I am using a format of the bitmap which is based on the palette of N colors:
Color[] Palette = {
color1, color2, color3, ..., colorN
};
The bitmaps itself is represented as an array of indexes to the colors from this palette. A Width and Height are specified.
The problem is:
For any fixed N and any standard bitmap determine the best palette.
Yay for Google.
http://www.adrianhopgood.com/pub/IEEE-SMC2006.pdf
http://itee.uq.edu.au/~aprs/dicta2003/pdf/0781.pdf
http://www.leptonica.com/papers/colorquant.pdf