Dr. Clifton M. Schor Profile

Dr. Clifton M. Schor

at Univ of California Berkeley

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Publications (3)

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Proceedings Article | 18 March 2005 Paper

Spatio-temporal interactions that promote the smoothness constraint for binocular matches

Clifton Schor, Zhi-Lei Zhang

Proceedings Volume 5666, (2005) https://doi.org/10.1117/12.602941

KEYWORDS: Picosecond phenomena, Stereo holograms, Visualization, Eye, Spatial frequencies, Chemical elements, Electronic imaging, Spatial analysis, Switches, Solids

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Early in his career, Bela Julesz introduced the stereo matching problem while working at Bell Labs on an encryption project. The common belief at that time was based on Wheatstone’s proposal that 2-D space perception of form preceded coding of disparity for 3-D space perception. However, with the random-dot stereogram, Julesz demonstrated that stereoscopic depth could be perceived in the absence of any identifiable objects or perspective cues available to either eye alone. This work inspired many algorithms for binocular matching including the smoothness constraint. Wheatstone’s and Julesz’s proposals as to whether binocular matches are solved at a low level, prior to form perception, or after form is perceived are still debated. We have examined spatio-temporal interactions that promote binocular matches and yield percepts of smooth surfaces in depth. We identified low-level processes for estimating depth differences between surface patches that require their proximity in both time and space, and a high level process that minimizes their depth differences when surface texture of adjacent patches appears to belong to the same surface. This suggests that the stereo-matching solution is influenced by a priori assumptions about the surface configuration of the scene and by monocular and binocular spatial cues.

Proceedings Article | 17 March 1994 Paper

Disparity tuning of cyclopean visual mechanisms

Scott Stevenson, Clifton Schor, Lawrence Cormack

Proceedings Volume 2054, (1994) https://doi.org/10.1117/12.171145

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Tuned mechanisms or `channels' have been demonstrated in many aspects of human vision, and their characteristics span a continuum from a small set of broadly tuned channels (as in the spectral tuning of cone mechanisms) to a large array of narrow channels (as in the spatial tuning of cone mechanisms). The optimal number and tuning widths of channels for a given dimension depends on a trade-off between an economy of processor resources and the avoidance of metamerism. A small number of broad channels requires a small investment in processor resources and can support fine discriminations but is subject to metameric confusions. A large number of narrow channels requires a greater investment in processor resources but allows for the representation of multiple values on the tuning dimension (e.g., transparency). In the context of stereopsis and vergence control, single unit recordings have provided evidence that disparity tuned mechanisms cover the range from closely spaced, narrow channels (`tuned' cells) to widely spaced, broad channels (`near/far' cells). In principal, near/far mechanisms should be sufficient to control vergence and allow for fine stereoacuity right around the horopter. Tuned mechanisms might be required for fine disparity discriminations off the horopter and for the perception of stereo transparency. We have investigated the disparity tuning characteristics of binocular visual mechanisms which mediate (1) the psychophysical detection of surfaces in dynamic noise stimuli and (2) the involuntary oculomotor vergence responses to such surfaces. We have found evidence that both perceptual and oculomotor systems involve a large set of narrowly tuned mechanisms with inhibition between neighboring channels. A model is developed which clarifies the nonobvious relationship between measured tuning functions and characteristics of underlying channels.

Proceedings Article | 30 June 1992 Paper

Spatiotemporal limitations on vernier and stereoscopic alignment acuity

Christopher Tyler, Clifton Schor, Nancy Coletta

Proceedings Volume 1669, (1992) https://doi.org/10.1117/12.60420

KEYWORDS: Spatial frequencies, Stereoscopic displays, Eye, Visualization, Modulation, Target detection, Data processing, Image fusion, Chlorine, CRTs

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Stereoscopic and monocular alignment acuity were measured using sinusoidal displacements in time, space, and disparity of a single line stimulus. The stereoscopic detectability was not limited by the sensitivity for the monocular components of the spatio-temporal stereo- alignment target. In fact, the two tasks seemed to be controlled by largely independent processes. Monocular sensitivity was best at high spatial perturbation frequencies, almost independent of temporal frequency, while stereoscopic sensitivity was best at low temporal and medium spatial frequencies, and its surface had a substantially different morphology. Under these dynamic conditions the lowest thresholds of either kind were of the order of 10 arc sec, setting stringent limitations on the accuracy of stereoscopic displays. The spatio- temporal surfaces we measured show regions where sensitivity is reduced by an order of magnitude, suggesting modes in which dynamic human stereopsis is more tolerant of perturbations than suggested by classical data.

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