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Pnmtopng and Pngtopnm are based on programs of the same name in the
Pnmtopng package owned by Alexander Lehmann and Willem Van Schaik,
available at http://www.libpng.org/pub/png/src on 2001.07.14.
I added it to and adapted it to Netpbm on 2000.03.02 to make it more
easily available to people. I applied a patch on 2000.06.03 to bring
it up the 2.37.4 release of that package. I updated it again on
2001.07.14 to bring it up to Release 2.37.5. There is no process in
place to bring improvements to the base package into the Netpbm
version, but there hasn't been a lot of update activity anyway.
Attached below is the file README from Release 2.37.5 of the base
package.
Here are the differences between the base and the Netpbm version:
I added an "unsigned" to make formal and actual arguments to png_sig_cmp()
match and quiet a compiler warning.
I fixed an "include" statement so the dependencies work out right.
I removed the BIGGRAYS stuff, which became obsolete in Netpbm 9.0
I replaced a PPM_MAXVAL with PPM_OVERALLMAXAL to handle the new 16 bits
formats.
macro VERSION is defined directly in pngtopnm.c and pnmtopng.c instead
of being included via file version.h.
Pnmtopng, since June 2001, reads one row at a time instead of holding
the entire image in memory. That makes it work with large bitmaps
where it would otherwise run out of memory. It also works faster with
bitmaps since a bit takes up only a bit of memory in a cached input
file, but 96 bits of memory after reading it into a Netpbm data
structure.
The base Pnmtopng ignores -transparent if it specifies a color that
isn't in the image. Netpbm's Pnmtopng selects a nearby color that _is_
in the image, which is what base Pnmtopng did before October 2000.
Netpbm's Pnmtopng lets you put an '=' sign before the color to specify
that you don't want a nearby color to be chosen, i.e. you want the
base Pnmtopng function. This is consistent with Pnmtogif.
There were some other changes necessary before Netpbm 9.0, but the change
of the xelval type from 1 byte to 4 made them unnecessary.
** PNMTOPNG / PNGTOPNM
** version 2.37.5 - 24 October 2000
[This is a semi-official bug-fix and enhancement release; I sort of took over
maintenance of this package while Willem was on an extended bike trip, and
for now I'm continuing with periodic, small updates. Version 2.37 (March
1998) was never publicly released, partly because Willem had hoped to quiet
gcc's "<var> might be clobbered by `longjmp'" warnings. Those are fixed in
2.37.2; under Solaris, they resulted in stack corruption even when there was
no error in the image files or libraries. Version 2.37.3 fixes a minor bug
w.r.t. error exits and generally does cleaner error exits (close files, etc.)
Version 2.37.4 fixes a bug that caused 16-shade grayscale images to be written
as 8-bit grayscale instead of (smaller) 4-bit colormapped images (bug report,
analysis and fix by Rafal Rzeczkowski), and it supports the new/upcoming
pbmplus release. Version 2.37.5 fixes a bug in -transparent handling (pnmtopng
no longer chooses an approximate color if the specified one isn't present) and
quiets a gcc warning in the non-16-bit version.
--Greg Roelofs]
The utilities pnmtopng and pngtopnm are based on other pbm tools and require
the libraries included in the pbmplus/netpbm package. Also required are the
png library and the zlib compression library.
These can be found at:
ftp://swrinde.nde.swri.edu/pub/png/src/libpng-*
ftp://swrinde.nde.swri.edu/pub/png/src/zlib-*
ftp://ftp.x.org/contrib/utilities/netpbm-1mar1994*
or see
http://www.libpng.org/pub/png/apps/pnmtopng.html
http://netpbm.sourceforge.net/
http://www.acme.com/software/pbmplus/ [update coming soon?]
To compile and install a makefile is provided. Do check the directories
where you have put the required libraries. Then either accommodate the
makefile or make links from generic names (e.g., zlib) to version-specific
directories (e.g., zlib-1.1.3), which is the recommended way.
For testing purposes, have a look at the test-set PngSuite.tar.gz, which
contains a small test-image for every PNG color type and for most PNG chunk
types. It can be found at:
http://www.schaik.com/pngsuite/pngsuite.html
ftp://swrinde.nde.swri.edu/pub/png/images/suite/
Other web pages with PNG images are at:
http://www.libpng.org/pub/png/png-textures.html
http://www.libpng.org/pub/png/pngs-img.html
http://www.libpng.org/pub/png/pngpic2.html
http://www.libpng.org/pub/png/colorcube/
http://www.libpng.org/pub/png/pngmisc.html#images
------
Alexander Lehmann <lehmann@usa.net>
Willem van Schaik <willem@schaik.com>
Greg Roelofs <newt@pobox.com>
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