Affine Deformation Model Based Intra Block Copy for Intra Frame Coding

In intra frame coding, many methods are proposed to reduce spatial redundancy, including angular intra prediction and intra block copy. However, these two methods cannot deal with complex structure redundancy, such as scaling and rotation relationship where spatial structures are the same but sizes and orientations are different, leading to limited coding efficiency. In this paper, we first mathematically prove that 4-parameter affine deformation model can describe this complex relationship. Then we propose an affine deformation model based intra block copy (ADMIBC) scheme. In the scheme, we focus on several problems, including a fast displacement vector validity judgement algorithm to reduce encoding time, a padding method for unavailable reference pixels during sub-pixel interpolation to improve prediction accuracy and candidate list building methods of control point displacement vector predictor to reduce coding bits. Experimental results show that ADMIBC achieves up to −2.16% BD-rate reduction and −0.99% on average in all intra configuration, compared to the latest video coding standard Versatile Video Coding (VVC).