Reduced-complexity intra block copy (IntraBC) mode with early CU splitting and pruning for HEVC screen content coding

Abstract

A screen content coding (SCC) extension to high efficiency video coding has been developed to incorporate many new coding tools in order to achieve better coding efficiency for videos mixed with camera-captured content and graphics/text/animation. For instance, the Intra Block Copy (IntraBC) mode helps to encode repeating patterns within the same frame while the Palette mode aims at encoding screen content with a few major colors. However, the IntraBC mode brings along high computational complexity due to the exhaustive block matching within the same frame though there are already some constraints and fast approaches applied to the IntraBC mode to reduce its complexity. Thus, we propose a fast intracoding scheme to reduce the complexity of using the IntraBC mode in SCC. Screen content always contains no sensor noise resulting in the characteristics with pixel exactness along both horizontal and vertical directions. These characteristics pave the way for mode skipping and early coding unit (CU) splitting. Besides, early CU pruning and early termination are proposed based on the rate distortion cost to further reduce encoder complexity. Moreover, we also propose reducing the complexity of the IntraBC mode by checking the hash value of each block candidate and the current block during block matching. With our proposed scheme, the encoding time is reduced compared with the SCC while the coding efficiency can still be maintained with a minor increase in the bjontegaard delta bitrate.