International organisation for standardisation organisation internationale de normalisation

CE4: Residual prediction (21)

(Chaired by A. Vetro)

1. Summary (1)

14.1.1.1.1.1.1.1.28JCT3V-G0024 CE4 Summary Report: Residual Prediction [L. Zhang, J.-L. Lin]

Complexity Reduction

JCT3V-G0158: it is claimed to simplify the inter-view ARP by utilizing the following aspects:

• 
  The temporal motion information used in inter-view ARP is derived using the same way as shifted temporal inter-view merging candidate derivation process. This would be a unification of the MV derivation process with the existing MV candidate derivation process. It was stated that complexity increases since there would be an increase in checking of the reference picture list. Editorial improvements to the test were encouraged.
  
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  The residual and residual predictor are calculated as temporal residuals from current view, and the reference view, respectively. It was asserted that two branches in the ARP process could be unified into a single branch, but there is some difference of opinion on this. There is also some minor loss with this proposal.
  
• 
  The disparity vector from DoNBDV process is updated to the coded disparity motion vector associated with current block. Not relevant since DoNBDV is not used in ARP. This aims to improve coding efficiency and could be considered separately.
  
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  Removal of the constraint of DV-MCP: It is proposed that in NBDV derivation process, the DV-MCP information of spatial neighbouring blocks are always checked even they are not coded as skip mode. Further study of this aspect without DoNBDV, but not needed to study as part of CE.
  
• 
  Combination of inter-view and temporal ARP: The DVs from NBDV and DoNBDV processes are both updated to the disparity motion vector associated with current block, if available. The updated disparity vectors are used in ARP process. It is not clear that this is a simplification since the current ARP does not use DoNBDV.
  

No action on any of the above aspects.
JCT3V-G0033: This contribution proposes to disable ARP for 4x4 chroma blocks. Simulation results show that the proposed method introduces 0.1% coding loss for non-base texture views and minor coding loss for coded texture views (0.03%).

Complexity analysis shows that worst case bandwidth for ARP is 22% higher that HEVC v1 with 8x8 bi-prediction case. By disabling ARP for 4x4 chroma blocks, the worst case is then defined by 16x16 ARP; there is only a 5% relative increase in memory bandwidth for this. It was asserted by the proponent that this is a more appropriate trade-off between complexity and coding efficiency.

A detailed analysis is provided in the contribution and was reviewed. It was mentioned that there is some mismatch with earlier analysis (22% in the contribution versus 15% in an earlier analysis). The difference may be due to differences in memory access pattern assumptions. The proposed simplification was agreed, but some offline discussions will be done to clarify.

Further study in CE (together with G0121).