JVET-R0353 AHG14: On Interaction between ACT and BDPCM [T. Tsukuba, M. Ikeda, Y. Yagasaki, T. Suzuki (Sony)]
In HEVC, RDPCM, which is a similar coding tool to BDPCM in VVC, can be applied to both luma and chroma components when Adaptive color transform is used. On the other hand, in current VVC, interaction between ACT and Intra BDPCM is inconsistency; When ACT is used, Intra BDPCM for chroma is normatively disallowed while Intra BDPCM for luma is allowed.
This contribution proposes to enable a combination of ACT and Chroma BDPCM, which makes the interaction between ACT and Luma/Chroma BDPCM consistency.
Simulation results show that:
For 4:4:4/lossless condition (DualTreeOn),
- Average bitrate differences for RGB are 0.0% for AI, -0.71% for RA and -0.90% for LB
- Runtimes (Enc, Dec) for RGB are (99%, 97%) for AI, (100%, 97%) for RA and (101%, 98%) for LB
For 4:4:4/lossless condition (DualTreeOff),
- Average bitrate differences for RGB are -2.19% for AI, -1.23% for RA and -1.19% for LB
- Runtimes (Enc, Dec) for RGB are (96%, 92%) for AI, (99%, 98%) for RA and (100%, 96%) for LB
For 4:4:4/SCC/common QP condition (QP=22, 27, 32, 37, DualTreeOff),
- Average BD-rate differences (R, G, B) are (0.07%, 0.10%, 0.09%) for AI, (0.01%, 0.03%, 0.04%) for RA and (-0.07%, -0.06%, -0.07%) for LB
- Runtimes (Enc, Dec) for RGB are (96%, 97%) for AI, (99%, 100%) for RA and (99%, 97%) for LB
For 4:4:4/SCC/low QP condition (QP=2, 7, 12, 17, DualTreeOff),
- Average BD-rate differences (R, G, B) are (-0.22%, -0.18%, -0.20%) for AI, (-0.05%, -0.08%, -0.13%) for RA and (-0.13%, -0.14%, -0.17%) for LB
- Runtimes (Enc, Dec) for RGB are (95%, 99%) for AI, (99%, 100%) for RA and (99%, 98%) for LB
It is reported that, to reduce encoder run time, BDPCM flag for luma was always set to the same value as luma.
Similar proposals were made by the last meeting, and these were not adopted, as it was assessed that the compression benefit was too low (was in a similar range as with the new contribution).
It is not really an obligation to keep the same design as HEVC – VVC is a different standard, and what was good in HEVC may not be relevant here.
No action was taken on this.