Fourier Analysis and Color Discrimination

The contrast thresholds of equiluminous chromaticity-modulated gratings are measured for various waveforms (sine-, square-, and triangular-wave gratings). The expectation is expressed that only the fundamental Fourier component is of significance in the threshold visibility of colored gratings. In addition, the Fourier transformation is applied to the chromatic spatial-sensitivity curves. The transformed functions illustrate clearly the spatial organization of the contrast mechanisms. For 160 trolands, the summation area of the red–green chromatic activity extends over 10′, whereas the yellow–blue activity integrates over about 25′. A comparison of the Fourier transforms of a luminance- and chromatic-threshold contrast curve shows (1) inhibitory qualities and (2) the greater spatial sensitivity of the luminous function. The assumption is made that the visual resolution for differences of brightness, as well as chromaticity, is limited by the diffraction of light by the pupil. The visual acuity for differences of hue as a function of the background wavelength is thus predicted for a 30-cpd grating and compared with an empirical function. There is good agreement.