WMFs are vector files, which means that they store mathematical formulas about how an image should be displayed on a screen. One major benefit of this format is that it provides scalability without the loss of image quality. WMF files do not become jumbled or jagged as we zoom in or out on them.
BMPs are raster files, which means that they store information about each pixel on an image. Although bitmaps can render rich, photo-quality images, they become jumbled when we zoom in or jagged when we zoom out.
Creating user defined bitmaps for menu
When creating bitmaps for use on the System Architect menu, note that the top‑left pixel of any bitmap sets the mask color. Whatever that color pixel is set to, determines what color will be made to mask to the background color of the menu; in other words, become invisible. This enables you to create sophisticated bitmaps with hollow areas.
To create a bitmap that is a square, make the square 14x14 pixels, so that the outer, top‑left pixel is a different color from than the perimeter of the square.