Abstract not available in document
JVET-C0049 Extended deblocking-filter process for large block boundary [K. Kawamura, Q. Yao, S. Naito (KDDI Corp.)] [late]
This contribution proposes an extension of the deblocking filter process for large block boundaries. In HEVC, both large transform blocks and large prediction blocks were introduced. When a large block is used for a smooth area where luma value has little variation and/or gradation, blocking artefacts become more visible at low bit rates. In addition, when a texture region is coded by a large block with neighbouring blocks, the large block boundary is sometimes visible due to the difference of texture coding. For improving the visual quality, this contribution proposes an extension of the edge filtering process from six filtered samples to 14 filtered samples only for the boundary of large blocks. While BD-rate is degraded, the visual quality on large QP is reportedly subjectively improved.
Proponents were requested to organize a viewing session, such that other (independent) experts could confirm that quality improvement is visible. This should also include those sequences of class E LDB where a huge BD drop was observed. If a subjective benefit is reported, further study should be performed in the context of QTBT block structures.
The viewing session was organized, and the results are described as follows:
During the JVET-C meeting, a viewing session was conducted from 2 p.m. to 3 p.m. on 3 May, in the viewing room. Roughly 25 experts attended the viewing session. Two sequences from class B and one from class C with random access and low-delay B conditions were shown. One sequence from class E with low-delay B condition was also shown. Other sequences and conditions were shown based on further requests. It is noted that the display refresh rate is 59.94, and the displaying frame rates were set as 59.94 or 29.97 which was independent of the source sequences’ frame rate like 24 and 50fps. Experts noticed small differences between the video coded by JEM2.0 and the proposal; however, no clear judgement was possible whether those differences provide improvement or degradation in quality (both cases were observed). In class E, most experts had the opinion that some degradation like additional blockiness with small block sizes was recognized.
Further clarification (particularly in the context of QTBT) is needed whether a problem with deblocking of large block sizes exists, and if yes, whether it can be resolved without compromising quality in the case of small block sizes.