When a blob can find no data to describe (as when a hand or foot is occluded), it is deleted from the person model. When the hand or foot later reappears, a new blob will be created by either the contour process (the normal case) or the color splitting process. This deletion/addition process makes Pfinder very robust to occlusions and strong shadows. When a hand reappears after being occluded or shadowed, normally only a few frames of video will go by before the person model is again accurate and complete.