JCTVC-M0365 Cross-verification of Modified Motion Vector Signalling and Prediction Under Reference Index Based SHVC from Sharp [X. Xiu (InterDigital)] [late]
6.2.9Considerations relating to up-/downsampling filters
JCTVC-M0035 AHG13: Slice based upsampling filter for improved error resiliency [K. Ugur, M. M. Hannuksela (Nokia)]
In spatial scalability, base layer samples are upsampled to enhancement layer resolution and used as reference. If the base layer picture is coded with slices, samples close to the border of the slice are calculated using the samples from another slice. Similar to filtering across slice-boundaries, it is asserted that this increases error propagation and reduces the error resiliency when SHVC is used within error-prone environments. Similar to restricting filtering across slice boundaries, this contribution proposes an optional restriction on upsampling, so that sub-pixel samples never use integer samples from another slice. It is asserted that that the proposed functionality is already present SVC using the constrained_intra_resampling_flag syntax element.
The contribution proposes something somewhat similar to constrained_intra_resampling_flag in SVC.
But proposed as unrelated to intra – using boundary padding when a flag is enabled such that each slice of the base layer is upsampled separately.
The potential for visual artefacts was noted. The contributor had not checked for this, but suggested that it would be less problematic than some other effects, such as disabling of filtering across boundaries.
In any case, encoders should use intelligent selections of when to user inter-layer referencing and when not.
When the proposed flag is enabled, slice boundaries would be treated as picture boundaries for resampling.
For the filtered SNR scalability case, a similar handling would apply.
No simulation results were provided.
It was remarked that the contribution brings up more general questions about the right approach to region separation issues for loss resilience and other purposes.
Contributions relating to tile processing were suggested to be related.
Plan AHG.
An alternative solution is to have a semantic constraint on inter-layer prediction on slice boundaries rather than a normative decoder operation.
For further study to provide unified solution for slices and tile boundaries. General support for the concept, which was also supported in SVC.
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