Big and colorful images (e.g. About-Logos) usually take lots of space when stored in a traditional BitMap structure. To save memory, you can decide to have the picture compressed in your code and use the Bodychunk class instead of the Bitmap class for displaying. MUI will then automatically decompress your image when its about to appear in a window.
Since Bodychunk class is a subclass of Bitmap class, you can of course use all the Bitmaps remapping and transparency features.