i'm actually sipping the sprites out of the arcade roms, via the tiledata.
Just to make it right, and as test, i'm extracting Damnd. This sprite has 40 positions, and for the moment, the iff file with its sprites is 376kb. i expect him to be something like
with all the sprites (i mean for example, the part of level 1 where Damnd is, you have 6 differents sprites, meaning that it's something like 6 or 7 * 350-450kb = around 3mb.
it's bigger in memory with sprites at bitmap instead of tiles. With tiles it would be less i guess.