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An elliptical head tracker

A simple algorithm for tracking a person's head is presented. A two-dimensional model, namely an ellipse, is used to approximate the head's contour. When a new image becomes available, a local search determines the position and size of the best ellipse by maximizing the normalized sum of the image gradient magnitude around the perimeter of the ellipse. The local search begins from a predicted position, using the head's velocity which eliminates the tracker's dependence upon maximum velocity. The tracker operates at 30 Hz and actively controls camera pan and tilt in order to track a person moving in a real environment. The algorithm tolerates full 360-degree rotation of the body as well as moderate amounts of occlusion, and it performs reacquisition of the subject.