Statistical Dependence Between Components of a Differentially Quantized Color Signal

The statistical dependence (redundancy) between three differentially coded color components of a video-telephone signal are explored by means of an entropy study. We measure the entropy of the differentially coded color baseband signals both jointly and as three separate signals. The source material consisted of a number of portraittype pictures. The color signal is treated in a format containing a baseband luminance channel and two baseband chrominance channels. Various orthogonal and nonorthogonal transformations, including the Karhunen-Loève transform, are applied to the chrominance signals to study the effect on the entropy. With a well-chosen format for the color signal, our results show that the redundancy resulting from using a separate encoding of the signals rather than a joint encoding ranges between 0.2 and 0.5 bits. The possible savings accruing from considering the relationship between coded color differential components was only about 1 percent of the total bit rate for most pictures and increased to a maximum of 4 percent for one particular picture.