Quality evaluation of HEVC main still picture with limited coding tree depth and intra modes

In this paper we analyze the impact of limiting the number of modes in intra mode decision process and limiting the quad-tree structure of the coding unit (CU), prediction unit (PU) and transform unit (TU) on the quality of the High Efficiency Video Codec (HEVC) encoder supporting Main Still Picture (MSP) profile. A simplified HEVC encoder with coding-tree configuration such that the largest CU is of size 16×16 pixels with no further partitioning, PU and TU are of same size and with four intra modes- DC, Planar, Vertical and Horizontal, is used as a baseline to benchmark more complex HEVC encoder configuration supporting larger number of modes and deeper trees. Baseline encoder suffered an average quality loss of 0.86 dB when compared with HEVC encoder supporting all features. When largest coding unit (LCU) size is fixed at 16×16 pixels and modes are increased from 4 to 35, the average quality increase is of 0.72 dB. Similarly when the modes are fixed at 35 and LCU size is increased from 16 to 64, the average quality increase is of 0.51 dB. These results are interpretative in deciding optimal encoder configuration for achieving target objective quality.