Abstract: A method for increasing the speed of a Z-buffer process. The method operates on the observation that groups of points in a scan-line of a polygon are either all visible or all obscured by existing points in the frame buffer. The method processes visible points separately from obscured points. The method only calculates changes in point intensity for the groups of visible points. In addition, the termination of the two separate processes is controlled by placing sentinels at the edge of each scan-line of the polygon so that the comparison of the point's z-values also act as a check for process termination.