Of itu-t sg16 wp3 and iso/iec jtc1/SC29/WG11

JCTVC-M0314 Cross check JCTVC-M0154 Combination of Merge and GRP [X.  Xiao (??)] (InterDigital)] [late]
JCTVC-M0155 Non-CE3: Enhanced inter layer reference picture for RefIdx based scalability [A. Aminlou, J. Lainema, K. Ugur, M. Hannuksela (Nokia)]

This contribution proposes a method to enable differential coding in RefIdx based scalable coding that does not involve any low level changes, hence argued to be compatible with high-level syntax only scalability. In the proposed method, an additional picture called enhanced inter layer reference (EILR) is added to the enhancement layer decoded picture buffer (DPB). EILR picture is generated by first taking the difference between the enhancement layer reference picture and the upsampled base layer reference picture, based on base layer motion information, and then adding this difference to the current upsampled base layer picture. When using the uncompressed motion information of the base layer, the method improves BD-rate luma on average −2.2%, −3.0 % and −2.7% for RA, LD-P and LD-B test cases, respectively. The improvements are larger for chroma and their average is −6.5%.

Average gain is reportedly around 2.6%. Decoding time increased by around 30-–40% (doubling of motion compensation).

Complexity analysis (average) reports versus refidx approach with picture-level processing, but the implementation of the GRP-like scheme is assuming PU-level processing. In that comparison, 90% memory access is reported, but if it were compared against PU-level refidx, it would be expected that memory accesses are increased.

The proposed approach uses uncompressed motion. More memory and more complex inter-layer processing is necessary for that.

The gain is somewhat lower than in best GRP approaches, likely due to the fact that no weight is used for the residual, and since base-layer motion is used for GRP (similar to base mode).

The overall complexity is not different from GRP approaches. The complexity is shifted here to the inter-layer processing, which still would be a normative part of the decoding process. “High-level only” relates to syntax and semantics.