Fundamental scales of hue appearance and discrimination

Abstract Hue can be described with two types of scales. The first, for hue discrimination, is of the form of a hue angle metric such as found in the Munsell and CIELAB systems. The second, for hue appearance, is in the form of a hue quadrature metric as found in the NCS system and color appearance models such as CIECAM16. Any useful hue metric should also exhibit hue constancy – the important concept that stimuli of various lightness and saturation, but identical hue designations appear to be of the same hue. Hue angle in the IPT color model has repeatedly been shown to very well describe contours of constant hue and has been rigorously tested over more than two decades. However, the IPT model was not designed with hue spacing, for either discrimination or appearance, in mind. This paper describes the derivation of a fundamental and physiologically plausible model, called FHS for Fundamental Hue Scales, with predictors for both hue discrimination and hue appearance built directly from cone fundamentals and with hue linearity as good as that found in IPT. Such a model can be used with individual LMS color matching functions as the basis for the hue dimension of improved, and individualized, color appearance scales.