Beyond colour gamuts: Novel metrics for the reproduction of photoreceptor signals

Abstract

Colour gamuts describe the chromaticity reproduction capabilities of a display, i.e. its ability to reproduce the relative cone excitations from real-world radiance spectra. While the cones dominate “canonical” visual function (i.e. perception of colour, space, and motion) under photopic light levels, they are not the only photoreceptors in the human retina. Rods and melanopsin-containing intrinsically photosensitive retinal ganglion cells (ipRGCs) also respond to light and contribute to both visual and non-visual light responses, including circadian rhythms, sleep-wake control, mood, pupil size, and alertness. Three-primary display technologies, with their focus on reproducing colour, are not designed to reproduce the rod and melanopsin excitations. Moreover, conventional display metrics used to characterize three-primary displays fail to describe the display’s ability (or inability) to reproduce rod and melanopsin excitations, and thus do not capture the display’s ability to reproduce the full human physiological response to light. In this paper, three novel physiologically relevant metrics are proposed for quantifying the reproduction and distortion of the photoreceptor signals by visual displays. A novel equal-luminance photoreceptor excitation diagram is proposed, extending the well-known MacLeod-Boynton chromaticity diagram, to allow visualizations of the five-dimensional photoreceptor signal space in a three-dimensional projection.

Psychophysics: Concepts, methods, and frontiers.

“…The intrinsically photosensitive retinal ganglion cells (ipRGCs), which are known to be involved in driving nonvisual responses to light, such as circadian rhythms, sleep-wake control, mood, pupil size, and alertness, express the shortwavelengthsensitive photopigment melanopsin and encode environmental light intensity independent of the cones and rods (but also receive synaptic input from cones and rods) (Do, 2019;Lucas et al, 2014;Provencio et al, 2000;Spitschan, 2019). Conventional threeprimary color displays do not allow for the reproduction and control of rod and ipRGC signals, requiring at least five photoreceptor classes (Hexley et al, 2021). Generating stimuli that stimulate only one photoreceptor class (while producing no signal in another set of classes) is done using the method of silent substitution (Estévez & Spekreijse, 1982;Spitschan & Woelders, 2018).…”