Perceptual quality metric of color quantization errors on still images

A new metric for the assessment of color image coding quality is presented in this paper. Two models of chromatic and achromatic error visibility have been investigated, incorporating many aspects of human vision and color perception. The achromatic model accounts for both retinal and cortical phenomena such as visual sensitivity to spatial contrast and orientation. The chromatic metric is based on a multi-channel model of human color vision that is parameterized for video coding applications using psychophysical experiments, assuming that perception of color quantization errors can be assimilated to perception of supra-threshold local color-differences. The final metric is a merging of the chromatic model and the achromatic model which accounts for phenomenon as masking. The metric is tested on 6 real images at 5 quality levels using subjective assessments. The high correlation between objective and subjective scores shows that the described metric accurately rates the rendition of important features of the image such as color contours and textures.