Patent US 4,887,151

There is disclosed an apparatus for efficient and faithful encoding of color image data, by dividing color image data into blocks, extracting luminosity information, structure information and color information from each block, and for each block, individually encoding or individually quantizing the color image the structure information and the luminosity information. The signal system may be one employing signals of low mutual correlation, such as an L*a*b* signal system. An orthogonal transformation of the L* components of the color image data for the respective blocks may be performed.