Early detection of all zero chroma blocks in H.263

In very low bit rate video coding, the large quantization parameter makes many blocks all zero blocks. Based on the algorithm using the SAD of the luma to detect the zero luma blocks, this paper proposed an algorithm using the SAD of the luma obtained in motion estimation to predict the SAD of the chroma, which is further used to detect the zero chroma blocks. Experimental results show that the proposed algorithm reduces the computation for the DCT operations including DCT and quantization by up to 64% with negligible image quality degradation. Furthermore, the prediction process is very simple and easy to be implemented in the H.263 encoder