Keith,

A bitmap which uses only 2 colors is stored as a 1 bpp bitmap, a bitmap which uses 3 or 4 colors is stored as a 2 bpp bitmap. Therefore, you can save memory by reducing the number of colors used in a bitmap. Note that 2 color bitmaps contain a tiny clut so it doesn't matter which colors you pick (i.e. it doesn't have to be black and white).

Something else to consider is that in a CCF the lines in both 1 and 2 bpp bitmaps are padded at the end so they always contain a multiple of 8 pixels (i.e. 8 bit for a 1 bpp bitmap and 16 bit for a 2 bpp bitmap). Therefore you may want to avoid using e.g. 9 pixel wide bitmaps.

Regards,

Jan