Improved hierarchical quantisation parameter setting method for screen content coding in high efficiency video coding

Screen content video (SCV) is generated by computers, including texts, animation, and graphics. Unlike conventional camera-captured video, screen contents are often discontinuous, as some regions may remain static for successive frames. Therefore, the traditional hierarchical quantisation parameter (QP) setting scheme for conventional video may be not efficient enough for SCV. In this study, an improved hierarchical QP setting method is proposed for screen content coding. Based on the default hierarchical QP setting in high efficiency video coding (HEVC), the proposed method adjusts QP values at the coding tree unit level according to block matching and content complexity. Smaller QP is assigned to the static region and the translational region to reduce quality refinement, and bigger QP is assigned to the complex and limited quality propagated region to save bits. Experimental results show that compared with the default QP setting method in HEVC, the proposed method reduces up to 15.7% bitrate and 6.3% bitrate on average, and decreases the encoding time by 9.2% averagely.