I could be mistaken, if it was SF II or some other similar game, but for PC (back in the DOS game, the sprites for these were not stored rectangular (with transparency) but rather a run-length of here is a line of pixels that starts from here to here. Hence your code can just "movsb" instead of checking (expensive) for transparency).
... Could've been another game, but it was fun trying to decode the images :)
(I think it also makes pixel to pixel collision easier to tackle, but don't remember the details - this might've been Star Control II thing, another game we used (as kids) to decode images/mods)
This reminds me: the Allegro library has a way to compile bitmaps into series of mov instructions to make blitting faster. This was somehow the fastest method on early x86 processors. Loops were expensive back then.
Perhaps you were thinking of SFIBM/SF2IBM, aka SFLIU [1], a homebrew version of SF2 for PCs written by a Korean dev. There were specs of the file formats used out on the internet at the time and I remember the image files were stored as run-length encoding.
You might be right (for my case). It could've been that is what I've played (!!!) it was around 1991-1996 (?) and it's when I've started digging into the format (along with other games, like SC2). Might've been even later, but it was an older game. Never knew it was a homebrew version :)
... Could've been another game, but it was fun trying to decode the images :)
(I think it also makes pixel to pixel collision easier to tackle, but don't remember the details - this might've been Star Control II thing, another game we used (as kids) to decode images/mods)