A Very Low Bit-Rate Video Coding System based on Optical Flow and Region Segmentation Algorithms

Digitalized video and audio system has become the trend of the progress in multimedia, because it provides great performance in quality and feasibility of processing. However, as the huge amount of information is needed while the bandwidth is limitted, data compression plays an important role in the system. Say, for a 176 144 monochromic sequence with 10 frames/sec frame rate, the bandwidth is about 2Mbps. This wastes much channel resource and limits the applications. MPEG (moving picture expert group) standardizes the video codec scheme, and it performs high compression ratio while providing good quality. MPEG-1 is used for the frame size about 352 240 and 30 frames per second, and MPEG-2 provides scalibility and can be applied on scenes with higher de nition, say HDTV (high de nition television). On the other hand, some applications concerns the very low bitrate, such as videophone and video-conferencing. Because the channel bandwidth is much limitted in telephone network, a very high compression ratio must be required. For the channel bandwidth as low as 28.8 Kbps (V.42), full-duplex is necessary, and 4Kbps is reserved for one-way speech, the e ective bandwidth available is only about 10Kbps. As a result, the digital video signal should be compressed 200 times. For conventional codec scheme, such as H.261, the performance is poor when the bit-rate is about 64Kbps. Therefore, MPEG-4 is being developed to satisfy the demand.