Advancements in intra prediction techniques beyond AV1 codec
Jing bo Ye, Liang Zhao, Xin Zhao, Han Gao, Shan Ting Liu · 2023
Smooth prediction modes and angular intra prediction modes are two major types of intra prediction modes in AV1 video codec designed to reduce spatial redundancy in video signals. The smooth prediction mode is particularly effective in predicting blocks with a smooth gradient within the block, while angular intra prediction mode predicts pixel values by a weighted average of neighboring pixels along different angular directions within the block. This paper proposes extensions to these modes to improve the intra coding performance towards a next-generation video codec beyond the AV1 codec. The first extension involves refining the smooth modes by considering the geometric distance between each sample and its reference pixels to achieve more precise prediction. The second extension involves refining the distribution of intra prediction angles in AV1 such that the intra prediction angles are denser around vertical and horizontal modes and coarser around diagonal directions. The third extension proposes applying Intra Bi-Prediction (IBP) to a subset of prediction angles, which implicitly allows the codec to choose between IBP on and off case. Experimental results show that the proposed methods achieve up to 0.3% luma and chroma average BD-rate savings with no encoding time increase for all intra configuration when compared to research-v4.0.0 tag of reference software AVM which is developed for exploring next-generation video coding beyond AV1. Notably, the highest coding gain observed was up to 1.5% for 4K video sequences.