CompuServe Messages

HAM is Hold-And-Modify. It works basically by remembering the color of the previous pixel, and changing it. In normal HAM mode, there are 6 bitplanes. The top two bitplanes indicate what the lower 4 bitplanes will be used for. These uses include: Change Red (which changes the red component of the previous pixel to the 4 bit value to get the current pixel), Change Green, Change Blue, and Palette (which looks in a 16 entry palette for the new color, basically the same as a normal 16 color mode). Thus, from any color, you can change to any other color in a maximum of 3 pixels (one each to change Red, Green, and Blue). In practice, one can often change to the needed color in only one or two pixels, and by carefully choosing the 16 colors in the Palette, can further reduce the number of pixels needed to change color to the correct color. BTW, HAM-E has an *8* bit HAM mode which basically works the same way, only it handles *6* bits for the component data, and can pull from a 64 entry palette instead of only a 16 entry one. –>Steve Bennett