Inter-layer information derivation (1)
Discussed 01-09 p.m. (JRO).
14.1.97.1.1.1.1.1.281JCTVC-P0049 AHG 13: Scale and reference position derivation for sub-region extraction [T. Yamamoto, T. Tsukuba, T. Ikai (Sharp), E. Alshina (Samsung)]
When a bitstream is generated by extracting the sub region of the original picture, the reconstructed pixel values could be changed if scale and/or phase are not preserved. This contribution proposes 1) new syntax in SPS extension and 2) modified scale and reference pixel location derivation. The proposed changes help keeping the same scale and phase, and thus useful for the applications using sub-region extraction.
The method had been presented before as O0056, and further study had been performed in AHG13 (inter-layer filtering). During this, some more improvement of the method was achieved.
This is only relevant for a case where an ROI is extracted from both the base and enhancement layer (where the enhancement layer ROI cannot cover a larger area than the base layer ROI).
In principle, the same thing could be achieved with the current scaled ref layer offset, but not guaranteed at any combination of sample position of base and enhancement layers (where the allowed positions have some restriction due to CTU boundaries anyway).
It was also mentioned that something similar can be achieved by the ILCTS SEI message, and it is unclear what the additional benefit of the proposed method is.
Questions were raised about the relevant use cases that require the high accuracy of region extraction. More information about this was requested.
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