Symmetric intra block copy in video coding

In the screen content coding extension for HEVC, intra block copy (IBC) was adopted to explore the redundancy between reduplicated patterns, which often occurs in a picture with screen contents. Besides reduplication, symmetry is also often observed in screen-content and even in natural pictures. In this paper, symmetric intra block copy (SIBC) is therefore proposed to further improve IBC. By flipping the reference block of IBC horizontally or vertically, SIBC may provide better predictions than IBC for symmetric patterns. Experimental results show that SIBC can achieve 1.2% and 1.9% coding gains in all intra configurations on sequences in the category of YUV, text & graphics with motion, 1080p for lossy and lossless coding respectively.