Patent ID: 7693337

Claim:
A method of compressing an image block comprising multiple image elements, said method comprising the steps of: a computer-implemented color quantizer determining a color codeword that is a representation of the colors of said multiple image elements; a computer-implemented alpha quantizer providing an alpha codeword comprising multiple quantized alpha values that are representations of at least one alpha value of said multiple image elements; a computer-implemented intensity quantizer providing an intensity codeword that is a representation of a set of multiple intensity modifiers for modifying the intensity of said multiple image elements; a computer-implemented sequence provider providing an index sequence of image element associated indices; and a computer-implemented mode selector selecting a compression mode based on said alpha codeword, wherein if said selected compression mode is a first compression mode, said index sequence comprises a first index subsequence that comprises, for each subset of at least one image element in said image block, an intensity index associated with an intensity modifier from said intensity modifier set, and a second index subsequence that comprises, for each image element in at least a portion of said multiple image elements, an alpha index associated with a quantized alpha value from said multiple quantized alpha values, and if said selected compression mode is a second compression mode, said index sequence comprises, for each image element in said image block, an intensity index associated with an intensity modifier from said intensity modifier set.