  Due to the spectral sensitivity phenomenon of the Human Visual System (HVS),
the color channels of raw RGB 4:4:4 sequences contain significant psychovisual
redundancies; these redundancies can be perceptually quantized. The default
quantization systems in the HEVC standard are known as Uniform Reconstruction
Quantization (URQ) and Rate Distortion Optimized Quantization (RDOQ); URQ and
RDOQ are not perceptually optimized for the coding of RGB 4:4:4 video data. In
this paper, we propose a novel spatiotemporal perceptual quantization technique
named SPAQ. With application for RGB 4:4:4 video data, SPAQ exploits HVS
spectral sensitivity-related color masking in addition to spatial masking and
temporal masking; SPAQ operates at the Coding Block (CB) level and the
Prediction Unit (PU) level. The proposed technique perceptually adjusts the
Quantization Step Size (QStep) at the CB level if high variance spatial data in
G, B and R CBs is detected and also if high motion vector magnitudes in PUs are
detected. Compared with anchor 1 (HEVC HM 16.17 RExt), SPAQ considerably
reduces bitrates with a maximum reduction of approximately 80%. The Mean
Opinion Score (MOS) in the subjective evaluations, in addition to the SSIM
scores, show that SPAQ successfully achieves perceptually lossless compression
compared with anchors.
