Natural Illuminants Research Articles

Chromatic adaptation to natural and incandescent illuminants

A color CRT image display system was used to present adapting backgrounds that were spatially and temporally varied. Three observers adjusted the chromaticity of test stimuli to produce an achromatic appearance under a variety of adapting conditions. The achromatic-appearing chromaticities were used as measures of the observers' states of chromatic adaptation. The spatial configuration of the adapting background was varied to measure the spatial extent of the mechanisms responsible for chromatic adaptation. The temporal configuration of the adapting background was varied to measure the time-course of these mechanisms. The results show that chromatic adaptation is spatially localized with a time-course on the order of 10 sec. Since the mechanisms were shown to be spatially localized, the observed temporal integration across eye movements is required to allow these mechanisms to adjust to the spatially integrated scene chromaticity.

The computation of color constant descriptors in chromatic images

AbstractWe propose a method, based on finite‐dimensional linear models of reflection and illumination, which allows the transformation of chromatic images into color constant images. This proves to be useful in applications in which either there is no information on the illuminant present in the scene, or when such information is confounded by the existence of inter‐reflections between objects. The method proposed in this paper is aimed at computations taking place beyond the sensory level of vision systems, and may use inputs corrected by sensors (for adaptation). In contrast to previous work, we show that good results can be obtained using a 3‐receptor system and some knowledge about the spectral properties of natural materials and illuminants. In the method developed, an estimate of the illuminant in the scene is computed, which allow the computation of color constant descriptors of the pixel values in the image. In addition, we show a method of computing an estimate to the actual reflectances of the materials in the scence out of the computed color constant descriptors.

Improving color constancy of object colors

AbstractIn a study of improving the color constancy of object colors, the spectral reflectances of the eight CIE color‐rendering test samples (Munsell painted papers) were chosen as reference reflectance distributions. Many other distributions, more highly structured than those of the reference set, were synthesized by computer so as to be rendered by illuminant D65 at the chromaticity at which one or another of the CIE‐Munsell samples is rendered by D65. The chromaticities, at which each of the synthesized reflectances is rendered by each of 30 additional illuminants, define both dominant wavelength and chroma vector for the resulting 50,000 illuminant–sample combinations. For most natural illuminants, and for present commercial lamplights, color constancy is maximized by synthesizing each sample reflectance from three relatively narrow components, 50–60 nm at half height, peaking at wavelengths near 450 nm, 530 nm, and 610 nm.