JVET-P0511 Non-CE3: ISP extension to avoid small Chroma intra blocks [L. Zhao, X. Li, X. Zhao, S. Liu (Tencent)]
In VVC Draft 6, Small Chroma Intra Prediction Unit (SCIPU) has been adopted, which avoids 2x2, 2x4, and 4x2 small chroma intra blocks in single tree. However, it creates a local dual tree in single tree. It is reported that it needed a lot of software and spec text changes. In this contribution, an alternative method to avoid small chroma intra blocks is proposed, which needs less software and spec text changes. It includes two steps. In the first step, 4x4, 4x8, and 8x4 intra CU is disallowed in single tree so that 2x2, 2x4, and 4x2 chroma intra CBs is avoided. In the second step, ISP is extended to support binary tree split (BT) for 8x8, 4x16, and 16x4 CUs, and one flag is added to indicate whether current luma CU is split into 2 partitions or 4 partitions. Same as ISP in VTM-6, the extended ISP is only applied to luma component. It is reported that the proposed method achieves 0.01% and 0.09% luma BD-rate changes for AI and RA configurations, respectively.
It was commented that it seems more related to the partitioning topic and the proposal may be relocated to that section.
It is further commented that the RA loss of 0.09% is significant. The proposal introduces the PU concept and extends ISP to support BT for 8x8, 4x16, 16x4, etc.
It was commented that last meeting the SCIPU concept was adopted and the proposal would replace the concept. The measured loss seems due to less flexibility in the proposed method. Coding performance of single tree is missing and it was commented that given the RA loss that the AI single tree loss will be significant.
An editor comments that SCIPU was integrated and bug fixed and that, while it would have been nice to have more alternatives last meeting, that it is too much of a burden to change the design.
The BoG recommended no action.