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SCC parallel processing (AHG14) (8)
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SCC parallel processing (AHG14) (8)13.0.0.1.1.1.1.1.311JCTVC-S0070 AHG14: On IBC constraint for Wavefront Parallel Processing [G. Laroche, T. Poirier, C. Gisquet, P. Onno (Canon)] (Consideration of this topic was chaired by G. Sullivan on Saturday 10-18 p.m.) This contribution is related to the IBC and WPP. It is proposed to constrain the IBC referencing range for WPP to avoid having the IBC predictor refer to a non-reconstructed block. The constraint rule consists in limiting the IBC search range to the potential reconstructed blocks when WPP is enabled. The proposed rule results in average BDR losses of 0.6%, 0.3%, 0.1% for AI, RA and LDB configurations, respectively, compared to SCM2.0 when WPP is enabled. The proposal is to limit IBC references to preceding CTUs in wavefront order. There is some coding efficiency penalty. The peak per-category loss is 1.4%. It was discussed whether to impose the constraint always or only when ECS is enabled. It was noted that even if the bitstream is not wavefront-structured, the post-parsing decoding process can be wavefront structured if this constraint is imposed. The area constraint proposed in this contribution is somewhat less restricted than in some related contributions. Decision (BF): Adopt the constraint, regardless of whether wavefront is being used. A CTU can reference one CTU to its right in the previous row, but not further to the right than this. Further discussion was chaired by J. Boyce: Decision: In subsequent discussion, a further restriction proposed in S0088 was adopted. 13.0.0.1.1.1.1.1.312JCTVC-S0231 AHG14: Cross-check of JCTVC-S0070 on IBC constraint for Wavefront Parallel Processing [P. Lai, X. Xu (MediaTek)] [late] The cross-check had not yet been completed when the initial discussion occurred. It was later uploaded, and confirmed the results. 13.0.0.1.1.1.1.1.313JCTVC-S0088 On WPP with palette mode and intra BC mode [B. Li, J. Xu (Microsoft)] (Consideration of this topic was chaired by J. Boyce on Saturday 10-18 p.m.) This document discusses the interaction between WPP and palette mode and Intra BC mode.
The contribution proposes to align palette prediction the existing CABAC design when WPP is used. The current design requires storage of the palette for a single LCU, and the proposal would require storage of the entire LCU row's worth of palette. Storage requirement is 287 bytes per LCU row if raster scan decoding is used. If WPP decoding is used, the storage requirement is N*194, with N threads. A participant asked whether the previous palette or the palette predictor is proposed to be stored and used for the proposal. It is the palette predictor. JCTVC-S0141 is related. The coding gain when palette and WPP are used is in the range of 0.0–0.7% for lossy and 0.0–0.5% for lossless. A second aspect of this contribution proposes to restrict which above CTUs are available for use for IBC, and is similar to JCTVC-S0070, but is more restrictive as to which CTUs can be used. For the less restrictive proposal in S0070, additional checks are required by the decoder to determine whether decoding can be done than with this proposal. No experimental data was provided in the contribution, but may be available in JCTVC-S0200. Decision: Adopt the IBC constraint region proposed here, where one addition CTU to the right of the current CTU may be used in each row above, at a 45 degree angle. The constraint will apply regardless of whether or not WPP is used in the bitstream. This aspect of applying regardless of whether WPP used was proposed in S0220. The palette aspect was further discussed 10-23 p.m., chaired by J. Boyce. JCTVC-S0141 also proposed to align palette prediction with CABAC when WPP is used. Decision: Adopt the palette prediction alignment with CABAC when WPP is used, also proposed in S0141. 13.0.0.1.1.1.1.1.314JCTVC-S0242 Cross-check of S0088 (On WPP with palette mode and intra BC mode) [W. Wang, M. Xu, Z. Ma, H. Yu (Huawei USA R&D)] [late]
(Consideration of this topic was chaired by J. Boyce on Saturday 10-18 p.m.) This contribution presents modifications to the IBC reference area, such that when WPP is utilized in the bitstream, IBC can only reference blocks within the already reconstructed CTUs by the WPP threads. With WPP turned on (WaveFrontSynchro > 0 in configuration files), two reference area patterns are tested:
Related to JCTVC-S0070 and S0088. This proposal is even more restrictive, and has more loss, up to 2.9%. See notes on S0070, S0088, and S0220. 13.0.0.1.1.1.1.1.316JCTVC-S0274 AHG14: Cross check of JCTVC-S0101 on Intra Block Copy reference area for Wavefront Parallel Processing [P. Onno (Canon)] [late] 13.0.0.1.1.1.1.1.317JCTVC-S0141 Using the wavefront store-and-sync design for palette table prediction variables [K. Misra, S. H. Kim, A. Segall (Sharp)] [late] This is the same as part of S0088. See S0088. 13.0.0.1.1.1.1.1.318JCTVC-S0257 Cross-check of using the wavefront store-and-sync design for palette table prediction variables (JCTVC-S0141) [V. Seregin (Qualcomm)] [late] 13.0.0.1.1.1.1.1.319JCTVC-S0220 On parallel processing capability of intra block copy [K. Rapaka, V. Seregin, C. Pang, M. Karczewicz (Qualcomm)] [late] Chaired by J. Boyce, Sat. This contribution proposes methods to enhance parallel processing capability when intra block copy (IBC) mode is enabled. IBC mode uses previously decoded unfiltered samples within the same picture for its prediction. This introduces a dependency that prediction samples of the current block have to be reconstructed before processing the current block. In this contribution some restrictions and indications are proposed on IBC block vectors (BV) to allow decoder to be able to parallel process multiple CTUs in non-raster scan order. In the revision 1 of the document, simulation results were provided for different delay restrictions proposed for intra BC. Related to S0070, S0088, and S0101. This proposal proposes applying the IBC constraint regardless of whether WPP is used in the bitstream. The contribution proposes, in "Option b", signalling in the slice header of what type of restriction is imposed. This could also be signaled in the PPS, SPS or VUI. It was questioned whether signalling is more appropriate than a normative restriction. Three different constraint patterns were proposed, with experimental data provided for each. The experimental data does not use WPP in the bitstream encoding. Decision: Adopt the figure 4.1 pattern of IBC constraint, as is also noted under JCTVC-S0088. 13.0.0.1.1.1.1.1.320JCTVC-S0306 Cross-verification of JCTVC-S0220 On parallel processing capability of intra block copy [X. Xiu (InterDigital)] [late] (Has "the" problem in abstract phrasing.)
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