International organisation for standardisation organisation internationale de normalisation

5.16.2Last coefficient flags (x and y)

5.16.2.1.1.1.1.1.1JCTVC-H0514 Chroma Context reduction for Last Coefficient Position Coding in HEVC [X. Fang, K. Panusopone, L. Wang (Motorola Mobility)]

This document described the implementation and reported the results of a proposed chroma context reduction for last coefficient position coding. Two context index assignments were proposed. The first version uses the same contexts for 4x4 and 8x8 chroma TUs and the second version uses the same contexts for all chroma TUs.

One comment was that the current design is quite regular and in common for luma and chroma coding, and concluded that we have no reason to change this.

5.16.2.1.1.1.1.1.2JCTVC-H0627 Cross-check of Motorola proposal on chroma context reduction for last coefficient position coding (JCTVC-H0514) [H. Yang, H. Yu (Huawei)] [late 02-01]

5.16.2.1.1.1.1.1.3JCTVC-H0537 CABAC Contexts Reduction for Last Position Coding [L. Guo, W.-J. Chien, X. Wang, M. Karczewicz (Qualcomm)]

In this proposal, a method to reduce the contexts for last position coding was proposed. First, a single context is proposed to be used for the last bins (with context) from different block sizes; Second, chroma 8x8 and 16x16 blocks share the same set of contexts for last position coding. It was reported a total context savings of 16 (from 60 to 44) contexts was achieved. Experimental results reportedly show that there is 0.0% Y-BD bit rate change under the common test conditions.

One comment was that even though the number of contexts is lower, the regularity of the table is reduced (for luma), which may be a problem with implementations (e.g. optimized code of reference software).

Other experts expressed the opinion that the reduction of number of contexts is beneficial.

Decision: Adopt combination of H0537 luma and H0514 chroma (version with 3 contexts) – results are identical and a combined WD text was made available in a new version of JCTVC-H0514.

5.16.2.1.1.1.1.1.4JCTVC-H0612 Crosscheck of Qualcomm proposal (JCTVC-H0537) on CABAC Contexts Reduction for Last Position Coding [K. Sugimoto, A. Minezawa, S. Sekiguchi (Mitsubishi)] [late]