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

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.