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I am very new to this whole situation, but I came across a Pokemon Yellow disassembly and I am trying to modify the title screen. The problem is that the sprite is stored as a .2bpp file, which is unrecognizable to most programs. I have tried to find 2bpp editors, but they only seem to be add-ons to other programs such as GIMP, which would be find, but it's an out of date version, and I can't find that version of GIMP (2.0.0, I think). Any other programs seem to not accept 2bpp files, and only accept .gbc or .nes files, which seems to be the ROMs themselves. So, I still can't edit the sprite.
Each .2bpp file also comes with a .png version, which I can open, edit, and save, and then rename as a .2bpp file, but whenever I compile the ROM, the screen looks like pure gibberish. I assume this is because the .png -> .2bpp process doesn't compress/convert it properly the way a .2bpp editor woud. (To clarify on this, I started with a clean build that works, moved the "yellow_titlescreen.2bpp" file away from the folder, renamed the "yellow_titlescreen.png" to "yellow_titlescreen.2bpp" [I haven't edited anything at this point], and recompiled, and it's still broken. So I know I didn't just ruin the image when I edited it, because in this case, I didn't edit it.)
Can anyone help me solve this? I don't need it to interpret the sprite in a readable way, I can find what I need to change and change it no matter what it looks like, I just need to actually be able to change it and see those changes working in a way that doesn't break it.