  There exists an intrinsic relationship between the spectral sensitivity of
the Human Visual System (HVS) and colour perception; these intertwined
phenomena are often overlooked in perceptual compression research. In general,
most previously proposed visually lossless compression techniques exploit
luminance (luma) masking including luma spatiotemporal masking, luma contrast
masking and luma texture/edge masking. The perceptual relevance of color in a
picture is often overlooked, which constitutes a gap in the literature. With
regard to the spectral sensitivity phenomenon of the HVS, the color channels of
raw RGB 4:4:4 data contain significant color-based psychovisual redundancies.
These perceptual redundancies can be quantized via color channel-level
perceptual quantization. In this paper, we propose a novel spatiotemporal
visually lossless coding method named Spectral Perceptual Quantization
(Spectral-PQ). With application for RGB 4:4:4 video data, Spectral-PQ exploits
HVS spectral sensitivity-related color masking in addition to spatial masking
and temporal masking; the proposed method operates at the Coding Block (CB)
level and the Prediction Unit (PU) level in the HEVC standard. Spectral-PQ
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), Spectral-PQ considerably reduces bitrates with a maximum reduction of
approximately 81%. The Mean Opinion Score (MOS) in the subjective evaluations
show that Spectral-PQ successfully achieves perceptually lossless quality.
