Hue Coefficient of Equivalent Lightness Formulas

The empirical formulas introduced in our previous paper to calculate the equivalent lightness of colored surfaces when their Munsell color notations were known had a problem with the contribution of hue to the chromatic lightness particularly in the region of hue 5Y. We present a new formula for hue coefficient h (φ). The revised formula for equivalent lightness nicely describes our old experimental results and our new ones making it useful in predicting the equivalent lightness of any colored objects if they are specified by the Munsell color notations. As additional experiment, the color naming experiment was conducted for the color charts used in the equivalent lightness experiment and the chromatic lightness was found to be mainly determined by the amounts of unique hue components, red, green, and blue, but not by yellow.