Color constancy in a rough world

Zaidi, Qasim

doi:10.1002/1520-6378(2001)26:1+<::aid-col41>3.0.co;2-m

Cited by 35 publications

(31 citation statements)

References 30 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…(ii) Identifying surfaces across illuminants Zaidi (1998Zaidi ( , 2001) advocates a forced-choice measure of performance colour constancy in which the observer is required to identify like surfaces across illuminants, despite obvious differences in appearance. In a typical experiment, four surfaces are presented, two under each illuminant.…”

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

confidence: 99%

Sensory, computational and cognitive components of human colour constancy

Smithson

2005

Phil. Trans. R. Soc. B

184

139

View full text Add to dashboard Cite

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.

show abstract

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

confidence: 99%

Sensory, computational and cognitive components of human colour constancy

Smithson

2005

Phil. Trans. R. Soc. B

184

139

View full text Add to dashboard Cite

show abstract

“…The primate eye is fundamentally different from the shrimp, like a digital camera it possesses a single focusing apparatus for a dense array of photoreceptors. Using just three classes of broadly tuned cone photoreceptors, the primate visual system is able to distinguish the spectra of natural lights and objects sufficiently , while maintaining good spatial resolution, and providing the means to identify objects by their colors despite variations in ambient lights and surrounding scenes (Zaidi, 1998(Zaidi, , 2001. More classes of photoreceptors would improve the sampling of natural spectra (Nascimento, Foster, & Amano, 2005), but would seriously compromise spatial resolution.…”

Section: Evolution Of Neural Computations: Mantis Shrimp and Human Comentioning

confidence: 82%

Colour vision in mantis shrimps: understanding one of the most complex visual systems in the world

Thoen¹

View full text Add to dashboard Cite

Stomatopods (commonly known as mantis shrimps) have one of the most complex visual systems in the animal kingdom with up to 20 different photoreceptor types and the ability to see both linear and circular polarized light. The eye of a stomatopod is divided into three different parts; a dorsal and a ventral hemisphere divided up by 6 distinct rows of specialised ommatidia (visual units) termed the midband. The midband contains a complex array of up to 12 spectral receptors with maximum sensitivities ranging from the ultraviolet (UV) to the far-red (300-700 nm), in addition to achromatic receptors of which several are sensitive to different forms of polarized light. The abundance of spectral receptors has puzzled researchers, as it seemed excessive even for an animal living in a spectrally rich environment such as the coral reef. Furthermore, theoretical analyses suggest that there is really no need to have more than 4-7 receptors to have satisfactory colour vision in the 300-400 nm spectral range. Our increasing knowledge of polarization sensitivity is rapidly expanding the theme of photoreceptor proliferation with up to six channels of polarization information from a combination of midband and hemisphere receptors.The aim of this thesis was to investigate how stomatopods process and analyse chromatic and polarization information using a complementary approach of behavioural, electrophysiological and neuroanatomical techniques. A comparison of spectral sensitivities across species in the superfamily Gonodactyloidea was carried out in Chapter 2. This study showed that their spectral sensitivities remain very similar between species, with narrow, steeply shaped sensitivity curves spread evenly throughout the spectrum, suggesting there is a benefit of having uniform sampling of all wavelengths. Behavioural experiments were performed to test stomatopod spectral discrimination in Chapter 3, and this was found to be surprisingly poor, both compared to other animals and to theoretical modelling. To investigate if the poor discrimination was due to the spectral shape of the stimuli, more natural-shaped stimuli (with step-shaped spectra instead of the conventional peakshaped spectra) were tested in similar experiments (Chapter 4). However, these experiments yielded similar results to the ones obtained in Chapter 3. The electrophysiological and behavioural results suggest that the stomatopod visual system may use a simpler, serial processing system unlike the "conventional" opponency system known from other animals and may be the reason for why the spectral and polarization space must be covered by several channels.While such as system may appear exceptional, there are similarities between this system and they way primates process colour, only at different steps in the processing pathway (Chapter 5). Using an interval-decoding scheme coupled with the narrow, binned spectral sensitivities of stomatopods could allow quick and precise colour judgements but at the cost of very fine discrimination. 3As very little wa...

show abstract

“…I believe we have good reasons for thinking that, in certain conditions, perceptual systems can track and reidentify on the basis of perceptual state dispositions and perspectival features without ever representing object features. For example, with respect to color perception, Zaidi (1998Zaidi ( , 2001), Foster and Nascimento (1994), and Dannemiller (1993) have suggested that we might track objects perceived at different times not by comparing their object features, but by comparing their perceptual state dispositions in light of what we can estimate about the illumination. Crudely, the idea is that we can ask whether the two perceptual state dispositions lie in the graph of transformations that correspond to ecologically realistic changes in perspectival features (here, illumination).…”

Section: What Is Represented?mentioning

confidence: 90%

“…For one thing, subjects can, when asked, make matches of perspectival features, such as ambient illumination, as opposed to object features, such as surface lightness (Katz, 1935;Gilchrist, 1988;Hurlbert, 1989;Jameson and Hurvich, 1989;Zaidi, 1998). Indeed, subjects can even characterize the different incident illumination in the two regions of a scene -say, between a swath of forest in a scene illuminated by direct sunlight and the swath of forest in the same scene illuminated by partially could-obscured sunlight (Arend, 1993;Zaidi, 2001Zaidi, , 1998. These facts give us reasonably direct reasons for believing that subjects represent perspectival features at least some of the time.…”

mentioning

confidence: 96%

Computation and the Ambiguity of Perception

Cohen¹

2012

Visual Experience

View full text Add to dashboard Cite

Sometimes towers which had looked round from a distance appeared square from close up; and enormous statues standing on their pediments did not seem large when observed from the ground.-Descartes, Meditation VI, CSM:II, 53.There is a class of phenomena that suggests strongly that perception is, in some sense to be explained, ambiguous in what it tells us about the world. In the cases at issue, the perceptual system is capable of responding to a single stimulus -say, as manifested in the ways in which subjects sort that stimulus -in different ways. Indeed, in many cases, subjects can be made to switch at will between these different modes of response. This paper is about that ambiguity, and about how it should be characterized and accounted for within a general theory of perception. The Puzzle Cases: The Ambiguity of PerceptionLet me begin, then, by bringing to mind some (I hope) familiar cases in which our perceptual systems generate multiple reactions to one stimulus. 1 (As usual in such discussions, I'll be focusing below mostly on visual perception; but I suspect that much of what I say can be generalized to at least some other perceptual modalities as well.)A first classic example is that of the non-uniformly illuminated but uniformly painted wall (e.g., as in figure 1). Consider two contiguous and samesized, same-shaped regions of the wall in figure 1 that are each (roughly) illuminated uniformly, but such that there is a difference in the illumination between the two -one is in shadow and one is in direct sunlight. Here is a fact. Subjects perceiving this stimulus condition can indicate about the differently illuminated regions (say, by their sorting behavior) that they are, in one way, alike in their color appearance and that they are, in another way, not alike in their color appearance. It seems that visual systems can pick up both the constancy/similarity or the inconstancy/dissimilarity between the regions, and subjects can respond (say, in the ways that they sort, report, or make matches) to either one. Moreover, famously, ordinary subjects can 1 be made to switch between these different modes of response simply by manipulating the task instructions (Arend and Reeves, 1986;Blackwell and Buchsbaum, 1988;Valberg and Lange-Malecki, 1990;Arend et al., 1991;Troost and deWeert, 1991;Cornelissen and Brenner, 1995;Bäuml, 1999). These familiar results give us powerful reason for believing that, in the kind of case at issue, perception is representing distinct things about the single distal stimulus. Assuming (standardly, though not uncontroversially) that perceptual states have representational contents, we can put this point by saying that the perceptual states caused by such stimuli have (at least) two different contents -one representing the aspect of similarity driving one kind of subject response, and one representing the aspect of dissimilarity driving the other kind of subject response. Here is another familiar example of the same sort of phenomenon. Viewing two telephone poles at different distances, s...

show abstract

Color constancy in a rough world

Cited by 35 publications

References 30 publications

Sensory, computational and cognitive components of human colour constancy

Sensory, computational and cognitive components of human colour constancy

Colour vision in mantis shrimps: understanding one of the most complex visual systems in the world

Computation and the Ambiguity of Perception

Contact Info

Product

Resources

About