JVET-P0335 AHG15: Chroma QP mapping table for HDR [T. Lu, F. Pu, P. Yin, S. McCarthy, W. Husak, T. Chen (Dolby)]
This contribution proposes to update the non-normative chroma QP mapping tables for HDR to improve the luma and chroma balance in VTM 6.0 for HDR common test conditions (CTC). It is proposed that:
- For class H1 (PQ content), use separate tables for Cb/Cr and joint CbCr. The tables are derived by absorbing the WCGPPSoffsets for P3 content into the mapping. More than 30% BDrate gain in wPSNRY can be achieved compared with HM16.18 anchor. Subjective evaluation has been performed on PQ reference display (Pulsar) and it is verified chroma coding performance is similar to the current VTM 6.0 anchor.
- For class H2 (HLG content), two candidate tables are provided for selection.
It is agreed that the current CTC setting of the mapping table is not appropriate.
It is asked how “absorbing WCGPPSoffsets” could work as it is currently sequence dependent? It is at least removed in the results.
After the viewing session, it was confirmed that the usage of three separate tables for Cb, Cr, and JCbCr provides similar visual quality as the configuration of the VTM6 anchor. Viewing was only performed for PQ content
Decision (CTC): Adopt the aspect from JVET-P0335 to change the chroma QP mapping table for class H1, and change WCGPPSoffsets to 0.
No change for class H2, further study on this aspect was requested.
Informal viewing was performed at EBU. Results and findings are reported in JVET-P1037.