Apparatus for determining motion vectors

An apparatus, for use in a motion-compensated video signal encoder, for determining motion vectors representing a displacement between a current frame and a reference frame of video signals, wherein the current frame is divided into a plurality of processing blocks, each processing block having P.times.Q pixels with P and Q being integers larger than two and said P.times.Q pixels include therein an object pixel, the object pixel representing a pixel located at the center of each processing block, which comprises:

• means for providing a motion vector for each of the pixels included in the current frame, the motion vectors including object motion vectors, each of the object motion vectors being a motion vector for each of the object pixels;
• median filter for filtering the motion vectors to generate filtered motion vectors for the pixels included in the current frame, said median filter having a cross-shaped filtering window for averaging the motion vectors therein;
• means for counting a number of filtered motion vectors having a same value among the filtered motion vectors corresponding to the pixels included in each processing block, thereby sorting out first and second major vectors, the first and the second major vectors representing the filtered motion vectors having the largest and the second largest counted numbers, respectively, for said each processing block;
• means for calculating error functions for said each processing block based on the first and second major vectors to thereby select as an output motion vector one of the first and second major vectors which yields a smaller error function;
• means for generating a control signal based on the object motion vector, the first major vector and the counted number of the first major vector for said each processing block;
• and
• switching means, responsive to the control signal, for selecting one of the output motion vector and the object motion vector as the motion vector for said each processing block.