Editing Sonic R
Taken from www.Segasonic.net

Get an editor that can read RAW files, like Paint Shop Pro.

Search where Sonic R is installed for RAW files. Most can be found in the GENERAL and BIN folders.

Open them up. When it asks for the dimensions, etc. to use for reading the file, choose the following:

Image Size:

640x480 or 256x256 (some are different sizes you'll have to toy with it)

Color Channels:

Three Channel (RBG)

File Structure:

Interleaved (RGB RGB....)

Order RGB

Make sure "Flipped: bottom up" is UNCHECKED

Hit okay, edit the file like you want, then save. be sure to make backups!!