The "Bitmaps" window allos view and replacement of single-bitmaps of the game.
Some bitmaps may be localized and would require a replacement for each language.
Although supported, the main game doesn't make use of this: The MFD images of French or German still have English text on them.
When exporting, these images are written as
.png files with a palette and a transparency flag.
For importing, refer to Import Processors for conversion rules.
"Clearing" a bitmap replaces it with a 1x1 transparent image. "Removing" a bitmap removes the entry from the mod.