Color by correlation: a simple, unifying framework for color constancy

Abstract

ÐThis paper considers the problem of illuminant estimation: how, given an image of a scene, recorded under an unknown light, we can recover an estimate of that light. Obtaining such an estimate is a central part of solving the color constancy problemÐthat is of recovering an illuminant independent representation of the reflectances in a scene. Thus, the work presented here will have applications in fields such as color-based object recognition and digital photography, where solving the color constancy problem is important. The work in this paper differs from much previous work in that, rather than attempting to recover a single estimate of the illuminant as many previous authors have done, we instead set out to recover a measure of the likelihood that each of a set of possible illuminants was the scene illuminant. We begin by determining which image colors can occur (and how these colors are distributed) under each of a set of possible lights. We discuss in the paper how, for a given camera, we can obtain this knowledge. We then correlate this information with the colors in a particular image to obtain a measure of the likelihood that each of the possible lights was the scene illuminant. Finally, we use this likelihood information to choose a single light as an estimate of the scene illuminant. Computation is expressed and performed in a generic correlation framework which we develop in this paper. We propose a new probabilistic instantiation of this correlation framework and we show that it delivers very good color constancy on both synthetic and real images. We further show that the proposed framework is rich enough to allow many existing algorithms to be expressed within it: the gray-world and gamut-mapping algorithms are presented in this framework and we also explore the relationship of these algorithms to other probabilistic and neural network approaches to color constancy.

Scene Illumination as an Indicator of Image Manipulation

“…As a result, machine learning methods have been more successful in processing arbitrary images, e.g. [4,9,10,14,28]. However, since illuminant estimation is an underconstrained problem, every method has its individual failure points.…”

Correction of Color Cast Images using Histogram Equalization of Local Area

“…Our discrete histogram is an approximation of and the transformation in Equation 2 approximates the one in Equation 4. While the discrete version won't result in exactly flat histograms, it will flatten them and in doing so enhance the contrast in the image.…”

“…Recent digital cameras have functions of exposure adjustment and a white balance correction [1][2][3][4][5]. However, exposure adjustment and white balance correction for the sunrise and sunset photos is difficult because of these photos have the brightness of the gradient.…”

A Composite Illumination Invariant Color Feature and Its Application to Partial Image Matching

“…The causes of such additional components and variations include the differences in object surface conditions and the spectral components of illuminations [2]- [4]. Modeling of perceptual color constancy also aims to achieve a similar goal [5], [6]. The photometric invariants have been used in 3D object recognition [7], correspondence, shape and motion estimation [4], and have achieved superior and robust results in comparison with the use of RGB color or grayscale.…”