Chroma Coding Efficiency Improvement with Context Adaptive Lagrange Multiplier (CALM)

The increasing interest in higher fidelity video initiated the need of higher efficient coding. Color pictures are usually compressed in a luma-chroma coordinate space. One of the important components in H.264 encoding is to find optimal motion vectors and modes to minimize both luma and chroma coefficients bits. This paper proposes a new simple and efficient method to adjust Lagrange multipliers based on the context (context adaptive Lagrange multiplier or CALM), which improves the accuracy for the detection of true motion vectors as well as the most efficient encoding modes for luma which are used for deriving the motion vectors and modes for chroma. Simulation results show that the chroma bit rates can be reduced by 4.36% and 4.80% for U and V components respectively when compared with that of the JM reference software (version 10.2). In addition, the coding efficiency improvement is comparable to the more complicated rate-distortion optimized (RDO) mode decision techniques.