Lagrangian multiplier optimization using correlations in residues

Rate distortion optimization (RDO) algorithm plays the vital role in the up to date hybrid video codec H.264/AVC. The RDO algorithm of H.264/AVC reference software is built up by assuming that the transformed residues are memoryless variables. However, our experiments reveal that, for some sequences, the strong temporal correlations exist in the prediction residues. This paper extends the Lagrangian optimization techniques by modeling the transformed residues as the first-order Markov source and calibrating the distortion model with the piecewise approximation function. The proposed algorithms adjust the Lagrangian multiplier dynamically to improve the overall coding quality. Comprehensive experiments testify that, as compared with the JM reference software, our optimizations can achieve up to 1.875dB coding gain. Moreover, our algorithms posses more robust coding performance and introduce less computational overhead than the Laplace distribution based methods. The inherent short process latency makes it possible to cooperate our algorithms with rate control operation. Last but not least, the proposed approach is also useful for the emerging standard, HEVC.