HEVC enables deblocking of a prediction unit boundary when the difference in at least one motion vector component between blocks on respective side of the boundary is equal to or larger than a threshold of 1 sample. In VTM, a threshold of a half luma sample is introduced to also enable removal of blocking artifacts originating from boundaries between inter prediction units that have a small difference in motion vectors.
Luma mapping with chroma scaling (LMCS)
In VVC, a coding tool called the luma mapping with chroma scaling (LMCS) is added as a new processing block before the loop filters. LMCS has two main components: 1) in-loop mapping of the luma component based on adaptive piecewise linear models; 2) for the chroma components, luma-dependent chroma residual scaling is applied. Figure 54 shows the LMCS architecture from decoder’s perspective. The light-blue shaded blocks in Figure 54 indicate where the processing is applied in the mapped domain; and these include the inverse quantization, inverse transform, luma intra prediction and adding of the luma prediction together with the luma residual. The unshaded blocks in Figure 54 indicate where the processing is applied in the original (i.e., non-mapped) domain; and these include loop filters such as deblocking, ALF, and SAO, motion compensated prediction, chroma intra prediction, adding of the chroma prediction together with the chroma residual, and storage of decoded pictures as reference pictures. The light-yellow shaded blocks in Figure 54 are the new LMCS functional blocks, including forward and inverse mapping of the luma signal and a luma-dependent chroma scaling process. Like most other tools in VVC, LMCS can be enabled/disabled at the sequence level using an SPS flag.
