Joint Collaborative Team on Video Coding (jct-vc) Contribution
Non-CE Technical Contributions 6.1Range extensions
Yüklə 1,46 Mb.
|
6Non-CE Technical Contributions6.1Range extensions6.1.1GeneralSee also M0094 (on requirements / profiles). JCTVC-M0178 AHG5: Range Extensions and High Bit Depths [K. Sharman, N. Saunders, J. Gamei (Sony)] (Initially reviewed in BoG M0462 Wed. p.m. chaired by D. Flynn.) The contribution contained a thorough study of various aspects. Extended precision of internal processing elements was suggested in the contribution. It was noted that using a fixed precision expansion width would seem preferable (e.g. based on profile/level). Some bit depth expansion phenomena were reported and a modification of the entropy coding was proposed to handle this (with dependencies on QP). Benefit from sign data hiding was reported to be negligible. Throughput was analyzed and a modification of bypass bin handling was proposed to establish alignment with the bits coded in the bitstream. Some benefits were reported for 14 bits as well as higher precision. Profiling was discussed in the contribution, but this aspect was not discussed in detail by the group as there was other input on that and further study was understood to be needed about this. Notes from BoG report to be integrated. Further study in AHG was requested. JCTVC-M0256 Suggested fixes for HEVC Range Extensions draft text [D. Flynn, J. Sole, T. Suzuki] [miss] It was suggested that this contribution did not need to be presented in detail, as the proposed editorial improvement had been superseded by other decisions. JCTVC-M0298 Bandwidth reduction for range extension [V. Seregin, X. Wang, J. Sole, M. Karczewicz (Qualcomm)] (Initial discussion chaired by D. Flynn.) HEVC Range Extensions 4:4:4 potential applications include consumer applications, so the complexity increase due to the 4:4:4 processing has to be taken into account. The scope of this contribution is the bandwidth of 4:4:4 motion estimation and compensation, which is around 37% greater than the 4:2:0 case for 4×2 memory block. Specifically, in this contribution, restriction of bi-directional prediction for 8×8 chroma components is studied, while luma component still can have bi-prediction. This modification reportedly increases bandwidth by 9%, as opposed to 37%, relative to 4:2:0. The impact on coding performance is reportedly about 0.2% and 0.4% luma BD rate loss for Main-tier RA and LB, and High-tier RA and LB respectively in for both YUV422 and YUV444. The impact on chroma was reportedly about 0.3–1.1%, depending on the test case. The contribution proposes two methods, the first restricts 8x8 Bi-pred for all components, including luma, and the second proposes to implement the restriction just for motion compensation of the chroma components. It is suggested that this only is applied to 4:2:2 and 4:4:4 chroma formats. It was suggested that there could conceivably be two 4:4:4 profiles, one targeting consumer applications and the other at higher operating points. Should this then depend upon the profile? Yes, as in some cases or application areas it may not be an issue. Support was expressed for the proposal, remarking that there are application areas which would benefit from this. Adoption of the second method (8x8 Bi-pred restriction for chroma) was initially recommended. In further discussion, a participant remarked that the introduction of differences between the handling of luma and chroma in the 4:4:4 case is undesirable. However, other differences were noted to exist – in regard to:
The modification was noted to cause a conversion from a bipred prediction applied to luma to a mono-prediction applied to chroma, as the chroma MVs are derived from the luma MVs. The loss from completely disabling bipred for 8x8 was substantially larger. It was asked whether the test sequences include any fading sequences, which are likely to benefit from biprediction. Further study was encouraged. It is acknowledged that memory bandwidth is a major concern and should be analyzed. JCTVC-M0345 Cross-check for bandwidth reduction for range extension [E. Alshina, S. Lee, J. Min] [late] JCTVC-M0335 AhG5: Offset Scaling in SAO for High Bit-depth Video Coding [W.-S. Kim, J. Sole, M. Karczewicz (Qualcomm)] (Initially reviewed in BoG M0462 Wed. p.m. chaired by C. Rosewarne.) Notes from BoG report to be integrated. The bit depth of the SAO offset value was studied and two possible modifications were proposed. Related to M0118. The BoG recommended adoption of the first (simpler) modification and further study. The gain for IBDI for 8 bit content coding, relative to using 8 bit coding, had previously been observed to decrease as coding bit depth increased beyond 10 bits when not applying the modification. With the modification, the gain became roughly constant beyond 10 bits, which is the same behaviour observed with SAO disabled. Thus the proposed scheme was characterized as a fix to undesirable behaviour.
(Initially reviewed in BoG M0462 Wed. p.m. chaired by D. Flynn.) Notes from BoG report to be integrated. The bit depth and unary coding of the SAO offset value were studied. Related to M0335. Further study was recommended. JCTVC-M0344 Cross-check for Removal of the offset quantization in SAO [S. Jeong, J. Min, E. Alshina] [late] Yüklə 1,46 Mb. Dostları ilə paylaş:
|