History Based Block Vector Predictor for Intra Block Copy

The third generation of the audio video coding standard (AVS3) is the latest standardization developed by Audio Video Coding Standard Working Group of China on the basis of IEEE 1857.4. It is well known that Intra Block Copy (IBC) significantly improves the coding efficiency of screen content videos which utilizes a block vector to identify a similar block in current reconstructed picture. However, how to better code the block vectors need to be explored. In this paper, we propose a history-based block vector prediction (HBVP) method for better coding block vectors associated with the IBC mode. Inspired by the history-based motion vector design, motion information of previously IBC-coded blocks is maintained in a table and used as BVP for the current block in IBC mode. Thanks to the HBVP, the encoder only needs to signal the HBVP index and block vector difference of an IBC coded block to the decoder, which significantly enhance the coding efficiency of IBC mode. Experimental results show that the proposed method achieves −9.43 % (TGM)/ −5.77 % (MC)/ −0.27% (G) BD rate reduction in IBC-BVD mode and −12.34% (TGM)/ −8.43% (MC)/ −0.57% (G) BD rate reduction in IBC-SKIP/DIRECT mode for SCC sequences in AI configurations with limited encoding-time increase, on the latest AVS reference software platform. The proposed methods were partially adopted by AVS3.