WorldCat Identities

Weinshall, Daphna

Works: 24 works in 64 publications in 1 language and 449 library holdings
Genres: Conference papers and proceedings 
Roles: Author, Editor, Thesis advisor
Classifications: Q335.M41, 621.3828
Publication Timeline
Most widely held works by Daphna Weinshall
Detection and Identification of Rare Audiovisual Cues by Daphna Weinshall( )

8 editions published between 2011 and 2013 in English and held by 31 WorldCat member libraries worldwide

Stimulus familiarity determines recognition strategy for novel 3D objects by Shimon Edelman( Book )

4 editions published in 1989 in English and held by 5 WorldCat member libraries worldwide

Everyday objects are more readily recognized when seen from certain representative, or canonical, viewpoints than from other, random, viewpoints. We investigated the canonical views phenomenon for novel 3D objects. In particular, we looked for the effects of object complexity and familiarity on the variation of response times and error rates over different views of the object. Our main findings indicate that the responses times for different views become more uniform with practice, even though the subjects in our experiments received no feedback as to the correctness of their responses. In addition, the orderly dependency of the response time on the distance to a good view, characteristic of the canonical views phenomenon, disappears with practice. One possible interpretation of our results is in terms of a tradeoff between memory needed for storing specific-view representations of objects and time spent in recognizing the objects. Keywords: Visual perception; Image processing. (SDW)
Qualitative depth and shape from stereo, in agreement with psychophysical evidence by Daphna Weinshall( Book )

2 editions published in 1987 in English and held by 5 WorldCat member libraries worldwide

This paper concentrates on the problem of obtaining depth information from binocular disparities. It is motivated by the fact that implementing registration algorithms and using the results for depth computations is hard in practice with real images due to noise and quantization errors. We will show that qualitative depth information can be obtained from stero disparities with almost no computations, and with no prior knowledge(or computation)of camera parameters. The only constraint is that the epipolar plane of the fixation point includes the X-axes of both cameras. We derive two expressions that order all matched points in the images in two distinct depth-consistent fashions from image coordinates only. One is a tilt-related order lambda, which depends only on the polar angles of the matched points, the other is a depth-related order chi. Using lambda for tilt estimation and point separation(in depth)demonstrates some anomalies and unusual characteristics that have been observed in psychophysical experiments, most notably the induced size effect . Furthermore, the same approach can be applied to estimate some qualitative behavior of the normal to the surface of any object in the field of view. More specifically, one can follow changes in the curvature of contour on the surface of an object, with either x- or y-coordinate fixed. Keywords: Stero vision; Qualitative depth; Induced effect; Motion; Psychophysiology. (sdw)
Condensing image databases when retrieval is based on non-metric distances by Daphna Weinshall( Book )

3 editions published in 1997 in English and held by 5 WorldCat member libraries worldwide

Abstract: "One of the key problems in appearance-based vision is understanding how to use a set of labeled images to classify new images. Classification systems that can model human performance, or that use robust image matching methods, often make use of similarity judgments that are non-metric; but when the triangle inequality is not obeyed, most existing pattern recognition techniques are not applicable. We note that exemplar-based (or nearest-neighbor) methods can be applied naturally when using a wide class of non-metric similarity functions. The key issue, however, is to find methods for choosing good representatives of a class that accurately characterize it. We show that existing condensing techniques for finding class representatives are ill-suited to deal with non-metric dataspaces. We then focus on developing techniques for solving this problem, emphasizing two points: First, we show that the distance between two images is not a good measure of how well one image can represent another in non-metric spaces. Instead, we use the vector correlation between the distances from each image to other previously seen images. Second, we show that in non-metric spaces, boundary points are less significant for capturing the structure of a class than they are in Euclidean spaces. We suggest that atypical points may be more important in describing classes. We demonstrate the importance of these ideas to learning that generalizes from experience by improving performance using both synthetic and real images."
Dual computation of projective shape and camera positions from multiple images by Stefan Carlsson( Book )

4 editions published in 1996 in English and held by 5 WorldCat member libraries worldwide

Abstract: "Given multiple image data from a set of points in 3-D, ther are two fundamental questions that can be addressed: What is the structure of the set of points in 3-D? What are the positions of the cameras relative to the points? In this paper we show that, for projective views and with structure and position defined projectively, these problems are dual: the solutions to these problems are dual because they arise from constraint equations where space points and camera positions occur in a reciprocal way. More specifically, by using canonical reference frames for all points in space and images, the imaging of point sets in space by multiple cameras can be captured by constraint relations involving three different parameters only: (1) space points, (2) camera center points, (3) image points. The duality implies that the problem of computing camera positions from p points in n views can be solved with the same algorithm as the problem of directly reconstructing n + 4 points in p - 4 views. This unifies different approaches to projective reconstruction: methods based on external calibration and direct methods exploiting constraints that exist between shape and image invariants."
Distance metric between 3D models and 2D images for recognition and classification by Mekhon Ṿaitsman le-madaʻ( Book )

5 editions published between 1992 and 1994 in English and held by 4 WorldCat member libraries worldwide

Abstract: "Similarity measurements between 3D objects and 2D images are useful for the tasks of object recognition and classification. We distinguish between two types of similarity metrics: metrics computed in image-space (image metrics) and metrics computed in transformation-space (transformation metrics). Existing methods typically use image metrics; namely, metrics that measure the difference in the image between the observed image and the nearest view of the object. Example for such a measure is the Euclidean distance between feature points in the image and their corresponding points in the nearest view. (Computing this measure is equivalent to solving the exterior orientation calibration problem.)
The matching of doubly ambiguous stereograms by Daphna Weinshall( Book )

2 editions published in 1991 in English and held by 4 WorldCat member libraries worldwide

Algorithms that can be modified to perform consistently with human perception, and the constraints imposed on their parameters by human perception, are discussed."
Seeing ghost solutions in stereo vision by Daphna Weinshall( Book )

2 editions published in 1988 in English and held by 4 WorldCat member libraries worldwide

A unique matching is a stated objective of most computational theories of stereo vision. This report describes situations where humans perceive a small number of surfaces carried by non-unique matching of random dot patterns, although a unique solution exists and is observed unambiguously in the perception of isolated features. We find both cases where non-unique matchings compete and suppress each other and cases where they are all perceived as transparent surfaces. The circumstances under which each behavior occurs are discussed and a possible explanation is sketched. It appears that matching reduces many false targets to a few, but may still yield multiple solutions in some cases through a (possibly different) process of surface interpolation
Shape descriptors : bilinear, trilinear, and quadrilinear relations for multi-point geometry by Daphna Weinshall( Book )

3 editions published in 1995 in English and held by 4 WorldCat member libraries worldwide

Abstract: "The geometry of 1 point in N images under perspective projection has been thoroughly investigated, identifying bilinear, trilinear, and quadrilinear relations between the projections of 1 point in 2, 3 and 4 frames respectively. The dual problem -- the geometry of N points in 1 image -- has been studied mostly in the context of object recognition, often assuming weak perspective or affine projection. We provide here a complete description of this problem. We employ a formalism in which multi-frame and multi-point geometries appear in symmetry: points and projections are interchangeable. We then derive bilinear equations for 6 points (dual to 4-frame geometry), trilinear equations for 7 points (dual to 3-frame geometry), and quadrilinear equations for 8 points (dual to the epipolar geometry). We show that the quadrilinear equations are dependent on the the [sic] bilinear and trilinear equations, and that adding more points will not generate any new equation. Applications to reconstruction and recognition: The new equations are used to design new algorithms for the reconstruction of shape from many frames, and for learning invariant relations for indexing into a data-base. We describe algorithms which require matching 6 (or more) corresponding points from at least 4 images, 7 (or more) points from at least 3 images, or 8 (or more) points from at least 2 images. Unlike previous approaches, the equations developed here lead to direct and linear solutions without going through the cameras' geometry. Our final linear shape computation uses all the available data -- all points and all frames simultaneously: it uses a factorization of the matrix of invariant relations into 2 components of rank 4, a shape matrix and a coordinate-system matrix."
Complexity of indexing : efficient and learnable large database indexing by Michael Warman( Book )

3 editions published in 1995 in English and held by 4 WorldCat member libraries worldwide

Abstract: "Object recognition starts from a set of image measurements (including locations of points, lines, surfaces, color, and shading), which provides access into a database where representations of objects are stored. We describe a complexity theory of indexing, a meta- analysis which identifies the best set of measurements (up to algebraic transformations) such that: (1) the representation of objects are linear subspaces and thus easy to learn; (2) direct indexing is efficient since the linear subspaces are of minimal rank. Index complexity is determined via a simple process, equivalent to computing the rank of a matrix. We readily rederive the index complexity of the few previously analyzed cases. We then compute the best index for new and more interesting cases: 6 points in one perspective image, 6 directions in one para-perspective image, and 2 perspective images of 7 points. With color we get the following result: 4 color sensors are sufficient for color constancy at a point, and the sensor-output index is irreducible; the most efficient representation of a color is a plane in 3D space. For future applications with any vision problem where the relations between shape and image measurements can be written down, we give an automatic process to construct the most efficient database that can be directly obtained by learning from examples."
Minimal decomposition of model-based invariants, and apllications to projective reconstruction and 3D recognition by Daphna Weinshall( Book )

3 editions published in 1996 in English and held by 4 WorldCat member libraries worldwide

Abstract: "Model-based invariants are relations between model parameters and image measurements, independent of the imaging parameters. Such relations are true for all images of the model. Here we describe an algorithm which, given L independent model-based polynomial invariants describing some shape, will provide a linear re-parameterization of the invariants. This re-parameterization has the properties that: (i) it includes the minimal number of terms, and (ii) the shape terms are the same in all the model-based invariants. This final representation has 2 main applications: (1) it gives us new representations of shape in terms of hyperplanes, which are convenient for object recognition; (2) it allows the design of new linear shape from motion algorithms."
The shape of shading by Daphna Weinshall( Book )

4 editions published in 1990 in English and held by 4 WorldCat member libraries worldwide

This paper discusses the relationship between the shape of the shading, the surface whose depth at each point equals the brightness in the image, and the shape of the original surface. I suggest the shading as an initial local approximation to shape, and discuss the scope of this approximation and what it may be good for. In particular, qualitative surface features, such as the sign of the Gaussian curvature, can be computed in some cases directly from the shading. Finally, a method to compute the direction of the illuminant (assuming a single point light source) from shading on occluding contours is shown
Stability and likelihood of views of three dimensional objects by Daphna Weinshall( Book )

3 editions published in 1993 in English and held by 3 WorldCat member libraries worldwide

Abstract: "Can we say anything general about the distribution of two dimensional views of general three dimensional objects? In this paper we present a first formal analysis of the stability and likelihood of two dimensional views (under weak perspective projection) of three dimensional objects. This analysis is useful for various aspects of object recognition and database indexing. Examples are Bayesian recognition and image interpretation; indexing to a three dimensional database by invariants of two dimensional images; the selection of 'good' templates that may reduce the complexity of correspondence between images and three dimensional objects; and ambiguity resolution using generic views. We show the following results: (1) Both the stability and likelihood of views do not depend on the particular distribution of points inside the object; they both depend on only three numbers, the three second moments of the object. (2) The most stable and the most likely views are the same view, which is the 'flattest' view of the object; moreover, there is no other view which is even locally the most stable or the most likely view. Under orthographic projection, we also show: (3) the distance between one image and another does not depend on the position of its viewpoint with respect to the object, it depends only on the (geodesic) distance between the viewpoints on the viewing sphere. We demonstrate these results with real and simulated data."
Local shape approximation from shading by Daphna Weinshall( Book )

2 editions published in 1991 in English and held by 3 WorldCat member libraries worldwide

Abstract: "Shading can be used as an independent cue for exact shape recovery, or it can be used as a supplementary cue for shape interpolation between features, whose depth is known from other cues. Exact shape cannot be inferred from a local analysis of shading. However, for shape interpolation, a crude local approximation may be sufficient. This paper explores the limits of such local approximations that are easy to compute. In particular, the shape of shading is used to approximate the surface in areas of monotonic change of intensity. This analysis is complemented by a method to compute the direction of single point light source from the shading on occluding contours. A qualitative classification of shape near shading singularities is also discussed."
Three dimensional symmetry from two dimensional data by Hagit Zabrodsky( Book )

3 editions published in 1993 in English and held by 3 WorldCat member libraries worldwide

Abstract: "In previous applications, bilateral symmetry of objects was used either as a descriptive feature in domains such as recognition and grasping, or as a way to reduce the complexity of structure from motion. In this paper we propose a novel application, using the symmetry property to 'symmetrize' data before and after reconstruction. We first show how to compute the closest symmetric 2D and 3D configurations given noisy data. This gives us a symmetrization procedure, which we apply to images before reconstruction, and which we apply to the 3D configuration after reconstruction. We demonstrate a significant improvement obtained with real images. We demonstrate the relative merits of symmetrization before and after reconstruction using simulated and real data."
The evolution of sexual reproduction - a mathematical model by Daphna Weinshall( Book )

3 editions published in 1986 in English and held by 3 WorldCat member libraries worldwide

Direct computation of 3D shape and motion invariants by Daphna Weinshall( Book )

2 editions published between 1988 and 1989 in English and held by 2 WorldCat member libraries worldwide

From reference frames to reference planes : multi-view parallax geometry and applications by M Bidjan-Irani( )

1 edition published in 1998 in English and held by 1 WorldCat member library worldwide

Abnormal behavior detection in surveillance videos( Book )

1 edition published in 2012 in English and held by 1 WorldCat member library worldwide

Computational vision : a critical review by Massachusetts Institute of Technology( Book )

2 editions published in 1989 in English and held by 1 WorldCat member library worldwide

The progress made in computational vision, as represented by Marr's approach is reviewed. Outlined briefly is computational theories developed for low, middle and high vision. Then more detail solutions proposed to three representative problems in vision are discussed, each dealing with a different level of visual processing. Finally, are discussed modifications to the currently established computational paradigm that appear to be directed by the recent developments in vision
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English (60)