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There is a collection of function definitions under the title
"Interface Definitions for libpng12" at
L<https://refspecs.linuxbase.org/LSB_4.0.0/LSB-Desktop-generic/LSB-Desktop-generic/libpng12man.html>
as part of the "Linux Standard Base Desktop Specification". These
contain extensive information on the prototypes and return values for
the libpng routines, something which is often only available elsewhere
by actually looking at the libpng source code. These pages are usually
the first hits on search engines if you search for a function name in
libpng.

=back

=head2 zlib documentation

See L<https://zlib.net/manual.html> for the zlib documentation.

=head2 Other Perl modules on CPAN

These other modules may also be useful.

=over

=item Alien::PNG

L<Alien::PNG> claims to be a way of "building, finding and using PNG
binaries". It may help in installing libpng. We didn't use it as a
dependency for this module because it seems not to work in batch mode,
but stop and prompt the user. We're interested in hearing feedback
from users whether this works or not on various platforms.

=item Imager

L<Imager>, L<Imager::Files> and C<Imager::Files::PNG> contain support
for reading and writing PNGs via libpng, as well as support for
reading and writing various other kinds of image files, changing the
images, converting, and more.

=item Image::ExifTool

L<Image::ExifTool> is a pure Perl (doesn't require a C compiler)
solution for accessing the text segments of images. It supports PNG
text segments.

=item Image::Info

L<Image::Info> gets information out of images. It supports PNG and is
written in pure Perl, so it doesn't require a C compiler. As well as
basics such as height, width, and colour type, it can get text chunks,
modification time, palette, gamma (gAMA chunk), resolution (pHYs
chunk), and significant bits (sBIT chunk). At the time of writing
(version 1.31) it doesn't support other chunks.

=item Image::PNG::Rewriter

L<Image::PNG::Rewriter> is a utility for unpacking and recompressing
the IDAT (image data) part of a PNG image. The main purpose seems to
be to recompress the image data with the module author's other module
L<Compress::Deflate7>. At the time of writing, that only works with
Perl versions 5.12 or later.

=item Image::Pngslimmer

L<Image::Pngslimmer> reduces the size of dynamically created PNG
images. It's very, very slow at reading PNG data, but seems to work
OK.

=item Image::PNG::Write::BW

L<Image::PNG::Write::BW> writes black and white PNGs from strings.

=item Image::Size

If you only need to read the sizes of images, L<Image::Size> works
with PNG and other image formats.

=back




=head1 AUTHOR

Ben Bullock, <benkasminbullock@gmail.com>

=head1 COPYRIGHT & LICENCE

This package and associated files are copyright (C) 
2011-2026
Ben Bullock.

You can use, copy, modify and redistribute this package and associated
files under the Perl Artistic Licence or the GNU General Public
Licence.