JVET-L0154 CE3-related: MPM Modifications for Intra Mode Coding [Y.-U. Yoon, D.-H. Park, J.-G. Kim (KAU), J. Lee, J. Kang (ETRI)]

This contribution proposes two modifications of most probable mode (MPM) for intra mode coding. The first is modification of positions deriving MPM candidates and the second is modification of context models for MPM index. First, in the current VTM software, the 3 MPM candidates are derived from neighbours which are adjacent to above-left corner of the current block. In this contribution, the positions deriving MPM candidates are modified to be the same as the positions deriving MERGE candidates. Second, 3 MPMs are signalled by MPM_FLAG and MPM_IDX. The first bin of MPM_IDX is using the bypass coding. In this contribution, the first bin of MPM_IDX is coded by two context models according to predefined condition. This contribution reports the performances on the four tests below:

• Test 1: modified positions deriving MPM candidates
• Test 2: modified context model of MPM_IDX with two context models
• Test 3: modified context model of MPM_IDX with a context model and bypass
• Test 4: Test 2 with Test 1

Under VTM configuration, the experiment results reportedly show 0.07%, 0.08%, 0.10% and 0.15% bitrate savings without increase of the encoding/decoding running time for Test 1, Test 2, Test 3, and Test 4, respectively.

Test 2 and Test 3 have parsing dependency (making coding dependent on neighbour mode conditions)

Test 1 could be a simple and straightforward modification without additional complexity, gives small gain. The same is used in 6 MPM case.

Result for RA were not included. Further study was recommended if the VTM would continue using 3 MPM.