Models of colour quality over a wide range of spectral power distributions

Abstract

Twenty-four real spectra were strategically structured to have systematic variation in average fidelity (IES R_f = 65, 75, 85, 95), average gamut (IES R_g = 80, 90, 100, 110, 120) and gamut shape (nominally saturating or desaturating red colour evaluation samples), at 3500 K. For each spectrum, 20 participants rated a set of objects along continuous scales of naturalness, preference, vividness and skin preference. Most of the top rated spectra, along all four scales, had average gamut greater than or equal to 100 (IES R_g ≥ 100) and did not desaturate red hues (IES R_cs,h16 ≥ 0%). Best fit models illustrate that average fidelity (i.e. IES R_f) and a proxy for red saturation (i.e. IES R_cs,h16, R_cs,h1) are salient derived measures. The results illustrate that a two-metric system of colour rendition, comprised of average metrics for fidelity and gamut, cannot fully describe colour quality and underscore the importance of a colour rendering graphic (i.e. IES Colour Vector Graphic). We propose and illustrate the utility of quantifying the shape of the IES TM-30-15 Color Vector Graphic with a best-fit ellipse.