Optimized Adaptive Loop Filter Based on the Refined Adaptation Parameter Sets in H.266/VVC

Adaptive loop filter (ALF), including luma ALF, chroma ALF, and cross-component adaptive loop filter (CCALF), has been adopted in H.266/versatile video coding (VVC). It can enhance the quality of reconstructed videos based on the Wiener filtering principle. In-depth analyses reveal that the efficiency of chroma ALF and CCALF is significantly lower than that of luma ALF, primarily due to the insufficient number of chroma-related filter sets in the adaptation parameter sets (APSs). To address this limitation, this paper focuses on the efficient design of ALF APSs. Specifically, we propose a luma-guided rate-distortion optimization (RDO) criterion for chroma components to improve the efficiency of the new ALF APS. Furthermore, an improved ALF APS list management is introduced to extend the lifetime of chroma-related filter sets in the ALF APS list.