Formulation of a nonlinear model of chromatic adaptation for a light-gray background

The nonlinear model of chromatic adaptation of Nayatani, Takahama, and Sobagaki^1–3 is extended to apply to an adapting field with a light-gray background. Its formulation and computational procedure are described in detail. Using the extended formulation, the following adaptation effects are predicted for a background reflectance of 50%: )1( the chromatic-adaptation effect between standard illuminants D₆₅ and A, )2( the change of colorfulness of colored samples )the Hunt effect(, )3( the change of bright and dark contrast of nonselective samples )the Stevens effect(, and )4( the color perception of nonselective samples under a colored adapting illumination )the Helson-Judd effect(. Effects )2( and )3( are observed by changing the adapting luminance. The effect of changing the background reflectance from 0.20 to 0.50 is discussed with respect to prediction of the above four effects. This change is especially significant in the Helson-Judd effect but less so in the others.