README
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- 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://ftp.simplesystems.org/pub/libpng/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