| 139 | hptr += (png_uint_32)65536L;
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| 140 | ** pngmem.c
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| 141 | png_ptr->offset_table_ptr[i] = (png_bytep)hptr;
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| 142 | hptr = hptr + 65536L;
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| 143 | **
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| 144 |
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| 145 |
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| 146 | The end
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| 147 | -------
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| 148 | Willem van Schaik
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| 149 | mailto:[email protected]
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| 150 | http://www.schaik.com/png/
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| 151 | -------
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| 152 | Oct 1999
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| 153 |
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