Intra motion compensation and entropy coding improvements for HEVC screen content coding

Applications such as wireless displays, automotive infotainment, remote desktop, remote gaming, distance education, cloud computing etc. are becoming popular. Video in these applications often has mixed content consisting of natural video and screen content (text, graphics etc.) in the same picture. In text and graphics regions, patterns such as text characters, icons, lines etc. can repeat within a picture. Also since the graphics and text regions have sharp edges that are sometimes not predicted well by Intra prediction tools, the probability of prediction error having high amplitude increases. This paper presents two tools for improving the intra coding efficiency of the High Efficiency Video Coding (HEVC) standard when coding screen content. The first tool is a Coding Unit (CU)-level Intra motion compensation tool to eliminate redundancy from repeating patterns in text and graphics regions. The second tool is a modification to HEVC cRiceParam update process of coeff_abs_level_remaining entropy coding to adapt better to larger prediction errors in text and graphics regions. The combination of the two tools achieves an average bit-rate/Bjontegaard Delta-Rate savings in the range of 0.8% to 28.1% over HEVC Range Extensions Test Model on screen content test video sequences used in Range Extensions core experiments by the Joint Collaborative Team for Video Coding (JCT-VC).