Cross-component Sample Adaptive Offset

This paper proposes one new In-loop filtering technique cross-component sample adaptive offset (CCSAO) for further coding efficiency improvement beyond Versatile Video Coding (VVC). The CCSAO reduces the sample distortion by 1) utilizing the strong correlation between luma and chroma components to classify the reconstructed samples into different categories and 2) deriving one offset for each category and adding the offset to the samples in the category. The offset of each category is properly derived at encoder and signaled to decoder. To keep the design at low complexity, only band information of reconstructed samples is considered for the sample classification of the CCSAO. To verify the performance, the proposed CCSAO is implemented on top of the enhanced compression model (ECM) for the joint video exploration team (JVET)'s exploratory work of future video coding technologies beyond VVC. Simulation results show that the CCSAO achieves average {0.20%, 2.83%, 2.98%} and {0.41%, 7.36%, 7.36%} Bjentegaard delta (BD)-rate savings for {Y, U, V} components under the Random Access and Low Delay B configuration, with negligible complexity impacts on encoding and decoding complexity. The proposed CCSAO scheme has been adopted to the ECM-2.0 software platform.