Showing papers on "Color constancy published in 1986"

Color constancy: a method for recovering surface spectral reflectance

Abstract: Human and machine visual sensing is enhanced when surface properties of objects in scenes, including color, can be reliably estimated despite changes in the ambient lighting conditions. We describe a computational method for estimating surface spectral reflectance when the spectral power distribution of the ambient light is not known.

Evaluation of linear models of surface spectral reflectance with small numbers of parameters

Abstract: Recent computational models of color vision demonstrate that it is possible to achieve exact color constancy over a limited range of lights and surfaces described by linear models. The success of these computational models hinges on whether any sizable range of surface spectral reflectances can be described by a linear model with about three parameters. In the first part of this paper, I analyze two large sets of empirical surface spectral reflectances and examine three conjectures concerning constraints on surface reflectance: that empirical surface reflectances fall within a linear model with a small number of parameters, that empirical surface reflectances fall within a linear model composed of band-limited functions with a small number of parameters, and that the shape of the spectral-sensitivity curves of human vision enhance the fit between empirical surface reflectances and a linear model. I conclude that the first and second conjectures hold for the two sets of spectral reflectances analyzed but that the number of parameters required to model the spectral reflectances is five to seven, not three. A reanalysis of the empirical data that takes human visual sensitivity into account gives more promising results. The linear models derived provide excellent fits to the data with as few as three or four parameters, confirming the third conjecture. The results suggest that constraints on possible surface-reflectance functions and the "filtering" properties of the shapes of the spectral-sensitivity curves of photoreceptors can both contribute to color constancy. In the last part of the paper I derive the relation between the number of photoreceptor classes present in vision and the "filtering" properties of each class. The results of this analysis reverse a conclusion reached by Barlow: the "filtering" properties of human photoreceptors are consistent with a trichromatic visual system that is color constant.

Analysis of the retinex theory of color vision.

Abstract: If color appearance is to be a useful feature in identifying an object, then color appearance must remain roughly constant when the object is viewed in different contexts. People maintain approximate color constancy despite variation in the color of nearby objects and despite variation in the spectral power distribution of the ambient light. Land's retinex algorithm is a model of human color constancy. We analyze the retinex algorithm and discuss its general properties. We show that the algorithm is too sensitive to changes in the color of nearby objects to serve as an adequate model of human color constancy.

Simultaneous color constancy.

Abstract: Observers matched patches (simulated Munsell papers) in two simultaneously presented computer-controlled displays, a standard array presented under 6500-K illumination and a test array under 4000 or 10,000 K. Adaptation to the test illuminants was limited. The adjusted patch was surrounded by a single color (annulus display) or by many colors (Mondrian display). Observers either matched hue and saturation or made surface-color (paper) matches in which the subject was asked to make the test patch look as if it were cut from the same piece of paper as the standard patch. For two of the three subjects, the paper matches were approximately color constant. The hue-saturation matches showed little color constancy. Moreover, the illumination difference between the two displays was always visible. Our data show that simultaneous mechanisms alone (e.g., simultaneous color contrast) alter hues and saturations too little to produce hue constancy.

Mechanisms of color constancy.

Abstract: We develop a model of how the visual system finds the colors of objects that have unknown shapes and positions. The model relies on mechanisms of light adaptation, coupled with eye movements, to recover three descriptors of surface reflectance that are represented in the signals of an achromatic mechanism and two color-opponent mechanisms. These descriptors are transformed to yield estimates of hue, the dimension of surface color that is independent of object shape and viewing geometry.

Method for computing the scene-illuminant chromaticity from specular highlights

Abstract: The perception of an unchanging surface color under different illuminations requires the computation of the scene-illuminant color either directly or indirectly. A possible source for the computation is the specular highlight of the surface reflection. Some issues related to color constancy are discussed, and a theory for computing the scene-illuminant chromaticity from specular highlight is described. An interesting result of the theory is that in an ideal situation, two surfaces of different colors will be sufficient for the computation.

Formal connections between lightness algorithms.

Abstract: The computational problem underlying color vision is to recover the invariant surface-spectral-reflectance properties of an object. Lightness algorithms, which recover an approximation to surface reflectance in independent wavelength channels, have been proposed as one method to compute color. This paper clarifies and formalizes the lightness problem by proposing a new formulation of the intensity equation on which lightness algorithms are based and by identifying and discussing two basic subproblems of lightness and color computation: spatial decomposition and spectral normalization of the intensity signal. Several lightness algorithms are reviewed, and a new extension (the multiple-scales algorithm) of one of them is proposed. The main computational result is that each of the lightness algorithms may be derived from a single mathematical formula, under different conditions, which, in turn, imply limitations for the implementation of lightness algorithms by man or machine. In particular, the algorithms share certain limitations on their implementation that follow from the physical constraints imposed on the statement of the problem and the boundary conditions applied in its solution.

Heuristic analysis of von Kries color constancy.

Abstract: The properties of constancy models based on the proportionality rule of von Kries are examined in a series of simplified examples. It is found that the breadth of receptor-sensitivity functions causes metamerism, thwarting color constancy. Overlap of these functions limits the accuracy of von Kries adaptation for a more subtle reason: it causes nonzero off-diagonal elements in the transformation matrix relating object reflectance to receptor stimulations. Such off-diagonal elements make von Kries adaptation an inexact color-constancy scheme, even when the illuminant is restricted to prevent metamerism.

Chromatic adaptation and color constancy: A possible dichotomy

Abstract: Differences between chromatic adaptation and color constancy are discussed, in order to call into question the commonly held view that chromatic adaptation is the mechanism of color constancy. Whereas chromatic adaptation requires many seconds of time and occurs for simple visual scenes, color constancy asserts itself immediately and is most powerful in complex visual scenes. Furthermore, models of chromatic adaptation are not so illuminant invariant as other models of color vision. Therefore, a new operational foundation for color constancy is proposed, and existing non-adaptation models of color constancy are enumerated for future tests.

Central and Peripheral Mechanisms of Colour Vision

Abstract: This volume samples the proceedings of a 1984 symposium at the Wenner-Gren Center, Stockholm. The organizers of the meeting achieved in part their goal to explore "how the known physiology of the visual pathways, from the retina to central areas of the visual cortex, can account for [the perception of color]." A majority of the entries deal with the riddle of color constancy. More specifically, how is it that the color reflected from an object is perceived as unchanging despite wide variations of the intensity or color composition of light illuminating the object? Accordingly, the volume is led off by Land's presentation of the Retinex theory and an introduction to the problem of color constancy. With the exception of Zeki's consideration of the anatomy and functional organization of the monkey cortex, the remainder of the entries are by theorists and psychophysicists (Blake, Hurvich, Jameson, MacLeod, Pugh, and others) and biophysicists

Improving color constancy of object colors

Abstract: In 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.

A FORTRAN program for predicting the effects of chromatic adaptation on color appearance based on current CIE recommendations

Abstract: The CIE has recently recommended for field trial a method for predicting corresponding colors with a change in chromatic adaptation. To aid the CIE in collecting results illustrating the accuracy of these predictions, a FORTRAN program currently used by the Munsell Color Science Laboratory is listed along with test data. This chromatic-adaptation transform can be used to calculate CIELAB or CIELUV metrics for non-daylight illuminants, indices of illuminant metamerism, and indices of color constancy. Including this transform in these calculations, it is hoped, will result in metrics with better correlation to visual assessments. It is hoped that readers will implement this method, compare the effectivness of this chromatic-adaptation transform to visual evaluations, and report their results to CIE Technical Committee 1–06.