Abstract

Color appearance and color constancy depend upon the chromaticity co-ordinates of light falling on the retina, not on the cornea. Many factors can change retinal chromaticity co-ordinates of a given test patch, including viewing conditions, spatial frequency of the stimulus, pupil size, and aging of the lens and other eye pathology. The visibility of white or monochromatic stimuli has long been modeled by the modulation transfer function. Dupuy¹ has described a model in which the retinal image is treated as a series of transformations of the physical image. The modulation transfer function of each ocular element is determined, then all elements are combined linearly. Similarly, a simple way to approximate the retinal chromaticity co-ordinates is to compute the contrast of the stimulus at each wavelength, with each factor contributing to a contrast reduction or filter, and with the contribution of factors combined linearly². For stimuli in maximal (laboratory) viewing conditions, of a moderate range of wavelengths, less than 10 cpd, and viewed with a pupil 2 mm or smaller and a healthy eye, there is usually an insignificant amount of contrast reduction²,³ for an "average" observer. Often these conditions are not met; this paper adds to our previous work a description of the effects of variations in macular pigment and lens densities for observers using color monitors. Determining the change in retinal chromaticity co-ordinates is important for several reasons. First, given the wide range of intra-observer differences in ocular pigmentation and scatter, as well as refractive error, it should be determined whether a given stimulus has chromaticity co-ordinates similar enough across observers to ensure similar color appearance. Second, with the widespread use of color monitors and displays, it is important to know whether information intended to appear a given color will, in fact, appear as intended for all the likely combinations of spatial parameters and adjacent colors. Third, to understand the neural factors involved in color appearance and color contrast, the retinal stimulus must first be determined.

© 1987 Optical Society of America