We introduce virtual snakes for generating occlusion hypotheses. Initially, snakes are clustered based on their motion to form object hypotheses-a type of motion segmentation. When two snakes intersect, four virtual s...
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We introduce virtual snakes for generating occlusion hypotheses. Initially, snakes are clustered based on their motion to form object hypotheses-a type of motion segmentation. When two snakes intersect, four virtual snakes are generated-a background and a foreground snake for each of the original two. The two foreground virtual snakes are allowed to relax, while the two background virtual snakes move in accordance with their previous motion. The combined energies of the snakes in the two colliding objects are examined after the collision to determine the occlusion relationship, and the inconsistent virtual snakes are deleted. We show that this heuristic can be used to correctly track objects in the presence of strong occlusion.
This paper introduces a new framework for stereo correspondence recovery using one motion of a stereo rig. Both the stereo correspondence and the motion of the stereo rig are unknown. By combining the stereo geometry ...
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This paper introduces a new framework for stereo correspondence recovery using one motion of a stereo rig. Both the stereo correspondence and the motion of the stereo rig are unknown. By combining the stereo geometry and the motion correspondence we are able to infer the stereo correspondence from motion correspondence without having to systematically use the intensity-based stereo matching algorithms. The stereo correspondence recovery consists of two consecutive steps: the first step uses metric data associated with the stereo rig while the second step uses feature correspondences only. Experiments involving real stereo pairs indicate the feasibility and robustness of the approach.
We present a novel algorithm performing projective rectification which does not require explicit computation of the epipolar geometry and specifically of the fundamental matrix. Instead of finding the epipoles and com...
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We present a novel algorithm performing projective rectification which does not require explicit computation of the epipolar geometry and specifically of the fundamental matrix. Instead of finding the epipoles and computing two homographies mapping the epipoles to infinity, as done in recent work on projective rectification, we exploit the fact that the fundamental matrix of a pair of rectified images has a particular, known form. This allows us to set up a minimization that yields the rectifying, homographies directly from image correspondences. Experimental results show that our method works quite robustly even in the presence of noise, and with inaccurate point correspondences. The code of our implementation will be made available at the author's web site.
By using mirror reflections of a scene, stereo images can be captured with a single camera (catadioptric stereo). Single camera stereo provides both geometric and radiometric advantages over traditional two camera ste...
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By using mirror reflections of a scene, stereo images can be captured with a single camera (catadioptric stereo). Single camera stereo provides both geometric and radiometric advantages over traditional two camera stereo. In this paper we discuss the geometry and calibration of catadioptric stereo with two planar mirrors and show how the relative orientation, the epipolar geometry and the estimation of the focal length are constrained by planar motion. In addition, we have implemented a real-time system which demonstrates the viability of stereo with mirrors as an alternative to traditional two camera stereo.
This paper proposes a method for obtaining surface orientations of transparent objects using polarization in highlight. Since the highlight, the specular component of reflection light from objects, is observed only ne...
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This paper proposes a method for obtaining surface orientations of transparent objects using polarization in highlight. Since the highlight, the specular component of reflection light from objects, is observed only near the specular direction, it appears merely on limited parts on an object surface. In order to obtain orientations of a whole object surface, we employ a spherical extended light source. This paper reports its experimental apparatus, a shape recovery algorithm, and its performance evaluation.
We present a quantitative evaluation of an algorithm for model-based face recognition. The algorithm actively learns how individual faces vary through video sequences, providing on-line suppression of confounding fact...
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We present a quantitative evaluation of an algorithm for model-based face recognition. The algorithm actively learns how individual faces vary through video sequences, providing on-line suppression of confounding factors such as expression, lighting and pose. By actively decoupling sources of image variation, the algorithm provides a framework in which identity evidence can be integrated over a sequence. We demonstrate that face recognition can be considerably improved by the analysis of video sequences. The method presented is widely applicable in many multi-class interpretation problems.
Large calibrated datasets of 'random' natural images have recently become available. These make possible precise and intensive statistical studies of the local nature of images. We report results ranging from ...
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Large calibrated datasets of 'random' natural images have recently become available. These make possible precise and intensive statistical studies of the local nature of images. We report results ranging from the simplest single pixel intensity to joint distribution of 3 Haar wavelet responses. Some of these statistics shed light on old issues such as the near scale-invariance of image statistics and some are entirely new. We fit mathematical models to some of the statistics and explain others in terms of local image features.
Facial variation divides into a number of functional subspaces. An improved method of measuring these was designed within the space defined by an Appearance Model. Initial estimates of the subspaces (lighting, pose, i...
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Facial variation divides into a number of functional subspaces. An improved method of measuring these was designed within the space defined by an Appearance Model. Initial estimates of the subspaces (lighting, pose, identity, expression) were obtained by Principal Components Analysis on appropriate groups of faces. An iterative algorithm was applied to image codings to maximise the probability of coding across these non-orthogonal subspaces before obtaining the projection on each sub-space and recalculating the spaces. This procedure enhances identity recognition, reduces overall sub-space variance and produces Principal Components with greater span and less contamination.
This paper addresses the problem of probabilistic recognition of activities from local spatio-temporal appearance. Joint statistics of space-time filters are employed to define histograms which characterize the activi...
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This paper addresses the problem of probabilistic recognition of activities from local spatio-temporal appearance. Joint statistics of space-time filters are employed to define histograms which characterize the activities to be recognized. These histograms provide the joint probability density functions required for recognition using Bayes rule. The result is a technique for recognition of activities which is robust to partial occlusions as well as changes in illumination. In this paper the framework and background for this approach is first described. Then the family of spatio-temporal receptive fields used for characterizing activities is presented. This is followed by a review of probabilistic recognition of patterns from joint statistics of receptive field responses. The approach is validated with the results of experiments in the discrimination of persons walking in different directions, and the recognition of a simple set of hand gestures in an augmented reality scenario.
Wide-Angle lenses are not often used for 3D reconstruction tasks, in spite of the potential advantages offered by their increased field-of-view, because (1) existing algorithms for high-distortion lens compensation pe...
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Wide-Angle lenses are not often used for 3D reconstruction tasks, in spite of the potential advantages offered by their increased field-of-view, because (1) existing algorithms for high-distortion lens compensation perform poorly at image extremities and (2) procedures for the reconstruction of recti-linear images place a large burden on system resources. In this paper, a projection model based on quadric surfaces is presented which accurately characterizes the effect of wide-angle lenses across the entire image and allows for the use of novel feature matching strategies that do not require nonlinear distortion compensation.
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