The Joint Collaborative Team on Video Coding (jct-vc) of itu-t wp3/16 and iso/iec jtc 1/ sc 29/ wg 11 held its tenth meeting during 11-20 July 2012 at the City Conference Centre (ccc), a k. a

5.16.2Chroma modes

JCTVC-J0052 Bug-fix of intra chroma DM mode for Intra_NxN with SCU size larger than 8x8 [T.-D. Chuang, Y.-W. Huang, Y.-H. Huang, T.-A. Lin, K.-B. Lee, C.-C. Ju, S. Lei (MediaTek)]

A mismatch between HM-7.0 software and HEVC text specification draft 7 is reported as follows. In the HM-7.0 software, an intra CU sends only one intra chroma prediction mode regardless of the PU partition mode. However, in the text specification (JCTVC-I1003_d4.doc), an intra CU sends one intra chroma prediction mode for each chroma PU, which is inconsistent with HM-7.0 software when NxN PU partition mode is selected. The inconsistency needs to be resolved.

Two possible solutions are reported here. Method 1 follows more or less what is in the software but includes a bug fix to let the four chroma PUs refer to the four different luma PUs when the intra CU is an SCU larger than 8x8 in luma and DM mode and NxN PU partition mode are selected. It is reported to achieve 0.0–0.6% luma coding gains and −0.1–1.0% chroma coding gains when the SCU size is set to 16x16 in luma. Method 2 follows what is specified in text but includes a bug fix to send only one intra chroma prediction mode when the intra CU is an SCU equal to 8x8 in luma and DM mode and NxN PU partition mode are selected. It is reported to achieve 0.0–0.4% luma coding gains and 0.6-2.4% chroma coding gains for when the SCU size is set to 16x16 in luma.

Matched software and text are provided for both methods. It is proposed to adopt one of the proposed methods as a bug-fix to the current HEVC.

Results are presented with SCU 16x16 as for 8x8 (common test conditions) no effect would be visible

What is suggested here is less a “bug fix” than a new proposal which suggests to derive different prediction modes for the case where several chroma PBs are contained in a CU. The decision of last meeting was to use only one chroma prediction mode (i.e. only one prediction direction etc. for all chroma PBs) within a CU. This was extensively discussed and it was confirmed that currently software and text are aligned.

No action.