VIDEO IMAGE COLOR ENCODING

A method is described of encoding pixel color values for a digital video image frame in which each different color within the image is assigned a color value. A predominant color is identified for the image frame and, in a first embodiment (FIG. 5), each pixel having a color other than the predominant color is separately coded as its respective color value (0010 to 1111), with runs of three or more successive pixels of the predominant color being run-length encoded. A further code (0000 0011 cccc), similar in arrangement to that indicating a run, is provided to allow a change in the specified predominant color during the course of a frame. In a further embodiment, runs of all colors are run-length encoded but with a shorter coding scheme for runs of the predominant color or, in a still further embodiment, a small range of predominant colors. A principle use for these coding schemes is to improve efficiency of coding for certain classes of image material.