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Maximizing Rigidity: The Incremental Recovery Of 3D Structure From Rigid And . . .
 Perception
, 1983
"... The human visual system can extract 3D shape information of unfamiliar moving objects from their projected transformations. Computational studies of this capacity have established that 3D shape, can be extracted correctly from a brief presentation, provided that the moving objects are rigid. The ..."
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Cited by 76 (1 self)
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The human visual system can extract 3D shape information of unfamiliar moving objects from their projected transformations. Computational studies of this capacity have established that 3D shape, can be extracted correctly from a brief presentation, provided that the moving objects are rigid. The human visual system requires a longer temporal extension, but it can cope, however, with considerable deviations from rigidity. It is shown how the 3D structure of rigid and nonrigid objects can be recovered by maintaining an internal model of the viewed object and modifying it at each instant by the minimal nonrigid change that is sufficient to account for the observed transformation. The results of applying this incremental rigidity scheme to rigid and nonrigid objects in motion are described and compared with human perceptions.
Qualitative Depth From Stereo, With Applications
 Computer Vision, Graphics, and Image Processing
, 1990
"... Obtaining exact depth from binocular disparities is hard if camera calibration is needed. We will show that qualitative information can be obtained from stereo disparities with little computation, and without prior knowledge (or computation) of camera parameters. First, we derive two expressions tha ..."
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Cited by 16 (2 self)
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Obtaining exact depth from binocular disparities is hard if camera calibration is needed. We will show that qualitative information can be obtained from stereo disparities with little computation, and without prior knowledge (or computation) of camera parameters. First, we derive two expressions that order all matched points in the images by depth in two distinct ways from image coordinates only. Using one for tilt estimation and point separation (in depth) demonstrates some anomalies observed in psychophysical experiments, most notably the "induced size effect". We apply the same approach to detect qualitative changes in the curvature of a contour on the surface of an object, with either x or ycoordinate fixed. Second, we develop an algorithm to compute axes of zerocurvature from disparities alone. The algorithm is shown to be quite robust against violations of its basic assumptions for synthetic data with relatively large controlled deviations. It performs almost as well on real i...
Multiresolution Estimation of 2d Disparity Using a Frequency Domain Approach
, 1992
"... An efficient algorithm for the estimation of the 2d disparity between a pair of stereo images is presented. Phase based methods are extended to the case of 2d disparities and shown to correspond to computing local correlation fields. These are derived at multiple scales via the frequency domain an ..."
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Cited by 16 (9 self)
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An efficient algorithm for the estimation of the 2d disparity between a pair of stereo images is presented. Phase based methods are extended to the case of 2d disparities and shown to correspond to computing local correlation fields. These are derived at multiple scales via the frequency domain and a coarsetofine `focusing' strategy determines the final disparity estimate. Fast implementation is achieved by using a generalised form of wavelet transform, the multiresolution Fourier transform (MFT), which enables efficient calculation of the local correlations. Results from initial experiments on random noise stereo pairs containing both 1d and 2d disparities, illustrate the potential of the approach. 1 Introduction Estimating the disparity between a pair of binocular images in order to determine depth information from a scene has received considerable attention for many years. Essentially a problem of finding corresponding points in the two views of the scene, the complexity of t...
Discriminating rigid from nonrigid motion: Minimum points and views
 Perception & Psychophysics
, 1990
"... Theoretical investigations of structure from motion have demonstratedthat an ideal observer candiscriminate rigid from nonrigid motion from two views of as few as four points. We report three experiments that demonstrate similar abilities in human observers: In one experiment, 4 of 6 subjects made t ..."
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Cited by 13 (2 self)
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Theoretical investigations of structure from motion have demonstratedthat an ideal observer candiscriminate rigid from nonrigid motion from two views of as few as four points. We report three experiments that demonstrate similar abilities in human observers: In one experiment, 4 of 6 subjects made this discrimination from two views of four points; the remaining subjects required five points. Accuracy in discriminating rigid from nonrigid motion depended on the amount of nonrigidity (variance ofthe interpoint distances overviews) in the nonrigid structure. The ability to detect a rigid group dropped sharply as noise points (points not part of the rigid group) were added to the display. We conclude that human observers do extremely well in discriminating between nonrigid and fully rigid motion, but that they do quite poorly at segregating points in a display on the basis of rigidity. Human observers reportseeing threedimensional (3D) elationships in certain changing twodimensional (2D) mages—as, for example, in images that represent projecions of rotating solid objects (Wallach & O’Connell, 953) or projections of rotating patterns of dots (Brauntein,
Misperceptions of angular velocities influence the perception of rigidity in the kinetic depth effect
 Journal of Experimental Psychology: Human Perception & Performance
, 1997
"... Accuracy in discriminating rigid from nonrigid motion was investigated for orthographic projections of threedimensional rotating objects. In 3 experiments the hypothesis that magnitudes of angular velocity are misperceived in the kinetic depth effect was tested, and in 4 other experiments the hypot ..."
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Cited by 11 (7 self)
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Accuracy in discriminating rigid from nonrigid motion was investigated for orthographic projections of threedimensional rotating objects. In 3 experiments the hypothesis that magnitudes of angular velocity are misperceived in the kinetic depth effect was tested, and in 4 other experiments the hypothesis that misperceiving angular velocities leads to misperceiving rigidity was tested. The principal findings were (a) the magnitude of perceived angular velocity is derived heurisdcally as a function of a property of the firstorder optic flow called deformation and (b) perceptual performance in discriminating rigid from nonrigid motion is accurate in cases when the variability of the deformations of the individual triplets of points of the stimulus displays favors this interpretation and not accurate in other cases. The human perceptual system is capable of extracting threedimensional (3D) information from moving images from which every static pictorial cue to depth has been removed, a phenomenon called the kinetic depth effect (Wallach & O'Cormell, 1953). Numerous attempts to reach a theoretical understanding of this phenomenon have been
A Multiresolution Frequency Domain Algorithm for Fast Image Registration
 IN PROC. 3RD INT. CONF. ON VISUAL SEARCH,NOTTINGHAM
, 1992
"... An image registration algorithm based on combining phase differences at uniformly distributed spatial frequencies is described. The scheme accomodates 2d disparities and when incorporated within a coarsetoaffine analysis over scale, allows for fast registration even in the presence of large di ..."
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Cited by 4 (2 self)
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An image registration algorithm based on combining phase differences at uniformly distributed spatial frequencies is described. The scheme accomodates 2d disparities and when incorporated within a coarsetoaffine analysis over scale, allows for fast registration even in the presence of large disparities. Experiments performed on random noise stereo pairs demonstrate the potential of the approach.
Perspective Projection Invariants
, 1986
"... An important part of stereo vision consists of finding and matching points in two images which correspond to the same physical element in the scene. We show that zeros of curvature of curves are perspective projection invariants and can therefore be used to find corresponding points. They can be use ..."
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Cited by 3 (0 self)
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An important part of stereo vision consists of finding and matching points in two images which correspond to the same physical element in the scene. We show that zeros of curvature of curves are perspective projection invariants and can therefore be used to find corresponding points. They can be used to help solve the registration problem (LonguetHiggins, 1982) and to obtain the correct depth when a curve enters the forbidden zone (Krol and van de Grind, 1982). They are also relevant to theories for representing image curves. We consider the stability of these zeros of curvature.
Horizontal and vertical disparity, eye position, and stereoscopic slant perception
, 1998
"... The slant of a stereoscopically defined surface cannot be determined solely from horizontal disparities or from derived quantities such as horizontal size ratio (HSR). There are four other signals that, in combination with horizontal disparity, could in principle allow an unambiguous estimate of sla ..."
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The slant of a stereoscopically defined surface cannot be determined solely from horizontal disparities or from derived quantities such as horizontal size ratio (HSR). There are four other signals that, in combination with horizontal disparity, could in principle allow an unambiguous estimate of slant: the vergence and version of the eyes, the vertical size ratio (VSR), and the horizontal gradient of VSR. Another useful signal is provided by perspective slant cues. The determination of perceived slant can be modeled as a weighted combination of three estimates based on those signals: a perspective estimate, a stereoscopic estimate based on HSR and VSR, and a stereoscopic estimate based on HSR and sensed eye position. In a series of experiments, we examined human observers ’ use of the two stereoscopic means of estimation. Perspective cues were rendered uninformative. We found that VSR and sensed eye position are both used to interpret the measured horizontal disparities. When the two are placed in conflict, the visual system usually gives more weight to VSR. However, when VSR is made difficult to measure by using short stimuli or stimuli composed of vertical lines, the visual system relies on sensed eye position. A model in which the observer’s slant estimate is a weighted average of the slant estimate based on HSR and VSR and the one based on HSR and eye position accounted well for the data. The weights varied across viewing conditions because the informativeness of the signals they employ vary from one