By use of the haploscopic color-matching method, the colors induced by chromatic surrounds into an achromatic central field of a constant lower luminance (10 mL) have been measured. For inducing colors of constant chromaticity, an increasing luminance yielded induced colors of lower lightness but of constant chromaticity. For 21 dominant and complementary wavelengths of the inducing stimuli, the induced colors have been measured as functions of the purity of the surround. The results can be described within an opponent color metric by means of simple simultaneous power equations in the partial and resultant opponent purities, with wavelength-dependent exponents and constants, and one linear equation for the luminance ratio. For a unit change of purity of the inducing color, the exponents of the power functions represent a measure of the strength of induction. The values of the exponents and the constants have been tabulated and plotted against wavelength. By interpolation in these curves, it is possible to predict the equivalent color-matching coordinates of an induced color, for any combination of dominant wavelength and purity of the inducing color stimulus. A quantitative formulation of color induction that also incorporates the dependence on (a) the photopic light adaptation level, (b) the angular size of the annular inducing stimulus, and (c) the time of fixation of the test field, is suggested.
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