Bitmaps are handled by the CFbsBitmap class, which provides facilities for creating, loading and saving bitmaps, and the TBitmapUtil class, which provides functions that allow the user to operate on the individual bits within a bitmap.
Each bitmap has two sizes stored with it: its twip-size—a "real-world" size used for WYSIWYG purposes, specified in twips; and its pixel-size—the actual size of the bitmap in pixels.