JCTVC-M0437 Cross-check of coefficient level cRiceParam updates for screen content coding (JCTVC-M0316) by TI [S. H. Kim, A. Segall (Sharp)] [late] [miss]
JCTVC-M0366 AhG8: Simplified update of the coefficient level Rice parameter [J. Sole, M. Karczewicz (Qualcomm)] [late]
Related to M0316, and is suggested to be simpler than that contribution.
This contribution presents a modified update process of the Rice parameter of the syntax coeff_abs_level_remaining to reportedly improve HEVC RExt lossless and visually lossless coding efficiency for screen content coding. The proposed modification removes one condition check while reportedly improving bit rate savings under RCE2 lossless and range extensions common conditions. For the lossy case, results are also provided when the proposed update is only applied to transform skip.
Gain was reported on all content (for lossless coding), although the gain was negligible for non-screen content. At low QP values it also provides a gain for lossy coding for screen content, although it had some losses for non-screen content.
The contributor also suggested that the scheme could only be applied in the transform skip case. (However, it might be better for an implementer to just switch using an SPS-level decision rather than on a block-by-block basis.)
Gain for SC (RGB) lossless sequences is reported as 4.3%/3.5%/3.4% for AI/RA/LB (for the max Rice parameter equal to 4).
It was commented that we should make sure not to test too much with RGB, and be careful about adopting things that might not provide gain with YCC domain coding.
Further study in a CE was planned.
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