PARTIAL CLOSED-LOOP VERSUS OPEN-LOOP MOTION ESTIMATION FOR HDTV COMPRESSION

Motion estimation is a vital function of video coders that use motion compensated prediction to exploit the temporal redundancy of video signals. The reference images used in the motion estimation process can be either original images (open-loop architecture) or reconstructed images (closed-loop architecture). While the closed-loop architecture is intuitively superior to the open-loop architecture, closed-loop motion estimation is more difficult to implement in a real-time video encoder. A compromise is to perform open-loop integer-pel accurate motion estimation followed by closed-loop half-pel accurate estimation. In this article we present a comparative study of the performance of half-pel closed-loop versus open-loop motion estimation for coding of high definition television with the MPEG algorithm. Simulation results indicate that on average, closed-loop half-pet accurate motion estimation provides slightly better performance than open-loop half-pel accurate estimation. This improvement depends on the bit rate of the coded video bitstream. For relatively high bit rates, the closed-loop implementation often provides no improvement, and sometimes an actual degradation of performance. An analysis of why a closed-loop implementation does not guarantee a better performance is presented. (C) 1995 John Wiley and Sons, Inc.