JVET-X0063 AHG10: Deblocking filter setting for VTM [H. Zhang, X. Li, S. Liu (Tencent)]

In this contribution, a set of encoder-only settings of deblocking filter are proposed for VTM. Basically, the deblocking filter control parameters BetaOffset_div2 and TcOffset_dive2 are adjusted based on temporal layer ID for both luma and chroma components. The proposed method is implemented by only modifying VTM configuration files. It is reported that under the CTC, compared with VTM-14.0, the overall performance are as follows:

• AI: -0.74%/-0.69%/-0.44% with 99%EncT/99%DecT
• RA: -0.32%/-0.58%/-0.50% with 100%EncT/100%DecT
• LDB: -0.62%/-0.41%/0.02% with 100%EncT/100%DecT
• LDP: -0.34%/-0.26%/-0.09% with 100%EncT/100%DecT

In ECM, a similar setting is used, but it is further controlled by additional syntax elements. In VTM, the different settings for different temporal layers can be controlled via slice header. One intent of the proposal is making the comparison of VTM and ECM more fair.

Visual quality impact should be investigated before such a change is applied. Deblocking settings are known to be sensitive in terms of visual quality, even when showing BD gains.

Only requires a config file change, no encoder software change.

It is pointed out that also ECM has not been investigated in terms of visual quality, but even if visual problems were found in VTM, it might not be the case in ECM. Both VTM and ECM should be checked regarding visual impact of the method.

Further study was recommended (coordinated with M. Wien to prepare a visual investigation at next meeting).