US Patent 6956965 Compressing and decompressing an image

Each pixel in an image has its own color value that is defined in a color look-up table. Regions of the image are separated into groups with similar color values. For each group, the color of one of the pixels is selected. The image is compressed by retaining only references to the color look-up table that define the color values of the pixels selected for the groups and a pixel map which indicates for each pixel, the group to which the pixel belongs among the groups which constitute the region. Upon decompression, each pixel is shown with the color of the pixel that was selected for the group to which the pixel belongs.