Currently, I'm just upscaling the newer gamecube textures. Interestingly, in the stages that have posters and advertisements (like City Escape), almost all of them were changed to new designs for SA2 Battle. I'm then using those textures as a base to upscale and/or edit. So, I'm going through and taking particularly bad or important textures from the gamecube release and replacing them with their Dreamcast equivalents that don't have all of the compression artifacts. The gamecube's original resolution actually helped to hide many of the blemishes, but fast-forward to HD+ resolutions in dolphin and it's easy to see how bad some things look. While many environment textures aren't too bad, smaller and complex textures have horrible color and pattern artifacting. When Sega ported Sonic Adventure 2 over to the gamecube, whoever was in charge of converting the textures used some horrible, lossy compression in order to fit everything onto the gamecube's smaller capacity disc ( whoops).
