Image::Pngslimmer version 0.26
=============================

OVERVIEW

Image::Pngslimmer reduces the size of PNGs by removing non-critcal chunks and
recompressing, filtering or palettizing images.

Other tools, such as pngcrush (http://pmt.sourceforge.net/pngcrush/) 
will deliver better results for static PNGs and Image::Pnglimmer 
was orginally designed for dynamically created PNGs.

use Image::Pngslimmer

Image::Pngslimmer::ispng($blob) - returns 1 if the BLOB conforms to the
structure for a PNG and that all CRCs are correct.

Image::Pngslimmer::discard_noncritical($blob) - returns a BLOB stripped of any
non-critcal chunks. If the passed-in BLOB does not conform to the basic structure
of a PNG the returned BLOB is identical to the passed-in BLOB. The passed in BLOB
is not altered by this function.

Image::Pngslimmer::analyze($blob) - after calling Image::Pngslimmer::ispng($blob)
this will iterate through the chunks in the supplied byte stream represented by 
$blob and return an array of strings describing the chunks in the PNG. It can be
useful for testing the "before and after" effect of discard_noncritical($blob).

Image::Pngzlimmer::zlibshrink($blob) will attempt to improve compression of the supplied BLOB

Image::Pngslimmer::filter($blob) will attempt to apply adaptive filtering for
better compression of the supplied BLOB - filtering normally results in better
compression once zlibshrink() is reapplied if the original image is truecolour.

Image::Pngslimmer::indexcolours($blob) will attempt to losslessly convert the supplied PNG to
a colour indexed image - of the image contains more than 256 colours this will not work and the
original PNG is returned instead.

Image::Pngslimmer::palettize($blob[, $colours[, $dither]]) will colour index (with a PLTE chunk) 
a 24 bit RGB image. If the original image has 256 colours or less it will do this losslessly by 
calling indexcolours(), otherwise it will generate a palette by using the median cut algorithm.
The size of the palette can be set by the optional $colours in the range 1 - 256 (the defult 0 
gives 256 colours). If the optional $dither is set to 1, then the output image will be dithered
but please note the current dithering algorithm is EXTREMELY SLOW and should be avoided.

NB: Alpha channels in the original image will be lost with with quantization or indexation.


Image::Pngslimmer::reportcolours($blob) will print details of the colour frequencies in the
passed in PNG.


INSTALLATION

To install this module type the following:

   perl Makefile.PL
   make
   make test
   make install

DEPENDENCIES


POSIX
Compress::Zlib
Compress::Raw::Zlib
  

COPYRIGHT AND LICENCE


Copyright (C) 2006, 2007i, 2008 by Adrian McMenamin <adrian AT mcmen DOT demon DOT co DOT uk>

This library is free software; you can redistribute it and/or modify
it under the same terms as Perl itself, either Perl version 5.8.4 or,
at your option, any later version of Perl 5 you may have available.


