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

JCTVC-M0407 Cross-check of modified in-loop colour-space transformation (JCTVC-M0072) [K. Kawamura, S. Naito (KDDI)] [late]
JCTVC-M0080 AHG7: Post filtering for colour-space transformation [M. Matsumura, S. Matsuo, S. Takamura, H. Fujii, A. Shimizu (NTT)]

(Discussion chaired by D. Flynn.)

To reduce the redundancy among Y-Cb-Cr/R-G-B components, an in-loop color-space transformation method was proposed in JCTVC-L0371. In this contribution, a post filter which replaces the in-loop colour-space transformation with post processing is proposed. The overall average coding gains based on GBR BD-rate compared to the anchor (HM10.0 RExt. 2.0) of 23.8% / 13.5% / 7.5% (AI main-tier / high-tier / super-high-tier), 33.2% / 12.7% (RA main-tier / high-tier), and 33.4% / 18.5% (LD-B main-tier / high-tier) were confirmed. The average run-times of encoding and decoding (including pre/post filtering) were 86.0% and 90.3%, respectively.

The in-loop colour-space transform proposal involves computing the SVD of reference samples to derive a matrix to be used in the transmission of a particular CU. One potential problem with such a system is the coupling of luma and chroma components in the critical path of the reconstruction process. This proposal suggests removing the per CU decoder matrix derivation process and instead to signal a single matrix for use with a particular picture in an SEI message. The decoder may then implement this prior to picture output.

It was remarked that an SEI message may not be the most appropriate method for signalling such important information, as the loss of a message will cause severe rendering issues through use of the wrong colour matrix.

While no results were presented for YCbCr sequences, the proponent reported that the technique does not work very well in this configuration (typically having no effect).

Further results were presented that examined how this technique compared against using a fixed colour transform at the input to the encoder. It appears to have a similar performance to that of JCTVC-M0048 (YFbFrv), which would be a far simpler proposition.

No action.