Patent US 5,699,129

Video compression systems often use motion compensation to compress the data. Motion compensation systems usually use motion vectors to represent motion. A multipass motion vector determination unit is introduced that makes more then one pass to select a motion vector. The multipass motion vector determination unit first examines an initial search window area around each macroblock to select a first motion vector for each macroblock. The multipass motion vector determination unit then determines a second search window for each macroblock based upon the first motion vector found for that macroblock. Specifically, the second search window consist of an area located in the direction of the first motion vector. A second motion vector is selected from the second search window. Additional motion vectors may similarly be selected. Finally, the multipass motion vector determination unit then selects a final motion vector from the motion vector collected by finding the motion vector having the smallest summation of absolute difference value.