Sensory, computational and cognitive components of human colour constancy

Abstract

When the illumination on a scene changes, so do the visual signals elicited by that scene. In spite of these changes, the objects within a scene tend to remain constant in their apparent colour. We start this review by discussing the psychophysical procedures that have been used to quantify colour constancy. The transformation imposed on the visual signals by a change in illumination dictates what the visual system must 'undo' to achieve constancy. The problem is mathematically underdetermined, and can be solved only by exploiting regularities of the visual world. The last decade has seen a substantial increase in our knowledge of such regularities as technical advances have made it possible to make empirical measurements of large numbers of environmental scenes and illuminants. This review provides a taxonomy of models of human colour constancy based first on the assumptions they make about how the inverse transformation might be simplified, and second, on how the parameters of the inverse transformation might be set by elements of a complex scene. Candidate algorithms for human colour constancy are represented graphically and pictorially, and the availability and utility of an accurate estimate of the illuminant is discussed. Throughout this review, we consider both the information that is, in principle, available and empirical assessments of what information the visual system actually uses. In the final section we discuss where in our visual systems these computations might be implemented.

What is it like to have type-2 blindsight? Drawing inferences from residual function in type-1 blindsight

“…The visual system takes account of variations in the spectral composition of lights illuminating objects so that their perceived colour remains relatively unaffected by changes in illumination -the process of colour constancy (see e.g. Smithson, 2005). Colour constancy allows us to judge whether two objects seen under different illuminants are made of the same material.…”

We infer light in space

“…Missing from the literature is a consideration of how differential levels and chromaticities of the illumination that fills space are inferred (Mausfeld, 2003;Smithson, 2005). In this article, I propose that humans are aware not only of colored objects, but of the empty space around them being full of one or more levels and chromaticities of illumination.…”

Modelling fish colour constancy, and the implications for vision and signalling in water

“…4B, Figs 6-8) and the background is either open water or a grey surface at the same location as the object. We assume that colour constancy is provided by normalisation of receptor responses to the background (Smithson, 2005;Foster, 2011;Neumeyer et al, 2002). Fish may have additional retinal (Kamermans et al, 1998, Vanleeuwen et al, 2007) and higher-level mechanisms (Intskirveli et al, 2002;Smithson, 2005;Foster, 2011) but is it logical to start with von Kries constancy.…”

“…retinal) and high-level (e.g. cortical) mechanisms (Brainard and Freeman, 1997;Smithson, 2005;Foster, 2011), but it is logical to start with physiologically and mathematically the simplest colour constancy mechanism, namely the von Kries transformation, whereby each photoreceptor's response is normalised to the average for that receptor class across the image (Eqns 3,4; Worthey and Brill, 1986;Smithson, 2005;Foster, 2011).…”