JVET-P0270 Non-CE7: Modified signalling method of cu_cbf and tu_cbf_luma [D. -J. Won, J. -M. Ha, J. -H. Moon (Sejong university)]
This contribution proposes a modified signalling method for cu_cbf and tu_cbf_luma syntax when the current tree type is equal to dual tree and the current coding unit is coded by MODE_IBC. In MODE_IBC of the current VVC draft 6, the cbf information for luma is signaled by cu_cbf in the dual tree. while in the other coding modes, the cbf information for luma is signaled by tu_cbf_luma in Transform unit syntax. It is inconsistent in terms of the semantics of encoding the syntax. This contribution presents a signalling method in which cu_cbf is signaled only when the current tree type is single tree and the cbf information for luma of the current block coded by MODE_IBC in dual tree is informed by tu_cbf_luma. And an additional context for tu_cbf_luma is added to minimize a coding loss.
In Test 1, only syntax changes on cu_cbf and tu_cbf_luma are applied. In Test 2, additional context is added for tu_cbf_luma based on Test 1. Under the AI CTC configurations with IBC being on, the average (Y, U, V) BD rate performances of the proposed are reported with negligible encoding and decoding time change as follows:
Test 1 - VTM6.0-AI: {(Y, U, V)-BD-rate = (0.00%, 0.00%, 0.05%), EncT = 101%, DecT = 99%}
Test 2 - VTM6.0-AI: {(Y, U, V)-BD-rate = (0.00%, -0.02%, 0.03%), EncT = 101%, DecT = 100%}
It was not obvious that there is a problem. The purpose of cu_cbf is sufficiently understandable in the spec.