Perceptual Colour Difference Uniformity in High Dynamic Range and Wide Colour Gamut

Perceptual uniformity is a highly desirable property of colour spaces or colour difference measures where equal level in colour value difference should result in equal perceptual difference. Designing colour spaces or colour difference measures of perceptual uniformity is a long standing problem in colour science. This has become increasingly important with the growing popularity of high dynamic range (HDR) and wide colour gamut (WCG) cameras, content and displays. We design an efficient testing framework to evaluate perceptual uniformity by subjective just noticeable difference (JND) measurement at a wide range of luminance levels followed by coefficient of variation (CV) computation. We carry out subjective testing on RGB, $\mathrm{x}\mathrm{y}\mathrm{Y}, \mathrm{L}^{*}\mathrm{a}^{*}\mathrm{b}^{*}$, YCbCr, CIECAM02-UCS and ICtCp colour spaces and $\triangle$E2000 metric in ITU-R BT 2020 colour gamut across a wide range of luminance levels (from 0.01 to 500 nits) using a professional HDR/WCG display in a carefully controlled dark testing environment. Our results suggest that on average, the ICtCp space performs the best in the current test, but is still distant from achieving perceptual uniformity.