Color transformation for the compression of CMYK images

A CMYK image is often viewed as a large amount of device-dependent data ready to be printed. In several circunstances, CMYK data needs to be compressed, but the conversion to and from device-independent spaces is imprecise at best. In this paper, with the goal of compressing CMYK images, color space transformations were studied. In order to have a practical importance we developed a a new transformation to a YYCC color space, which is deviceindependent and image-independent, i.e. a simple linear transformation between device-dependent color spaces. The transformation from CMYK to YYCC was studied extensively in image compression. For that a distortion measure that would account for both device-dependence and spatial visual sensitivity has been developed. It is shown that transformation to YYCC consistently outperforms the transformation to other device-dependent 4D color spaces such as YCbCrK, while being competitive with the image-dependent KLT-based approach. Other interesting conclusions were also drawn from the experiments, among them the fact that color transformations are not always advantageous over independent compression of CMYK color planes and the fact that chrominance subsampling is rarely advantageous.