Mirroring of coefficients for Transform Skipping in Video Coding

This paper studies the Transform Skip option of the emerging High Efficiency Video Coding (HEVC) standard, and presents a modification to the ordering of coefficients within a transform skipped residual block. Depending on the scanning order for the given block, the coefficients are rearranged relative to their original spatial positions. The rearrangement is achieved by mirroring the coefficients across one of the block diagonals. When the diagonal scan is used, mirroring across the anti-diagonal is used, otherwise mirroring across the main diagonal (transpose) is used. In this way the distribution of significant coefficients is closer to the distribution in a case when transform is applied. Therefore the entropy coding may benefit from the new arrangement. The experiments show BD-rate gains of up to 2.4% for Screen Content sequences.