The "PNG crunch" programs out there - eg OptiPNG - actually do a bit more work. They'll try palette-ising a truecolor image, applying all the PNG filters (http:

The "PNG crunch" programs out there - eg OptiPNG - actually do a bit more work. They'll try palette-ising a truecolor image, applying all the PNG filters (http://www.w3.org/TR/PNG-Filters.html http://www.w3.org/TR/PNG-Filters.html), etc. They also tend to use forked versions of zlib, often to expose some more internal knobs to trial-and-error on, so a zlib-compatible wrapper around zopfli wouldn't necessarily just drop in. But I'm sure support for zopfli will appear sooner rather than later :)