I've recently translated a GBA game: Fullmetal Alchemist-Sonata of Memories. But there are some graphics that I still can't edit.
At first glance, they seem uncompressed. But there is code inserted in the middle of the graphic. I think these codes control the offset shifts between one tile and the next (not all tiles of the graphic are at the same offset).
It's better seen in the image below. On the left, it's the tile as it appears in-game. On the right, it's the tile in Tile Layer Pro.
As you can see, the code appears as strange pixels that aren't part of the actual graphic.
The problem is I can't delete those pixels without messing the entire graphic, and they often get in the way when drawing English letters.
Other than this, even when the tile is clean enough, the drawing may behave in unexpected ways. For example, pixels may appear mirrored, or shifted to the left in-game.
Anyone knows what's this about? Is it some kind of compression? I don't know how to get around this. I could edit some with much difficulty, but others seem impossible.