Oh, could it really be that simple?

http://en.wikipedia.org/wiki/JPEG#Encoding is not something I've ever been especially familiar with, but as I poke further into the code that processes the title screen "tree" image, the two are looking strikingly similar.  Could this entire mess simply be an off-the-shelf JPEG processing algorithm tweaked for SNES? 

It sure would explain the JPEG-like artifacts visible if you zoom into the image.