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* Datasets becomes the new trunk and retires after that :-)
author mvbarracuda@33b003aa-7bff-0310-803a-e67f0ece8222
date Sun, 29 Jun 2008 18:44:17 +0000
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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@schaik.com
150 http://www.schaik.com/png/
151 -------
152 Oct 1999
153