Improved intra transform skip mode in HEVC

Recent years we have witnessed a striking rise of the compound video, which is generated by computers. The High Efficiency Video Coding standard (HEVC) adopts the intra transform skip mode to improve the coding efficiency of compound video. In this paper, we improve the intra transform skip mode from two aspects. Firstly, we study the statistical character of the intra prediction residual and propose a separate coefficient scan order for the intra transform skip mode. Secondly, we analyze the probability of the intra transform skip mode for different coding unit (CU) sizes and prediction unit (PU) sizes, and then propose one limitation to reduce the applied range of intra transform skip mode. The experimental results show that the first method can achieve 1.6%, 1.1%, and 0.7% luma coding gains on average in terms of BD-rate for class F under HE10-AI, HE10-RA, and HE10-LB conditions respectively; the second method can bring 9% encoder run time reduction with almost the same BD-rate changes. The proposed methods have been partially adopted into HEVC standard.