JVET-Q0330 On block partitioning at picture boundary [R.-L. Liao, J. Chen, Y. Ye, J. Luo (Alibaba), S.-T. Hsiang, C.-Y. Lai, C.-Y. Chen, Y.-W. Huang, S.-M. Lei (MediaTek)]
In VVC draft 7, a block that exceed the picture boundary is forced to be split until all the samples are located inside the picture boundary. However, none of splitting methods is allowed to split the block in the following two cases:
- A CTU block exceeds picture boundary and both the CTU size and min QT size are set to 128;
- A block exceeds picture boundary and its size is not larger than min QT size, and min QT size is larger than the min CU size and the max BT/TT depth is equal to 0.
In this contribution, it is proposed to use QT splitting in these two conditions.
Both are cornercases not exercised in CTC which would typically not be used, but there is obviously a bug in the spec. Another option could be to impose a bitstream constraint saying that if these settings are used, the picture size should be a multiple of CTU size. This would however be too much of a constraint, and it is not clear if the two cases above are the only cornercases that might exist.
Decision (BF/text&SW): Adopt JVET-Q0330 bug fix in implicit split at boundary.