PNGNQ - PNG NEUQUANT
VERSION 1.1

USAGE: 

  pngnq [-vfhV][-s sample factor][-e extension][-d dir][-n colours][-Q f|n][input files]
  options:
     -v Verbose mode. Prints status messages.
     -f Force ovewriting of files.
     -s Sample factor. The neuquant algorithm samples pixels stepping by this value.
     -n Number of colours the quantized image is to contain. Range: 2 to 256. Defaults to 256.
     -e Specifies the new filename extension. Defaults to -nq8.png. 
        Will drop .png from original filenames.
     -d Relocates the quantized files into this directory. 
        Otherwise output files stay in the same directory as the input files. 
     input files: The png files to be processed. Defaults to standard input if not specified.
     -Q Dithering method: f = Floyd Steinberg, n = None (default)
     -V Print version number and library versions.
     -h Print this help.

  Quantizes a 32-bit RGBA PNG image to an 8 bit RGBA palette PNG
  using the neuquant algorithm. The output file name is the input file name
  extended with "-nq8.png" or a specified extension.

NOTES:

Pngnq is a tool for quantizing PNG images in RGBA format.
Pngnq is an adaptation by Stuart Coyle of Greg Roelf's pnqquant program
using Anthony Dekker's neuquant algorithm.

Pngnq exists because I needed a lot of png images in RGBA format
to be quantized. After some searching, the only tool I could find
that worked was pngquant. I tried pngquant but found that the median
cut algorithm that it uses, with or without dithering, gave inferior
looking results to the neuquant algorithm. You can see the difference
demonstrated on the neuquant web page:  
http://members.ozemail.com.au/~dekker/NEUQUANT.HTML.

The program was written to fulfill the specific needs of the small
project I was working on, and as such does not have all the
functionality one could want.

I use Greg Roelf's png reading and writing code unchanged for the most part.
The pngnq source code includes neuquant32, which is an extension of Anthony Dekker's 
neuquant, to make it handle 4 channels of pixel data.

Major rewrite by Kornel Lesiński, adding double precision, dithering, better handling of alpha
transparency and more. Thanks!

This program has been tested on: 
	Linux 32 and 64 bit
	Mac OSX - intel processor.
	OpenBSD 32 bit
	Win32

REQUIREMENTS:
	Pngnq depends on the libpng and libz libraries.
	You will need libpng >=1.2.8 installed. 
	If you have this then you will have libz. 
  On windows you will require the libpng13.dll 
	which can be downloaded from several sites.

BUGS:
  Some problems with greyscale alpha images at low bit depths.
  
TODO list:

	I want to change the error measure to use CIE u' v' color
	space and see if results are visually better.

	Limited image input formats. I am not doing much checking on
	the image pixel depth etc.

	Do a detailed comparison with other quantization algortithms.
		-  the pngcomp tool is in development to do this.


Copyright (c) Stuart Coyle 2004-2009 stuart.coyle@gmail.com

See LICENCE for details of copyrights held on this program.