On exponents of a nonlinear model of chromatic adaptation

Exponents to be used in a nonlinear model for chromatic adaptation by Nayatani, Takahama, and Sobagaki are discussed and determined as functions of the effective adapting levels by considering several experimental facts of color perception related to a change of adapting illuminance. The analyzed data refer to the color‐appearance attribute “colorfulness” studied by Hunt, the color appearance of a high‐reflectance sample studied by Hunt, the brightness studied by Stevens, and the chromatic adaptation effect between daylight and tungsten light studied by Breneman. By using the derived functions of the exponents it is shown that the model predicts quite well the following perceptual effects: (1) the chromatic adaptation effect between standard Illuminants D 65 and A, (2) the dependence of effect (1) on the adapting luminance, (3) the increase of colorfulness of colored samples (the first Hunt effect), (4) the increase of blueness of high‐reflectance samples (the second Hunt effect), (5) the increase of bright and dark contrast of nonselective samples (the Stevens effect), and (6) the color perception of nonselective samples under a colored adapting illumination (the Helson effect). Effects (3)–(5) are observed by increasing the adapting luminance.