H.324系统中,H.263图象编码速度一直是影响系统实时性能的瓶颈,而运动搜索和DCT等模块又是其中运算量最大的模块.为了进一步降低图象编码的运算量,提出了一种基于零块发现的运动搜索方法.该方法在对活动图象进行运动搜索时,应用了一种基于发现全零块的中止准则,使得H.263中占用运行时间最多的INTER块的运动搜索,收敛得更快,它尤其提高了对背景图象或者变化较小的图象部分的编码效率,同时也较大幅度地减小了DCT等模块所占用的计算时间.该算法在提高速度的同时,仍保持了H.263原有压缩算法的效率和图

To further improve the performance of H.263' s encoder in the real time H.324 system, a motion search algorithm using zero block detection technology, is proposed in this paper. This algorithm exploits the fact that many residual blocks become all zero blocks after DCT and coarse quantization in very low bit rate video coding. To further speed up the encoder implementation, this zero detection technology is combined with motion estimation. In the motion search process, if an all zero macro-block is detected using the distortion value of the macro-block, the search process is stopped. The choice of the threshold for zero detection is critical. Simulation results show that the algorithm can dramatically decrease the motion search points. And also many blocks' quantization, DCT and other reconstruction steps are skipped. Under typical quantization parameter of 12, the average search points decrease is 30%~50%, and 25%~30% blocks' DCT and quantization is skipped due to the zero detection in the motion search. With the gain of encoder speed, the algorithm does not suffer the coding efficiency of the H.263 baseline. The algorithm does not affect the reconstructed image quality either. After the algorithm is combined into a real~time H.324 system, the performance of the whole system is improved a lot.