Improving inter prediction in HEVC with residual DPCM for lossless screen content coding
Video content containing computer generated objects is usually denoted as screen content and is becoming popular in applications such as desktop sharing, wireless displays, etc. Screen content images and videos are characterized by high frequency details such as sharp edges and high contrast image areas. On these areas classical lossy encoding tools - spatial transform plus quantization - may significantly compromise their quality and intelligibility. Therefore, lossless coding is used instead and improved coding tools should be specifically devised for screen content. In this context this paper proposes a residual differential pulse code modulation (RDPCM) applied to inter predicted residuals and tested in the context of the HEVC range extension development. The proposed method exploits the spatial correlation present in blocks containing edges or text areas which are poorly predicted by motion compensation. In addition to the baseline inter RDCPM, two improvements to the compression efficiency and the overall throughput are presented and assessed. When compared to HEVC lossless coding as specified in Version 1 of the standard, the proposed algorithm achieves up to 8% average bitrate reduction while not increasing the overall decoding complexity.