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 :)
[1] http://cwcyrix.nsupdate.info/archives/SFLIU/sfliu.html