Reverse scan for transform skip mode in HEVC codec

High Efficiency Video Coding (HEVC) is being developed by Joint Collaborative Team on Video Coding (JCTVC). HEVC has transform skip mode which is only applicable to 4×4 TUs (Transform Units). Transform process is skipped when this mode is selected. By introducing transform skip there is significant gain in coding efficiency for F class sequences [1][2]. In this paper it is proposed that before variable length encoding of the transform skip cases, reverse the scanning of the residual of 4×4 block sizes. Due to this modification it is observed that coding efficiency further increased on an average by 1.6% in terms of bd-rate [3] for class F sequences in all intra (AI) testing configurations. For other GOP structures like RA (random access), low delay with B pictures (LB), and low delay with P pictures (LP) average-bit-rate gains are 1.1%, 0.64% and 0.57% respectively. Due to this change there is a negligible impact on encoding/decoding time.