Abstract
Hue scaling techniques aim to describe colour in terms of the relative amounts of unique hues, which are usually defined verbally rather than perceptually. We have developed a hue scaling technique which neither involves hue naming, nor requires observers to estimate the amount of unique hues in compound colours.
It is based on the partial colour matching method (Logvinenko, VSS 2006) which implies judging whether two colours have a common component hue. As proved elsewhere (Logvinenko, VSS 2006), the largest sets of colours which partially match each other - chromaticity classes - are in one-to-one correspondence with component hues. Specifically, each chromaticity class comprises all colours having the same component hue.
Using 482 chips from the boundary of the Munsell tree, we have evaluated chromaticity classes for normal trichromats. The results are in line with the classical six unique hues. Observers were asked to order the chips within each chromaticity class in terms of the strength of the component hue constituting the class (observers found this task much easier than evaluating the relative amount of unique hues in percentage). From this an ordinal scale was constructed for each chromaticity class. The chips which have the same hue scale value make up what we call isochromes. The isochromes for each chromaticity class were plotted in the SML cone space (for equi-energy illumination). As a result we have a geometrical representation of the Munsell colours used that is based on both physiological and psychological grounds.
Supported by the Wellcome Trust grant (GR068672MA)