[schmich]

Our team used pngquant (http://pngquant.org/) recently to reduce complex, high-res PNGs to about 33% of their original size. It gave us the size benefits of lossy compression while retaining the PNG alpha channel. It seems to be good enough to tide us over until WebP gains traction (not holding my breath).

[tracker1]

IIRC, you're limited to 256 colors total (including those with an alpha channel)... it works pretty well, but it really depends on the picture in question. I use pngquant all the time myself... :-)

[ashmud]

Color quantizer (http://x128.ho.ua/color-quantizer.html) lets you use up to 12-bit (4096 colors). For command line, the author has TruePNG (http://x128.ho.ua/pngutils.html).

[mark-r]

That's interesting, since there isn't a 12-bit PNG format. Do they leave it in 24 bit then, and just rely on better compression due to fewer unique bit combinations?

[ashmud]

It looks that way. Irfanview reports 24bpp for images saved when I selected > 256 colors in CQ.