In my own experiments compressing pixel art, I found that gzipped .bmp files were smaller than the output of pngcrush just as often as they were larger. On aver

In my own experiments compressing pixel art, I found that gzipped .bmp files were smaller than the output of pngcrush just as often as they were larger. On average the pngs were slightly smaller, but you can tar together a whole bunch of similar bmps and gzip the lot, and then gzip really blows png out of the water. For a compressed file format specialised for images, I found png's performance very disappointing and decided not to use it.