Intra prediction using adaptive TU scan order with residue flipping

This paper proposes an adaptive scan order of intra prediction on High Efficiency Video Coding (HEVC). In HEVC, prediction, transformation and quantization are applied in a z-scan order consistently. The proposed method modifies the z-scan order when intra prediction direction is set to from top-right to bottom-left or from bottom-left to top-right, which is corresponding to intra prediction mode from 2 to 9 or from 27 to 34 of HEVC specifications. By the modification of z-scan order, the lower/right neighboring samples can be newly utilized as reference samples, so that the accuracy of intra prediction is improved. Additionally, the residual signals are flipped vertically or horizontally in accordance with the modified z-scan order. The experimental result shows -0.2%(Y), -0.4%(U) and -0.3%(V) BD-rate gain in an all intra configuration case, compared with HEVC with slight increase of encoding and decoding time.