Color map image fader for graphics window subsystem

A color map image fader which lets a user draw one or more planar images and then fade them in or out for visual effect. An image frame buffer is subdivided to store multiple images provided by the user, and the resulting multiple images are combined as a single image within a display window on a pixel by pixel basis by the invention. The invention sums the pixel color data on a per-pixel basis, and the pixel data is scaled as a separate operation using color map entries. This permits image fading, which is used in conjunction with the image blending to provide real-time fading of one image into another or is used alone to simply fade one image on a per-pixel basis. The fading may be done by scaling all of the entries from a color map by some value, and this can be done without redrawing the image. The invention also allows for separate processing of data within each window by defining each pixel with respect to its window boundaries.