Fast transform skip mode decision for HEVC screen content coding

This paper investigates a fast transform skip mode decision method which can reduce residual coding complexity of a transform skip tool for SCC (Screen Content Coding) extension of HEVC (High Efficiency Video Coding). Noticing the high tendency of transform skip mode occurring in 4×4 transform blocks in a coding unit (CU) coded as the intra block copy, the proposed fast method is designed to select either transform skip or coded block flag being zero for 4×4 blocks in a CU coded as intra block copy. Experiments verify reduction of total encoding time by average 3.0% and 4×4 transform block encoding time by 28.2% with only a slight increase of BD-rate by 0.22%. In addition, a modified transform skip mode signaling method is designed in order to minimize the coding efficiency loss due to the proposed fast mode decision. It shows reduction of total encoding time by 2.9% on average and encoding time of 4×4 transform block by 27.6% with only 0.05% BD-rate degradation.