JVET-M0277 Fixes of enabling pcm_loop_filter_disabled_flag with pcm mode signalling under dual tree partition [L. Zhang, K. Zhang, H. Liu, J. Xu, Y. Wang, P. Zhao, D. Hong (Bytedance)]
In current VVC, PCM mode flags for luma and chroma components are signalled separately when dual tree partition is enabled. However, when the pcm_loop_filter_disabled_flag is enabled, determination of enabling/disabling SAO filtering process for chroma blocks is wrongly based on the signalled PCM mode flag for luma blocks. In addition, ALF is performed even when pcm_loop_filter_disabled_flag is true. In this contribution, these two issues are fixed wherein whether to filter a block is dependent on the signalled PCM mode flag for the associated color component. Simulation results reportedly show that there is no performance changes under common test conditions.
Decision (BF/text): Include disabling ALF as a third loop filter when the pcm_loop_filter_disabled_flag is set, as suggested in JVET-M0277.
Decision (BF/SW): Disable SAO and ALF in chroma part when dual tree is used and the flag is set, and disable ALF in luma part when dual tree is used and the flag is set, as suggested in JVET-M0277.
Some experts commented that it might be better to get rid of PCM mode, as it is hardly used in practical encoders. This issue was also shortly raised in the closing plenary; it could be an action item for future consideration.