Dear experts,

there is a possible mismatch in the RExt D5 (01005v4) and HM-12.1+RExt-5.1 for deblocking with 422 subsampling. In the following luma CB/TB partitioning for a 16x16 CB two horizontal edges are considered for filtering:

luma 16x16

| | |
| 8x8 | 8x8 |
| TU | TU |
| | |

| | |
| 8x8 | 8x8 |
| TU | TU |
| | |

For the corresponding chroma part for both 420 and 422 only (1) is considered and (2) is not considered:

TComLoopFilter.cpp:223

{

xEdgeFilterChroma ( pcCU, uiAbsZorderIdx, uiDepth, edgeDir, iEdge );

}

Here there is from my understanding a difference in the text and software exist as the text (8.7.2.5.2) edge (2) also is filtered in 422 but not in 420. It might be a misinterpretation from the text.

The question basically boils down to: do chroma TB and PB boundaries that are in 420 not on a 8x8 grid, and in 422 are promoted to the 8x8 grid, need to be filtered? Note that in the current software chroma CB boundaries that are promoted in such a way are filtered, so for the corresponding case with 4 8x8 CBs would result in both (1) and (2) being filtered for 422.

Best,
Chi