Abstract: A technique for encoding pixel color values for a full or partial digital video image frame has each different color within the image being assigned a color value. The most common one of the colors (0) within the frame or frame segment is identified, and runs of at least three successive pixels of that predominant color are encoded as a first code (00) indicating a run and a second code indicating the run length (LL). Runs of successive pixels having a color (1, 2, 3) other than the predominant color (0) are encoded as successive iterations of a code containing only the respective color value when the run length is less than or equal to a threshold value and as a first code indicating a run (00), a second code indicating a run length (LL), and a third code (CC) identifying the color value when the threshold value is exceeded.

Abstract: In an image processing system for providing two-dimensional pixel images comprised of a purality of polygonal image primitives and a background, the polygonal image primitives representing a three-dimensional object, a Z buffer and a color buffer are cleared by the steps of rendering image primitives relating to foreground in the color buffer (354) and the Z buffer (353); and subsequently scanning the Z buffer and for each pixel, if the Z value is a predetermined background value such as zero (357), clearing the corresponding location in the color buffer to background color (358), and if the Z value is not the predetermined background value, clearing the Z buffer to that predetermined background value (359). In the method, either a Z buffer or a color value is written during the buffer clearing process, but never both. The pixels may be read from cache in groups, the size of a group being selected to maximize the possibility of all consecutive pixels in a group being either foreground or background pixels.