Block-Composed Background Reference for High Efficiency Video Coding

A block-composed background reference method is proposed in this paper for High Efficiency Video Coding (HEVC). For a group of picture (GoP), the first reconstructed picture is served as an initial background reference, which probably includes foreground content. In the subsequent coding, some background coding tree units (CTUs) in every picture are selected to be compressed with high quality. These reconstructed CTUs are used to update the background reference as well as replace the foreground content. Finally, a high-quality background reference is generated to better exploit the long-term temporal correlation in the video. There are three key technical contributions in the proposed coding scheme. First, the background reference is generated gradually by block updating instead of picture updating, which makes the scheme free of bit-rate burst and more suitable for real-time applications and can generate high-quality background reference even with complicated foreground. Second, we propose an approach to select background CTUs by taking both temporal and spatial smoothness into account. Third, we propose a model to decide the coding parameters of the selected background CTUs based on the overall picture activity, which essentially pursues the GoP-level optimal performance when making CTU-level decision. The proposed background reference is implemented into HEVC, and the experimental results demonstrate a significant improvement in coding efficiency. Compared with HEVC, our method can averagely save 14% bits in surveillance and conferencing sequences with negligible increase of encoding and decoding complexity. In particular, it can still averagely save 7.3% bits in HEVC general test sequences. Obviously, the proposed scheme can be applied to more general video contents.