Daylight, biochrome surfaces, and human chromatic response in the Fourier domain.

We first report Fourier analyses of a collection of 348 daylight spectral power distributions and 1,695 biochrome surface reflectance functions. The power spectra of the daylights are low pass with more than 99% of spectral power below 1 cycle/300 nm and 99.9% below 3 cycles/300 nm. The power spectra of reflectance functions are also low pass with more than 99% of spectral power below 4 cycles/300 nm and 99.9% below 11 cycles/300 nm. Consequently, the resulting color signals are typically low pass with, for our samples, an estimated frequency cutoff of 5 cycles/300 nm. Theoretical and experimental data concerning human chromatic response in the frequency domain show that this limit corresponds to the highest frequency that the color system can resolve. The implications for normal and abnormal human color vision are discussed.