TERNARY IMAGE TEMPLATES FOR IMPROVED SEMANTIC COMPRESSION

A method and apparatus for carrying out rapid, block-based SAD search operations for facial ellipses in a CIF videophone image frame are disclosed. A set of search templates, each having an ellipse pattern with two concentric, contiguous perimeters is defined and a set of parameter values are calculated off line for each template: a predetermined subfactor, index number, number of pixels in its dithered perimeter pattern, and first and second match thresholds. The pixels in the lower portion of each perimeter in the pattern are thinned by dithering so as to emphasize the upper contour of the ellipse. Values of +2k for interior perimeter pixels and -2k for exterior pixels in the template are then added to corresponding +k edge pixels and -k non-edge pixels in each search position of the template on a thresholded binary edge map of the image frame. The sum is then normalized and the template and search position producing the best SAD match metric value is identified as a facial area, without requiring symmetry detection.