JVET-R0230 AHG2: Syntax clean-up for cross component adaptive loop filter [N. Hu, V. Seregin, M. Karczewicz (Qualcomm)]
In VVC draft 8, cross component adaptive loop filter (CC-ALF) is adopted to refine chroma components by using luma samples. Filter coefficients of CC-ALF are signalled in adaptation parameter sets (APSs). In an APS, a Cb (Cr resp.) CC-ALF filter set with up to 4 filters could be signalled and a filter from this Cb (Cr resp.) filter set could be applied to a Cb (Cr resp.) coding tree block. On the other hand, in an APS, a chroma adaptive loop filter (ALF) filter set with up to 8 filters could be signalled and a filter from this chroma filter set could be applied to a chroma coding tree block. In this contribution, CC-ALF filters are unified for the two chroma components. Cb and Cr components share the same CC-ALF filter set in an APS, which is the same method used in a regular chroma ALF. Under common test conditions, compared with VTM-8.0, the average BD rate of the proposed method is
- AI: 0.03%(Y), -0.17%(U), -0.20%(V)
- RA: 0.01%(Y), -0.10%(U), 0.06%(V)
- LDB: -0.04%(Y), -0.16%(U), -0.04%(V)
- LDP: -0.06%(Y), -0.09%(U), 0.21%(V)
The intent of the proposal is unifying CCALF with ALF, using the same APS ID for Cb and Cr at slice.
There is nothing wrong with the current spec, and the proposal might give up some flexibility.
No action was taken on this.