Beyond the locus of spectrally pure colors

Abstract

The spectrum locus of a CIE chromaticity diagram defines the boundary within which all physically realizable color stimuli must fall. While that is a physical and mathematical reality that cannot be violated, it is possible to create colors that appear as if they were produced by physically impossible stimuli. This can be accomplished through careful control of the viewing conditions and states of adaptation. This paper highlights the importance of considering color appearance issues in the design of displays and specification of color gamuts and illustrates how the perceived color gamut can be manipulated significantly through the relationship between white-point and primary luminance levels without changing the chromaticity gamut of a display system. Using a color appearance model, such as CIECAM02, display color gamuts can be specified in perceptual terms such as lightness, chroma, brightness, and colorfulness rather than in strictly physical terms of the stimuli that create these perceptions. Examination of these perceptual gamuts, and their relationships to the viewing conditions, allows demonstration of the possibility of producing display gamuts that appear to reach beyond the locus of pure spectral colors when compared with typical display setups.