| JCTVC-M0188 Upsampling based on sampling grid information for aligned inter layer prediction [J. Dong, Y. Ye, Y. He (InterDigital)]
This contribution presents an upsampling scheme achieving aligned sampling grids between the EL and the upsampled BL pictures, even when the input BL and EL sequences have non-zero phase shift. The proposed upsampling scheme includes signalling sampling grid offsets between layers in the bitstream and incorporating the signalled offsets into phase filter selection. Simulation results were asserted to show that, when BL and EL sequences have non-zero phase shift, the proposed scheme outperforms SHM-1.0 significantly. In the RefIdx framework, the average {Y, U, V} gains were reported as {−8.8%, −10.4%, −10.5%}, {−6.6%, −4.8%, −4.4%}, {−6.2%, −4.1%, −4.0%}, and {−5.4%, −3.7%, −3.6%} for AI, RA, LDP, and LDB, respectively. Similar performance gain was asserted to apply the IntraBL framework.
It was remarked that sample position derivation had been discussed in Track B, and there had been a BoG set up to work on this (coordinated by J. Chen). It was remarked that there is a problem in the SHM text, and perhaps in the software in this area, and that the SHM text and software do not match.
The contribution proposes to signal relative sampling grid offsets.
It was questioned whether there is a clear need for adjustable luma grid alignment and that this adjustability results in a need for decoders to support more filters since decoders would need to support more phases than would otherwise be necessary for support of limited scaling ratios (e.g. just 2.0 and 1.5 and 1.0). It was remarked that when supporting "extended spatial scalability" (arbitrary resampling ratios), all phases need to be supported anyway. It was suggested to be more apparent that there is an application need for chroma grid alignment adjustability than for luma grid alignment adjustability.
See notes under review of JCTVC-M0465.
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