1 PngMinus 2 -------- 3 (copyright Willem van Schaik, 1999) 4 5 6 License 7 ------- 8 9 Permission to use, copy, modify, and distribute this software and 10 its documentation for any purpose and without fee is hereby granted, 11 provided that the above copyright notice appear in all copies and 12 that both that copyright notice and this permission notice appear in 13 supporting documentation. This software is provided "as is" without 14 express or implied warranty. 15 16 17 Some history 18 ------------ 19 Soon after the creation of PNG in 1995, the need was felt for a set of 20 pnmtopng / pngtopnm utilities. Independantly Alexander Lehmann and I 21 (Willem van Schaik) started such a project. Luckily we discovered this 22 and merged the two together into pnmtopng.tar.gz, which is available 23 from a/o ftp://ftp.simplesystems.org/pub/libpng/png/. 24 25 These two utilities have many, many options and make use of most of the 26 features of PNG, like gamma, alpha, sbit, text-chunks, etc. This makes 27 the utilities quite complex and by now not anymore very maintainable. 28 When we wrote these programs, libpng was still in an early stage. 29 Therefore, lots of the functionality that we put in our software can now 30 be done using transform-functions in libpng. 31 32 Finally, to compile these programs, you need to have installed and 33 compiled three libraries: libpng, zlib and netpbm. Especially the latter 34 makes the whole setup a bit bulky. But that's unavoidable given the many 35 features of pnmtopng. 36 37 38 What now 39 -------- 40 At this moment libpng is in a very stable state and can do much of the 41 work done in pnmtopng. Also, pnmtopng needs to be upgraded to the new 42 interface of libpng. Hence, it is time for a rewrite from the ground up 43 of pnmtopng and pngtopnm. This will happen in the near future (stay 44 tuned). The new package will get a different name to distinguish it from 45 the old one: PngPlus. 46 47 To experiment a bit with the new interface of libpng, I started off with 48 a small prototype that contains only the basic functionality. It doesn't 49 have any of the options to read or write special chunks and it will do 50 no gamma correction. But this makes it also a simple program that is 51 quite easy to understand and can serve well as a template for other 52 software developments. (By now there are of course a couple of programs, 53 like Greg Roelofs' rpng/wpng, that can be used just as good.) 54 55 56 Can and can not 57 --------------- 58 As this is the small brother of the future PngPlus, I called this fellow 59 PngMinus. Because I started this development in good-old Turbo-C, I 60 avoided the use the netpbm library, which requires DOS extenders. Again, 61 another reason to call it PngMinus (minus netpbm :-). So, part of the 62 program are some elementary routines to read / write pgm- and ppm-files. 63 It does not read b&w pbm-files. 64 65 The downside of this approach is that you can not use them on images 66 that require blocks of memory bigger than 64k (the DOS version). For 67 larger images you will get an out-of-memory error. 68 69 As said before, PngMinus doesn't correct for gamma. When reading 70 png-files you can do this just as well by piping the output of png2pnm 71 to pnmgamma, one of the standard PbmPlus tools. This same scenario will 72 most probably also be followed in the full-blown future PngPlus, with 73 the addition of course of the possibility to create gamma-chunks when 74 writing png-files. 75 76 On the other hand it supports alpha-channels. When reading a png-image 77 you can write the alpha-channel into a pgm-file. And when creating an 78 RGB+A png-image, you just combine a ppm-file with a corresponding 79 pgm-file containing the alpha-channel. When reading, transparency chunks 80 are converted into an alpha-channel and from there on treated the same 81 way. 82 83 Finally you can opt for writing ascii or binary pgm- and ppm-files. When 84 the bit-depth is 16, the format will always be ascii. 85 86 87 Using it 88 -------- 89 To distinguish them from pnmtopng and PngPlus, the utilities are named 90 png2pnm and pnm2png (2 instead of to). The input- and output-files can 91 be given as parameters or through redirection. Therefore the programs 92 can be part of a pipe. 93 94 To list the options type "png2pnm -h" or "pnm2png -h". 95 96 97 Just like Scandinavian furniture 98 -------------------------------- 99 You have to put it together yourself. I did test the software under 100 MS-DOS with Turbo-C 3.0 and under RedHat Linux 4.2 with gcc. In both 101 cases I used libpng-1.0.4 and zlib-1.1.3. Later versions should be OK, 102 however some older libpng versions have a bug in pngmem.c when using 103 Turbo-C 3.0 (see below). 104 105 You can build it using one of the two makefiles (make -f makefile.###) 106 or use the batch/script files pngminus.bat / pngminus.sh. This assumes 107 that you have built the libraries in ../libpng and ../zlib. Using Linux, 108 make sure that you have built libpng with makefile.std and not 109 makefile.linux (also called .lnx in earlier versions of libpng). The 110 latter creates a .so shared-library, while the PngMinus makefile assumes 111 a normal .a static library. 112 113 If you create a ../pngsuite directory and then store the basn####.png 114 files from PngSuite (http://www.schaik.com/pngsuite/) in there, you can 115 test in one go the proper functioning of PngMinus, see png2pnm.bat and 116 pnm2png.bat (or the .sh versions). 117 118 119 Warranty 120 ------- 121 Please, remember that this was just a small experiment to learn a few 122 things. It will have many unforeseen features <vbg>. Who said bugs? Use 123 it when you are in need for something simple or when you want to start 124 developing your own stuff. 125 126 127 The Turbo bug 128 ------------- 129 ** pngmem.old 130 hptr = (png_byte huge *)((long)(hptr) & 0xfffffff0L); 131 hptr += 16L; 132 ** pngmem.c 133 hptr = (png_byte huge *)((long)(hptr) & 0xfffffff0L); 134 hptr = hptr + 16L; 135 ** 136 137 ** pngmem.old 138 png_ptr->offset_table_ptr[i] = (png_bytep)hptr; 139 hptr += (png_uint_32)65536L; 140 ** pngmem.c 141 png_ptr->offset_table_ptr[i] = (png_bytep)hptr; 142 hptr = hptr + 65536L; 143 ** 144 145 146 The end 147 ------- 148 Willem van Schaik 149 mailto:willem at schaik.com 150 http://www.schaik.com/png/ 151 ------- 152 Oct 1999 153 154
