JVET-K0369 CE2-related: Longer Tap Deblocking Filter [A. M. Kotra, B. Wang, S. Esenlik, Z. Zhao, J. Chen (Huawei)]
A new longer tap deblocking filter for the luma component is proposed. The proposed filter mainly targets the filtering of blocking artefacts which arise due to the usage of larger size transform units and coding units. The “longer tap” filter introduces new filter condition checks which consider a wider range of spatial activity along the edges. Furthermore, new longer tap filter coefficients are proposed in order to effectively smooth the edges with blocking artefacts belonging to larger blocks. Our proposal also filters the implicit TU boundaries and allows for parallel deblocking of different CUs.
Moreover, to reduce the line buffer requirements for the “longer tap” filter: For the horizontal edges which overlap with the CTU boundaries, the maximum number of samples used in filter decision and the maximum number of samples used in filter modification from the top block are restricted to be the same as in HEVC deblocking filter. Compared to the deblocking filter used in BMS, the proposed method improves the subjective quality of sequences, especially for the ones which are encoded at lower bit rates. Objective results of the proposed longer tap deblocking filer are as follows:
Over VTM Anchor (AI, RA, LDB): Luma BD-Rate gain of −0.12%, −0.13%, −0.02% is achieved without any increase in EncT and DecT.
Over BMS Anchor (AI, RA, LDB): Luma BD-Rate gain of −0.08%, −0.01%, 0.04% is achieved without any increase in EncT and DecT.
Unlike some other proposals of CE2.2, only one condition is checked to decide for the longer filter. Further, it is claimed that line buffer requirements are reduced. Up to 7 samples are filtered at each side.
It was planned to include this in the next CE.
The CE shall also report about the complexity of the different proposals such as additional line buffer requirements, number of operations due to additional rules, number of operations (worst case) for the filtering, etc.