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 y-coordinate fixed. Second, we develop an algorithm to compute axes of zero-curvature 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...

We are surrounded by surfaces that we perceive by visual means. Understanding the basic principles behind this perceptual process is a central theme in visual psychology, psychophysics and computational vision. In many of the computational models employed in the past, it has been assumed that a metric representation of physical space can be derived by visual means. Psychophysical experiments, as well as computational considerations, can convince us that the perception of space and shape has a much more complicated nature, and that only a distorted version of actual, physical space can be computed. This paper develops a computational geometric model that explains why such distortion might take place. The basic idea is that, both in stereo and motion, we perceive the world from multiple views. Given the rigid transformation between the views and the properties of the image correspondence, the depth of the scene can be obtained. Even a slight error in the rigid transformation parameters c...

between images presented to the two eyes induce a strong sensation of depth. More recent experiments with random-dot stereograms have shown that disparity is a sufficient cue for stereopsis (Julesz 1960, 1971). Disparity-tuned neurons in visual cortex were first demonstrated in the cat (Barlow et al. 1967; Nikara

We examined the influence of context on exocentric pointing. In a virtual three-dimensional set-up, we asked our subjects to aim a pointer toward a target in two conditions: The target and the pointer were visible alone, or they were visible with planes through each of them. The planes consisted of a regular grid of horizontal and vertical lines. The presence of the planes had a significant influence on the indicated direction. These changes in indicated direction depended systematically on the orientation of the planes relative to the subject and on the angle between the planes. When the orientation of the (perpendicular) planes varied from asymmetrical to symmetrical to the frontoparallel plane, the indicated direction varied over a range of 15º—from a slightly larger slant to a smaller slant—as compared with the condition without the contextual planes. When the dihedral angle between the two planes varied from 90º to 40º, the indicated direction varied over a range of less than 5º: A smaller angle led to a slightly larger slant. The standard deviations in the indicated directions (about 3º) did not change systematically. The additional structure provided by the planes did not lead to more consistent pointing. The systematic changes in the indicated direction contradict all theories that assume that the perceived distance between any two given points is independent of whatever else is present in the visual field—that is, they contradict all theories of visual space that assume that its geometry is independent

Abstract-Earlier experiments suggest that the perception of relative and absolute distance in binocular space is affected by the convergence angle to the stimulus. The question is how? A hypothesis was proposed in which the obtained effects are accounted for in terms of convergence differences. The hypothesis states that binocular stimuli are related to the rest convergence of the eyes which is assumed to be stable. Two experiments were conducted in which distance estimations were made to single binocular dots. viewed through a polarization stereoscope. The experimental results support the proposed hypothesis. Ever since Berkeley (1709), the roie of convergence in binocular space perception has been much discussed. Experimental results do not support the hypothesis that veridical perception of distances is based on convergence, but neither do they support the opposite hypothesis, i.e. that no relation exists betweenconvergence and perceived distance. The present article- is an attempt to explain the experimental results