| JCTVC-J0275 Non-CE1: DST quantization matrix syntax for CE1 Simplification 2 [R. Cohen, A. Vetro (MERL)]
Core Experiment 1 (CE1) is testing two simplifications: Simplification 1 uses the 2-D DST for 4x4 luma Intra transform block, and Simplification 2 is the same except that the 2-D DCT is used when the Intra prediction mode is DC. The purpose of this contribution is to re-propose the syntax in JCTVC-I0419, which supports an additional scaling list for 4x4 luma Intra transform blocks, in case Simplification 2 of CE1 is adopted. This syntax supports two default scaling lists for 4x4 luma Intra transform blocks: one associated with the DCT and the other associated with the DST. It is reported that because Simplification 2 of CE1 does not apply the DCT and DST together in the same 4x4 transform block, it is not necessary to switch between the two scaling lists in a transform block.
Proposes the syntax in JCTVC-I0419, which supports a separate scaling list for 4x4 luma Intra transform blocks – one for the DCT residual case and one for the DST residual case – in the context of the case of "simplification 2" of CE1.
It was asked whether any visual benefit had been shown for this.
The statement made at the last meeting, that a switching of quant matrices dependent on intra mode at 4x4 block level is undesirable, is still valid.
Some doubt was raised whether usage of a separate quantization matrix for 4x4 DST does provide a visually distinguishable benefit (the proposed matrices are quite similar between DCT and DST anyway)
The question was also raised how suitable the current DCT default matrices are, as in practice most implementers would use own matrices with adaptation to the video material characteristics.
If CE1 simplification 1 would be adopted, matrices do not need to be switched, but even in that case the current default matrix should be retained, as no evidence was shown (in terms of visual testing) that it is not appropriate for the 2D DST.
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