PERFORMANCE OF THE H.263 VIDEO COMPRESSION STANDARD

The draft international standard ITU-T H.263 is closely related to the well known and widely used ITU-T Recommendation H.261. However, H.263 does provide the same subjective image quality at less than half the bit-rate. In this paper we investigate to what extend single enhanceme nts of H.263 contribute to this performance gain, and consider the tra de-off quality vs. complexity. Based on typical test sequences, H.263 with its various modes is compared to H.261 on the basis of rate disto rtion curves at bit-rates up to 128 kbps. At 64 kbps, the performance gain of H.263 in its default mode compared to H.261 is approximately 2 dB. This improvement is achieved with only little increase of complex ity, and is mainly due to more accurate motion compensation with half- pel accuracy. Considering the trade-off quality vs. complexity, the co mbination of the optional coding-modes ''Advanced prediction mode'' an d ''PB-frames mode'' is a good compromise, resulting in an additional performance gain of 1.5 dB PSNR at 64 kbps. The ''Syntax-based arithme tic coding mode'' on the other hand, offers only a very small performa nce gain (0.1 dB at 64 kbps) for its increased computational complexit y. Results from profiling an H.263 software codec are presented in ord er to support complexity considerations of the optional coding-modes.