JVET-P0150 CE3-related: Simplification of reference luma intra prediction mode derivation [Z.-Y. Lin, T.-D. Chuang, C.-Y. Chen, C.-W. Hsu, Y.-W. Huang, S.-M. Lei (MediaTek)]
In VVC Draft 6, the special settings for the reference luma intra prediction modes are not unified, and many checks are required to set the reference luma intra prediction mode. In this contribution, simplified reference luma intra prediction mode derivation is proposed. In the beginning of each coding tree unit (CTU), stored luma intra prediction modes of luma blocks are initialized to DC. If a luma block is coded with combined inter and intra prediction (CIIP), intra prediction without matrix-based intra prediction (MIP), or block-wise differential pulse code modulation (BDPCM), its stored luma intra prediction mode is updated to planar, the luma intra prediction mode of the luma block, and vertical/horizontal according to the BDPCM index, respectively. In the reference luma intra prediction mode derivation, if the reference luma block is available, its stored luma intra prediction mode is used, and only block availability checks are required. It is reported that the proposed method results in 0.00%/-0.08%/-0.07%, 0.00%/-0.10%/-0.13% and -0.03%/0.04%/0.14% Y/Cb/Cr BD-rates with negligible runtime changes for VTM6.0-AI, VTM6.0-RA and VTM6.0-LB, respectively.
It was commented that there is no problem with the design, which was discussed during last meeting. It is claimed that the benefit of the proposal is that conditions are reduced, for example, in dual tree the DM chroma mode does not need to check MIP, IBC, palette, … The proposal initializes modes as DC. It was commented that for MIP the number of conditions is the same (for luma it seems to be editorial change, while for chroma there is no harm). For CIIP, the mode is initialized as planar.
Editor comments that it adds work, but that only a few lines are removed. However, it is claimed by the proponent that condition is saved. Overall, the benefit is considered very minor for the change.
The BoG recommended no action.