Prediction mode based reference line synthesis for intra prediction of video coding

Intra prediction is a significant coding tool that allows a high level of video compression to be achieved in the current state-of-the-art video coding standard, High Efficiency Video Coding (HEVC), and the joint exploration model (JEM) developed by the Joint Video Exploration Team (JVET) of ITU-T VCEG and ISO/IEC MPEG for the next generation video coding standard. In intra prediction, the top and left adjacent lines to the current coding block in the neighboring reconstructed blocks are selected as the reference lines. However, it has been observed that the adjacent reference line might not always provide optimal prediction due to the quantization noise and object occlusions caused by straight lines. In this paper, we propose the synthesis of another reference line by integrating multiple lines in the neighboring reconstructed blocks based on the prediction mode. The synthesized line and the reconstructed adjacent line compete in the rate distortion optimization process, where the line that yields a minimum cost is finally selected. The proposed method is implemented on top of JEM 3.0, and the experimental results show that −0.29% (average), −1.15% (maximum) luma BD gain and −0.15% (average), −0.59% (maximum) luma BD gain can be achieved in all intra and random access conditions, respectively, among all the test sequences.