Dear Maintainer,
pnqnq is dead for years now and has a longstanding open bug that cripples
its usefulness. But there's a fork that's alive and has a fix for this,
among plenty other improvements:
https://sf.net/projects/pngnqs9
pngnq puts redundant colors into the palette, i.e. it uses less than the
requested number of colors to quantize to and produces inferior visual
quality. This questions the usefulness of pngnq since the only point in
using it is some smaller improvement in visual quality brought by its novel
algorithm.
See bug #10 from 2010:
https://sf.net/p/pngnq/bugs/10
If not switching to pngnq-s9 altogether, it would be nice to at least
incorporate their fix for described bug.