The zopfliPNG program does do bit depth reduction if that's possible. It even tests to see if a given small image that would be possible to bit depth reduce wou

The zopfliPNG program does do bit depth reduction if that's possible. It even tests to see if a given small image that would be possible to bit depth reduce would actually be smaller by it keeping 32 bit, since the added pallet overhead may cost more than the gain of a smaller pixel storage cost.