An operational approach to colour constancy

Craven, Ben; Foster, David H.

doi:10.1016/0042-6989(92)90228-b

Cited by 119 publications

(103 citation statements)

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“…In other words, it follows from our data that although an illumination change results in a change in the object's lightness, the object remains close to itself (in terms of dissimilarity), a form of relative lightness constancy. This perhaps explains why, despite being generally good at distinguishing between material (reflectance) and illumination changes (Craven & Foster, 1992), observers typically have prob-…”

Section: Discussionmentioning

confidence: 99%

The proximity structure of achromatic surface colors and the impossibility of asymmetric lightness matching

Logvinenko

Maloney

2006

Perception & Psychophysics

118

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When scene lighting changes in intensity, objects that appear white tend to remain white in appearance, black objects remain black, and other achromatic surfaces stay roughly the same shades of gray. Although the intensity of light reflected from an object is proportional to both the intensity of incident light and the object's reflectivity (albedo), the resulting perceptual estimates of surface appearance depend primarily on surface albedo. Explaining how the human visual system achieves this lightness constancy is a major challenge for visual science (Brainard, 2003;Gilchrist et al., 1999;Hurlbert, 1998;Maloney, 1999).The principal method used to study lightness and lightness constancy is asymmetric matching. In an asymmetric matching task, the observer is instructed to match the lightness of two objects under different illumination by, in effect, changing the albedo of one of them. If the observer consistently chooses identical albedos under different illuminants, he or she is judged to be lightness constant.Although asymmetric matching is widely employed to study both lightness and color perception, the method has a major shortcoming. When observers finally set a match, they often report that the chosen chip is not, in fact, identical in appearance to the target, as the following comment taken from an asymmetric color matching study indicates:At this match point, however, the test and the match surfaces looked different, and the observers felt as if further adjustments of the match surface should produce a better correspondence. Yet turning any of the knobs or combinations of knobs only increased the perceptual difference. (Brainard, Brunt, & Speigle, 1997, p. 2098 In a recent article, Foster (2003) highlights this problem with color matching: Alleged color matches are not always perceptually identical. Our own observers confirm the observations of Foster and of Brainard and colleagues, but in the context of lightness matching. They report that a lightness match is not, in general, achievable when two surfaces are illuminated by different illuminants. Intuitively, a white surface in shadow often does not have the same appearance as a white surface under bright illumination, and no adjustment of the albedo of either surface can produce a perceptual match. So far as we can determine, Katz (1935, pp. 79ff) was the first to report that, when observers make a match in a lightness or color constancy experiment, there is usually a residual difference.In this article, we recast the asymmetric matching paradigm in terms of the apparent dissimilarity of surfaces under different illuminants. We asked observers not to set matches between pairs of surfaces under different illumiThis work was supported by BBSRC Grant 81/S13175, NIH/NEY Grant EY08266, and HFSP Grant RG0109/1999-B. The authors thank Deborah Ross for her assistance in conducting the experiments and Alan Gilchrist for comments on an earlier draft. The data reported here are available online at www.gcal.ac.uk/sls/Vision/research/staff/Logvinenko. html. Corresp...

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Section: Discussionmentioning

confidence: 99%

The proximity structure of achromatic surface colors and the impossibility of asymmetric lightness matching

Logvinenko

Maloney

2006

Perception & Psychophysics

118

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“…(i) Discriminating a change in illumination from a change in surface reflectance Foster and colleagues have proposed an operational approach to colour constancy in which observers are asked to discriminate between a change in illumination and a change in surface reflectance (Craven & Foster 1992;. Observers are exceedingly sensitive to such differences, and in §3b(iv) we discuss the neural signals that might support such discriminations.…”

Section: Cone Sensitivities S(λ) M(λ) L(λ)mentioning

confidence: 99%

“…It has been suggested that this signal might support operational colour constancy, i.e. the ability to distinguish between a change in illumination and a change in surface reflectance (Craven & Foster 1992; see §2c(i)). For ideal observers viewing uniformly illuminated Mondrian worlds, operational colour constancy is formally equivalent to colour constancy based on invariant colour percepts (see Foster & Nascimento 1994, Appendix 1;Foster et al 1997).…”

Section: (Iv) Coding Colour Relations By Ratiosmentioning

confidence: 99%

Sensory, computational and cognitive components of human colour constancy

Smithson

2005

Phil. Trans. R. Soc. B

184

139

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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.

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“…It is vitally important from the ecological point of view to distinguish between these (e.g., Gibson, 1979). Human observers have been found to be rather good at distinguishing between changes produced by illumination and reflectance in visual scenes (e.g., Craven & Foster, 1992;Foster et al, 2001;Foster, 2003;Kingdom, 2008).…”

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confidence: 99%

Lightness constancy and illumination discounting

Logvinenko

Tokunaga

2011

Atten Percept Psychophys

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Contrary to the implication of the term "lightness constancy", asymmetric lightness matching has never been found to be perfect unless the scene is highly articulated (i.e., contains a number of different reflectances). Also, lightness constancy has been found to vary for different observers, and an effect of instruction (lightness vs. brightness) has been reported. The elusiveness of lightness constancy presents a great challenge to visual science; we revisit these issues in the following experiment, which involved 44 observers in total. The stimuli consisted of a large sheet of black paper with a rectangular spotlight projected onto the lower half and 40 squares of various shades of grey printed on the upper half. The luminance ratio at the edge of the spotlight was 25, while that of the squares varied from 2 to 16. Three different instructions were given to observers: They were asked to find a square in the upper half that (i) looked as if it was made of the same paper as that on which the spotlight fell (lightness match), (ii) had the same luminance contrast as the spotlight edge (contrast match), or (iii) had the same brightness as the spotlight (brightness match). Observers made 10 matches of each of the three types. Great interindividual variability was found for all three types of matches. In particular, the individual Brunswik ratios were found to vary over a broad range (from .47 to .85). That is, lightness matches were found to be far from veridical. Contrast matches were also found to be inaccurate, being on average, underestimated by a factor of 3.4. Articulation was found to essentially affect not only lightness, but contrast and brightness matches as well. No difference was found between the lightness and luminance contrast matches. While the brightness matches significantly differed from the other matches, the difference was small. Furthermore, the brightness matches were found to be subject to the same interindividual variability and the same effect of articulation. This leads to the conclusion that inexperienced observers are unable to estimate both the brightness and the luminance contrast of the light reflected from real objects lit by real lights. None of our observers perceived illumination edges purely as illumination edges: A partial Gelb effect ("partial illumination discounting") always took place. The lightness inconstancy in our experiment resulted from this partial illumination discounting. We propose an account of our results based on the two-dimensionality of achromatic colour. We argue that large interindividual variations and the effect of articulation are caused by the large ambiguity of luminance ratios in the stimulus displays used in laboratory conditions.

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An operational approach to colour constancy

Cited by 119 publications

References 12 publications

The proximity structure of achromatic surface colors and the impossibility of asymmetric lightness matching

The proximity structure of achromatic surface colors and the impossibility of asymmetric lightness matching

Sensory, computational and cognitive components of human colour constancy

Lightness constancy and illumination discounting

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