Subband coding of color images with limited palette size

An approach for compression of color images using a sorted color palette and a subband source coder is presented. When the decoded image is to be displayed on an eight bit monitor this method significantly reduces the decoder computational complexity. To avoid requantization before displaying the decoded image, the encoding and decoding are performed on a pseudo greyscale image which represents the color space defined by a sorted palette. To sort the palette, a measure for color similarity is needed. Here an l₂ distance in the RGB and luminance-chrominance color space has been studied, and a new color correlation measure is proposed. For comparison a transform source coder (JPEG) is used to encode the pseudo greyscale image. Simulation results show that the subband source coder gives better results than the transform source coder. The quality of the decoded color images is surprisingly good