Pseudo-2D-matching based enhancement to high efficiency video coding for screen contents

Computer screens are rich in discontinuous-tone content besides traditional continuous-tone content. Thus, new video coding tools coherently united into traditional hybrid coding tools are needed to effectively compress screen contents. This paper proposes a Pseudo-2D-matching (P2M) coder based enhancement to High Efficiency Video Coding for screen contents. An input Largest Coding Unit (LCU) is simultaneously fed into a P2M coder and a traditional hybrid coder. The coder minimizing rate-distortion is selected as the final coder for the LCU. The P2M coder breaks an LCU into many horizontal or vertical line segments and searches matching line segments in the searching-window consisting of previously coded pixels. Since the searching-window is large (a few kilobytes to megabytes) to increase the chance to find a good matching, a hash-table is used to speedup the search. In the P2M coder, three matching modes are used: 1) vertically scanned string matching; 2) horizontally scanned 2D-shape-preserved matching; and 3) vertically scanned 2D-shape-preserved matching. All three matching modes are used to code an LCU and the mode minimizing rate-distortion is selected in the P2M coder. The P2M based enhancement achieves significant Bitrate-distortion rate (BD-rate) and subjective visual quality improvement over traditional hybrid coding for screen contents.