+++ /dev/null
-PngMinus
---------
-(copyright Willem van Schaik, 1999)
-
-
-License
--------
-
-Permission to use, copy, modify, and distribute this software and
-its documentation for any purpose and without fee is hereby granted,
-provided that the above copyright notice appear in all copies and
-that both that copyright notice and this permission notice appear in
-supporting documentation. This software is provided "as is" without
-express or implied warranty.
-
-
-Some history
-------------
-Soon after the creation of PNG in 1995, the need was felt for a set of
-pnmtopng / pngtopnm utilities. Independantly Alexander Lehmann and I
-(Willem van Schaik) started such a project. Luckily we discovered this
-and merged the two together into pnmtopng.tar.gz, which is available
-from a/o ftp://swrinde.nde.swri.edu/pub/png/.
-
-These two utilities have many, many options and make use of most of the
-features of PNG, like gamma, alpha, sbit, text-chunks, etc. This makes
-the utilities quite complex and by now not anymore very maintainable.
-When we wrote these programs, libpng was still in an early stage.
-Therefore, lots of the functionality that we put in our software can now
-be done using transform-functions in libpng.
-
-Finally, to compile these programs, you need to have installed and
-compiled three libraries: libpng, zlib and netpbm. Especially the latter
-makes the whole setup a bit bulky. But that's unavoidable given the many
-features of pnmtopng.
-
-
-What now
---------
-At this moment libpng is in a very stable state and can do much of the
-work done in pnmtopng. Also, pnmtopng needs to be upgraded to the new
-interface of libpng. Hence, it is time for a rewrite from the ground up
-of pnmtopng and pngtopnm. This will happen in the near future (stay
-tuned). The new package will get a different name to distinguish it from
-the old one: PngPlus.
-
-To experiment a bit with the new interface of libpng, I started off with
-a small prototype that contains only the basic functionality. It doesn't
-have any of the options to read or write special chunks and it will do
-no gamma correction. But this makes it also a simple program that is
-quite easy to understand and can serve well as a template for other
-software developments. (By now there are of course a couple of programs,
-like Greg Roelofs' rpng/wpng, that can be used just as good.)
-
-
-Can and can not
----------------
-As this is the small brother of the future PngPlus, I called this fellow
-PngMinus. Because I started this development in good-old Turbo-C, I
-avoided the use the netpbm library, which requires DOS extenders. Again,
-another reason to call it PngMinus (minus netpbm :-). So, part of the
-program are some elementary routines to read / write pgm- and ppm-files.
-It does not read b&w pbm-files.
-
-The downside of this approach is that you can not use them on images
-that require blocks of memory bigger than 64k (the DOS version). For
-larger images you will get an out-of-memory error.
-
-As said before, PngMinus doesn't correct for gamma. When reading
-png-files you can do this just as well by piping the output of png2pnm
-to pnmgamma, one of the standard PbmPlus tools. This same scenario will
-most probably also be followed in the full-blown future PngPlus, with
-the addition of course of the possibility to create gamma-chunks when
-writing png-files.
-
-On the other hand it supports alpha-channels. When reading a png-image
-you can write the alpha-channel into a pgm-file. And when creating an
-RGB+A png-image, you just combine a ppm-file with a corresponding
-pgm-file containing the alpha-channel. When reading, transparency chunks
-are converted into an alpha-channel and from there on treated the same
-way.
-
-Finally you can opt for writing ascii or binary pgm- and ppm-files. When
-the bit-depth is 16, the format will always be ascii.
-
-
-Using it
---------
-To distinguish them from pnmtopng and PngPlus, the utilities are named
-png2pnm and pnm2png (2 instead of to). The input- and output-files can
-be given as parameters or through redirection. Therefore the programs
-can be part of a pipe.
-
-To list the options type "png2pnm -h" or "pnm2png -h".
-
-
-Just like Scandinavian furniture
---------------------------------
-You have to put it together yourself. I did test the software under
-MS-DOS with Turbo-C 3.0 and under RedHat Linux 4.2 with gcc. In both
-cases I used libpng-1.0.4 and zlib-1.1.3. Later versions should be OK,
-however some older libpng versions have a bug in pngmem.c when using
-Turbo-C 3.0 (see below).
-
-You can build it using one of the two makefiles (make -f makefile.###)
-or use the batch/script files pngminus.bat / pngminus.sh. This assumes
-that you have built the libraries in ../libpng and ../zlib. Using Linux,
-make sure that you have built libpng with makefile.std and not
-makefile.linux (also called .lnx in earlier versions of libpng). The
-latter creates a .so shared-library, while the PngMinus makefile assumes
-a normal .a static library.
-
-If you create a ../pngsuite directory and then store the basn####.png
-files from PngSuite (http://www.schaik.com/pngsuite/) in there, you can
-test in one go the proper functioning of PngMinus, see png2pnm.bat and
-pnm2png.bat (or the .sh versions).
-
-
-Warranty
--------
-Please, remember that this was just a small experiment to learn a few
-things. It will have many unforeseen features <vbg>. Who said bugs? Use
-it when you are in need for something simple or when you want to start
-developing your own stuff.
-
-
-The Turbo bug
--------------
-** pngmem.old
- hptr = (png_byte huge *)((long)(hptr) & 0xfffffff0L);
- hptr += 16L;
-** pngmem.c
- hptr = (png_byte huge *)((long)(hptr) & 0xfffffff0L);
- hptr = hptr + 16L;
-**
-
-** pngmem.old
- png_ptr->offset_table_ptr[i] = (png_bytep)hptr;
- hptr += (png_uint_32)65536L;
-** pngmem.c
- png_ptr->offset_table_ptr[i] = (png_bytep)hptr;
- hptr = hptr + 65536L;
-**
-
-
-The end
--------
-Willem van Schaik
-mailto:willem@schaik.com
-http://www.schaik.com/png/
--------
-Oct 1999
-
projects / synfig.git / blobdiff