pngnq-s9
A modified pngnq: convert png images to 256 colours.
... weight to specific colour components when quantizing. The program also includes a few bug fixes relative to the most recent version of pngnq.
The .tar.gz files have been known to compile on Unix type systems, including Cygwin. The only external dependencies are libpng and zlib.
For Windows users, we have a 32 bit binary, in pngnq-s9-2.0.2.zip, that should run as is on most modern Windows machines.