Are there any open source sprite format?

PNG just plainly sucks. I has no support for animations, timing or delta compression and sequence names. Also, PNG is slow at random access (you have to decompress image before use). Proprietary formats (like Diablo 2 DCC) are much better, but highly specialized for their games: some have no true color, other have no directions.

>>9
That only made sense when machines had 16MB or less of RAM. Last time I checked, my phone had 512MB of RAM and it costs $120 for a 16GB kit of desktop DDR3 at 1600MHz. Might as well use that RAM to increase performance and decrease power consumption, as well as simplify your source code.