High dynamic range video compression by intensity dependent spatial quantization in HEVC

The Human Visual System (HVS) shows non-linear sensitivity to the distortion introduced by lossy image and video coding. This non-linear sensitivity is due to luminance masking, contrast masking and the spatial and temporal frequency masking phenomena of the HVS. This paper proposes a perception-based quantization method that exploits luminance masking in the HVS in order to enhance the performance of the High Efficiency Video Coding (HEVC) standard for the case of High Dynamic Range (HDR) video content. A profile scaling based on a tone-mapping curve computed for each HDR frame is introduced. The quantization step is then perceptually tuned on a Transform Unit (TU) basis. The proposed method has been integrated into the reference codec considered for the HEVC range extensions and its performance was assessed by measuring the bitrate reduction against the codec without perceptual quantization. The HDR-VDP-2 image quality metric was employed to measure the compressed picture quality. For the same quality level, an average bitrate reduction of 9% is achieved across all tested HDR sequences.