Efficient Computations and Representations of Visible Surfaces.

Richards, Whitman; Stevens, Kent A.

doi:10.21236/ada089832

Cited by 6 publications

(5 citation statements)

References 3 publications

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“…A diaphanous transparent square has both additive and multiplicative components that bias its relative depth to be in front of the other square. This can be physically realized by a finely perforated screen whose holes are below the spatial resolution limit and that transmits a fraction of the light coming from behind, and reflects a fraction coming from the front (Kersten 1991;Richards and Witkin 1979). Consistent with the interpretation of a perforated screen, a film that reduces the contrast of the edges it overlays by lightening the darker region, and darkening the lighter, without changing contrast polarity tends to be seen in front (Fig.…”

Section: Perceptual Observationsmentioning

confidence: 91%

“…Although the transparency of a surface implies that it is closer than the surface it covers, one would like to know whether transparency can provide specific depth information that could affect three-dimensional structure from motion. It turns out that particular intensity relationships not only determine whether transparency is seen (Metelli 1974;Richards and Witkin 1979;Beck et al 19841, but as is shown below, also bias which of two overlapping surfaces is seen in front. We call this depth from transparency.…”

Section: Introductionmentioning

confidence: 94%

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Interaction between Transparency and Structure from Motion

et al. 1992

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It is well known that the human visual system can reconstruct depth from simple random-dot displays given binocular disparity or motion information. This fact has lent support to the notion that stereo and structure from motion systems rely on low-level primitives derived from image intensities. In contrast, the judgment of surface transparency is often considered to be a higher-level visual process that, in addition to pictorial cues, utilizes stereo and motion information to separate the transparent from the opaque parts. We describe a new illusion and present psychophysical results that question this sequential view by showing that depth from transparency and opacity can override the bias to see rigid motion. The brain's computation of transparency may involve a two-way interaction with the computation of structure from motion.

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Section: Perceptual Observationsmentioning

confidence: 91%

Section: Introductionmentioning

confidence: 94%

Interaction between Transparency and Structure from Motion

et al. 1992

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“…Although Equation 5 Equation 6 Equation 7 were derived from an episcotister model, the same equations are also obtained from a generative model that consists of a screen (i.e., mesh) placed in front of a bipartite background. In this case, the transparent layer is modeled as a material surface containing a large number of holes that are too small to be resolved individually (Richards & Stevens, 1979). The transmittance α of the screen corresponds to the areal density of the holes, and the term t now refers to the reflectance of the material portion of the screen.…”

Section: The Episcotister Model Of Transparencymentioning

confidence: 99%

Toward a perceptual theory of transparency.

Singh¹,

Anderson²

2002

Psychological Review

166

201

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Theories of perceptual transparency have typically been developed within the context of a physical model that generates the percept of transparency (F. Metelli's episcotister model, 1974b). Here 2 fundamental questions are investigated: (a) When does the visual system initiate the percept of one surface seen through another? (b) How does it assign surface properties to a transparent layer? Results reveal systematic deviations from the predictions of Metelli's model, both for initiating image decomposition into multiple surfaces and for assigning surface attributes. Specifically, results demonstrate that the visual system uses Michelson contrast as a critical image variable to initiate percepts of transparency and to assign transmittance to transparent surfaces. Findings are discussed in relation to previous theories of transparency, lightness, brightness, and contrast-contrast.

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“…Other authors have proposed alternative schemes for the generalized description of shapes; for instance, Hoffman and Richards (1984) suggested a scheme for discovering the parts of shapes based on patterns of inflection and extremes of curvature rather than on generalized cones. Richards (1979, 1982, cited in Pinker, 1984) suggested a two-stage analysis, in which easily sensed cues for broad classes of objects (e.g., animal, vegetable, or mineral) are extracted first and are used to formulate likely hypotheses about reference frames.…”

Section: Toward a Theorymentioning

confidence: 99%

Recognition of disoriented shapes.

Corballis¹

1988

Psychological Review

238

210

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People can usually recognize a familiar shape independently of its orientation in three-dimensional space. I suggest in this article that they do this by extracting a description of the shape that is frameindependent, or independent of any coordinate system. Such a description is usually sufficient to locate the stored representation of the shape uniquely in long-term memory. However, a frameindependent description does not discriminate mirror-image shapes, which could explain the strong tendency to treat mirror images as equivalent in shape. Once a shape is identified, information about its internal axes (e.g., its top and bottom) can be recovered from memory, so that its orientation relative to the observer can be determined. The shape can then be mentally rotated to its normal or upright orientation; this normative transformation appears to be necessary if the shape is to be distinguished from its mirror image.As freely moving organisms in a world of movable objects, we are faced continually with the problem of recognizing objects or shapes in varying orientations. This is part of the more general problem of pattern recognition, whereby we recognize patterns as invariant despite the fact that they may present themselves to our senses in an infinite variety of manifestations. We may recognize a particular person, for example, whether that person is near or far, standing or sitting, in left or right profile, laughing or crying, in sunshine or in shadow.It is convenient to distinguish properties that are intrinsic to the pattern itself and that serve to define that pattern from those that depend on the particular circumstances under which the pattern is manifest to the observer. We may identify these properties as invariant and circumstantial properties, respectively.That is, we identify what things are by identifying their invariant characteristics, and we also perceive something of the circumstances surrounding them. We recognize a dog, say, but we also perceive where it is in relation to ourselves, what it is doing, and so forth.For most purposes orientation can be considered a circumstantial property. Common movable objects can appear in any orientation, yet we can usually recognize them for what they are. At the same time we can also perceive the orientations they are in. In some cases, however, it is not easy to identify patterns in unusual orientations. Rock (1973) pointed out, for instance, that it is peculiarly difficult to recognize familiar faces if they are upside down, and that it is also difficult to read cursive script upside down. These observations illustrate a further point about pattern recognition, namely, that it is hierarchical; one may still recognize an upside-down face as a face, even though

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Efficient Computations and Representations of Visible Surfaces.

Cited by 6 publications

References 3 publications

Interaction between Transparency and Structure from Motion

Interaction between Transparency and Structure from Motion

Toward a perceptual theory of transparency.

Recognition of disoriented shapes.

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