PNGNQ - PNG NEUQUANT

USAGE: 

   pngnq [-v][-s sample factor] [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. Defaults to 3.
      input files: The png files to be processed. Defaults to standard input if not specified. 

   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"  


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.

Specifically the things that it lacks are:

	Can only quantize to 256 colors. Though It will drop to less
		if less colors are needed.

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

	No dithering. I am sure that it is not needed with this
	algorithm.

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

	This has not been tested on platforms other than GNU/Linux on
	an Intel machine. I might get around to a windows port...one day.


Copyright (c) Stuart Coyle 2004 stuart@cybertherial.com

See LICENCES for details of copyrights held on this program.
