OpenRaiser/Intern-Atlas huggingface dataset:
A computational approach to boundary detection
Authors: B. S. Manjunath, Rama Chellappa
Venue: CVPR
Year: 1991

A unified approach to boundary perception is presented. The model consists of a hierarchical system which extracts and groups salient features in the image at different spatial scales. In the first stage a Gabor wavelet decomposition provides a representation of the image which is orientation selective, has optimal localization properties, and provides a good model for early feature detection. Following this, local competitive interactions are introduced which help in reducing the effects of noise and illumination variations. Scale interactions help in localizing line ends and corners, and play an important role in boundary perception. The final stage groups similar features aiding in boundary completion. Experimental results on detecting edges, texture boundaries, and illusory contours are provided.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Constrained deformable superquadrics and nonrigid motion tracking
Authors: Dimitris N. Metaxas, Demetri Terzopoulos
Venue: CVPR
Year: 1991

A physically based approach to the recovery of nonrigid 3-D motion and the tracking of nonrigid objects is presented. The approach makes use of deformable superquadrics, dynamics models that offer global deformation parameters which capture large-scale features and local deformation parameters which capture the details of complex shapes. The equations of motion governing the behavior of the models make them responsive to externally applied forces. The authors extend their prior formulation of these equations to include globally parameterized tapering and bending deformations. They further generalize the formulation to handle physically based point-to-point constraints between models. Such constraints enable one to automatically assemble object models from interconnected deformable superquadric parts. These composite models may be used to track the motions of articulated, flexible objects.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Motion analysis and epicardial deformation estimation from angiography data
Authors: Sanjoy K. Mishra, Dmitry B. Goldgof, Thomas S. Huang
Venue: CVPR
Year: 1991

A curvature-based approach to estimating nonrigid deformation of moving surfaces is described. Conformal motion can be characterized by stretching of the surface. At each point this stretching is equal in all directions, but is different for different points. This stretching function can be defined as an additional (with global translation and rotation) motion parameter. An algorithm for local stretching recovery from Gaussian curvature based on polynomial approximations of the stretching function is presented. These methods require point correspondences between time frames, but not the complete knowledge of nonrigid transformation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Camera stability problem and dynamic stereo vision
Authors: Saied Moezzi, Sandra L. Bartlett, Terry E. Weymouth
Venue: CVPR
Year: 1991

The authors show how stereo-based range data, obtained over time by a moving vehicle can be integrated without the explicit knowledge or computation of camera motion. A unique aspect of the approach is the transformation of range information into relative distances and encoding these distances in image registered maps. Results of experiments on dynamic stereo images, are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
From voxel to curvature
Authors: Olivier Monga, Nicholas Ayache, Peter T. Sander
Venue: CVPR
Year: 1991

A theoretical link is established between the 3D edge detection and the local surface approximation using uncertainty. As a practical application of the theory, a method is presented for computing typical curvature features from 3D medical images. The authors determine the uncertainties inherent in edge (and surface) detection and 2D and 3D images by quantitatively analyzing the uncertainty in edge position, orientation, and magnitude produced by the multidimensional (2D and 3D) versions of the Monga-Deriche-Canny recursive separable edge-detector. The uncertainty is shown to depend on edge orientation, e.g. the position uncertainty may vary with a ratio larger than 2.8 in the 2D case, and 3.5 in the 3D case. These uncertainties are then used to compute local geometric models (quadric surface patches) of the surface, which are suitable for reliably estimating local surface characteristics, for example, Gaussian and mean curvature. The authors demonstrate the effectiveness of these methods compared to previous techniques.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
An image pyramid with morphological operators
Authors: Aldo W. Morales, Raj Acharya
Venue: CVPR
Year: 1991

The aim of this research is to obtain a morphological pyramid with the aid of alternating sequential filters. The authors establish a relationship between alternating sequential filters and the morphological sampling theorem developed by R. Haralick et al. (1987). An alternative proof for opening and closing in the sampled and unsampled domain using the basis functions is shown. This decomposition is then used to show the relationship of the compound mapping opening-closing in the sampled and unsampled domain. An upper and a lower bound for the above relationships are presented. Under certain circumstances, an equivalence is shown for opening-closing between the sampled and the unsampled domain. An extension to more complicated algorithms using union of openings and intersection of closings is also proposed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Modeling generic polyhedral objects with constraints
Authors: Van-Duc Nguyen, Joseph L. Mundy, Deepak Kapur
Venue: CVPR
Year: 1991

A generic polyhedral model is represented as a network of nodes and constraints. Nodes are 3-D vectors representing the location and orientation of the geometric entities, or measure variables such as length or cosine. Constraints are polynomial equations in the node parameters. Modeling and recognition are viewed as solving for values of the node parameters such that all the constraint equations are satisfied and the mean square error between the model and the observed shape is minimized. Buchberger's Grobner basis algorithm and Ritt-Wu's triangulation algorithm can be used for eliminating dependent parameters as well as for detecting inconsistency among constraints. Numerical techniques are used to find the best-fit model subject to constraints.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
A multiple-baseline stereo
Authors: Masatoshi Okutomi, Takeo Kanade
Venue: CVPR
Year: 1991

A stereo matching method that uses multiple stereo pairs with various baselines generated by a lateral displacement of a camera to obtain precise distance estimates without suffering from ambiguity is presented. Matching is performed simply by computing the sum of squared-difference (SSD) values. The SSD functions for individual stereo pairs are represented with respect to the inverse distance and are then added to produce the sum of SSDs. This resulting function is called the SSSD-in-inverse-distance. It is shown that the SSSD-in-inverse-distance function exhibits a unique and clear minimum at the correct matching position, even when the underlying intensity patterns of the scene include ambiguities or repetitive patterns. The authors first define a stereo algorithm based on the SSSD-in-inverse-distance and present a mathematical analysis to show how the algorithm can remove ambiguity and increase precision. Experimental results with real stereo images are presented to demonstrate the effectiveness of the algorithm.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Shape from shading as a partially well-constrained problem
Authors: John Oliensis
Venue: CVPR
Year: 1991

For general objects, and for illumination from a general direction, the constraints on shape imposed by shading are studied. It is argued that, for a typical image, shading determines shape essentially up to a finite ambiguity. Thus regularization is often unnecessary and should be avoided. For some images, shape from shading is a partially well-constrained problem: the surface is uniquely determined over most of the image, but infinitely ambiguous in small regions bordering the image boundary, even though the image contains singular points. The main result is that, contrary to previous belief, the image of the occluding boundary does not strongly constrain the surface solution. It is shown that characteristic strips are curves of steepest ascent on the imaged surface. A theorem characterizing the properties of generic images is presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
A dynamic system for object description and correspondence
Authors: Bahram Parvin, Gérard G. Medioni
Venue: CVPR
Year: 1991

A unified framework for object description and correspondence in range images is proposed. This is based on modeling the ambiguities with a dynamic system at every level of hierarchy. The critical issue in object description is boundary completion. The authors show how this step can be modeled as the interaction of long and short term variables operating on partial contours, represented by parametric splines. In a sense, this network operates on an evolutionary basis where boundary completion is modeled as a synergistic process, and mutation is modeled as differential decay. Once reliable surface features are extracted, the same framework, with appropriate constraints, can find the corresponding surfaces and compute the transformation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Dual networks and their pattern classification properties
Authors: Ajay Patrikar
Venue: CVPR
Year: 1991

An artificial neural network (ANN) architecture termed a dual network is proposed for pattern classification problems. Dual network is a network of densely connected simple processing elements and it presents a structured way to implement polynomial classifiers. A supervised learning algorithm is developed for the dual networks, and their ability to solve complex pattern classification problems is verified through experimental studies.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Temporal slice analysis of image sequences
Authors: Shou-Ling Peng
Venue: CVPR
Year: 1991

An early-processing algorithm to extract motion information from closely sampled image sequences is presented. This method outputs dense displacement field, based on the extraction of strips in slices taken from the image volume along the temporal dimension. The extracted strips provide estimates of the velocity component along the slice orientation. Because of the high sampling rate, the motion is assumed to be piecewisely translational. A voting scheme to estimate the position of FOE while extracting strips is proposed. The true velocity can then be calculated. Results on several real image sequences and a promising speedup from the parallel implementation on the Connection Machine are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Markov/Gibbs texture modeling: aura matrices and temperature effects
Authors: Rosalind W. Picard, Ibrahim M. Elfadel, Alex Pentland
Venue: CVPR
Year: 1991

An 'aura' framework is used to rewrite the nonlinear energy function of a homogeneous anisotropic Markov/Gibbs random field (MRF) as a linear sum of aura measures. The formulation relates MRFs to co-occurrence matrices. It also provides a physical interpretation of MRF textures in terms of the mixing and separation of gray-level sets, and in terms of boundary maximization and minimization. Within this framework, the authors introduce the use of temperature for texture modeling and show how the parameters of the MRF can be interpreted as temperature annealing rates. In particular, they show evidence for a transition temperature, above which all patterns generated will be visually similar, and below which a pattern evolves down to its ground state. Results which characterize the ground state patterns are described.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Region based stereo matching oriented image processing
Authors: Sabine Randriamasy, André Gagalowicz
Venue: CVPR
Year: 1991

The authors present region-based image processing algorithms participating in task sequencing for stereo vision. The algorithms described are prior to stereo matching. Requirements in image similarity provide helpful additional knowledge for their improvement. A recursive region division algorithm using a threshold method based on contrast maximization is described. The regions are processed in parallel and absorb their noise before being thresholded. Subsequent morphological processes improve similarity and matching results. Additional knowledge is produced by analytical processes, and is useful for both segmentation and match control. Results are presented for a stereo pair of gray-level images.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Establishing motion correspondence
Authors: Krishnan Rangarajan, Mubarak Shah
Venue: CVPR
Year: 1991

A proximal uniformity constraint is proposed to solve the correspondence problem. According to this constraint, most objects in the real world follow smooth paths and cover a small distance in a small time. An efficient, noniterative polynomial time approximation algorithm which minimizes the proximal uniformity cost function and establishes correspondence over n frames is proposed. Any method using smoothness of motion alone cannot operate correctly without assuming correct initial correspondence, the correspondence in the first two frames. Therefore, the authors propose the use of gradient-based optical flow for establishing the initial correspondence. This way the proposed approach combines the qualities of the gradient- and token-based methods for motion correspondence. The algorithm is then extended to take care of restricted cases of occlusion. Experimental results for real and synthetic sequences are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
A quantitative approach to camera fixation
Authors: Daniel Raviv
Venue: CVPR
Year: 1991

The quantitative aspects of camera fixation for a static scene are addressed. In general, when the camera undergoes translation and rotation, there is an infinite number of points that produce equal optical flow for any instantaneous point in time. Using a camera-centered spherical coordinate system, it is shown how to find these points in space. For the case where the rotation axis of the camera is perpendicular to the instantaneous translation vector, these points lie on cylinders. If the elevation component of the optical flow is set to zero then these points form a circle (called the equal flow circle or simply EFC) and a line, i.e. all points that lie on this circle or line are observed as having the same azimuthal optical flow. A special case of the EFCs is the zero flow circle (ZFC) where both components of the optical flow are equal to zero. A fixation point is the intersection of all the ZFCs. Points inside and outside the ZFC can be quantitatively mapped using the EFCs. It is shown how the concept of the EFC and ZFC can be used to explain the optical flow produced by points near the fixation point.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Sequences, structure, and active vision
Authors: Raymond D. Rimey, Christopher M. Brown
Venue: CVPR
Year: 1991

Sequences of symbols generated by a visual and action sequence provide information about the natural structure of the world. HMMs (hidden Markov models) provide one way to learn (recover), store, produce, manipulate, and analyze both visual sequences and associated knowledge structures for computer vision.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Curve-based stereo: figural continuity and curvature
Authors: Luc Robert, Olivier D. Faugeras
Venue: CVPR
Year: 1991

An edge-based trinocular stereovision algorithm is presented. The primitives it works on are cubic B-spline approximations of the 2-D edges. This allows one to deal conveniently with curvature and to extend to some nonpolyhedral scenes to previous stereo algorithms. To build a matching primitive, the principle of the algorithm is, first, to find a triplet of corresponding points on three splines. This is provided by the bootstrapping part. Second, the algorithm propagates along the three supporting splines to find other matching points. This provides a set of ordered point triplets along these three splines, for which all the matching constraints are verified. This primitive constitutes a trinocular hypothesis. The set of all hypotheses is obtained by propagating from all the point triplets provided by the bootstrapping process. A criterion based on the size of the hypotheses is then used to choose among them a compatible set with respect to the uniqueness constraint. Results of several 3-D reconstructed scenes are shown.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Extracting surfaces of revolution by perceptual grouping of ellipses
Authors: Paul L. Rosin, Geoff A. W. West
Venue: CVPR
Year: 1991

Ellipses seen in an image may be the 2-D projection of 3-D circles from the scene. Given this assumption, ellipses can be grouped into perceptual groups from which inferences about the 3-D structure of objects can be made. Methods are proposed for extracting groupings corresponding to surfaces of revolution. A Hough transform approach is used for grouping, after which the confidence in the plausibility of the perceptual group is improved by detecting symmetry groupings.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Fast segmentation of range images into planar regions
Authors: Francis Schmitt 0001, Xin Chen
Venue: CVPR
Year: 1991

A split-and-merge algorithm is proposed for the segmentation of the digitized surface of a range image into planar regions. The geometric data structure used is a triangular tessellation of image domain. This data structure, combined with an adaptive surface approximation technique, allows a better adaptation of the range image segmentation to the surface boundaries. It also provides an efficient neighborhood referencing mechanism, thus resulting in a fast algorithm.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Closed-form solutions for physically-based shape modeling and recognition
Authors: Stan Sclaroff, Alex Pentland
Venue: CVPR
Year: 1991

The authors present a closed-form, physically based solution for recovering a three-dimensional (3-D) solid model from collections of 3-D surface measurements. Given a sufficient number of independent measurements, the solution is overconstrained and unique except for rotational symmetries. The proposed approach is based on the finite element method (FEM) and parametric solid modeling using implicit functions. This approach provides both the convenience of parametric modeling and the expressiveness of the physically based mesh formulation and, in addition, can provide great accuracy at physical simulation. A physically based object-recognition method that allows simple, closed-form comparisons of recovered 3-D solid models is presented. The performance of these methods is evaluated using both synthetic range data with various signal-to-noise ratios and using laser rangefinder data.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Classification of facial features for recognition
Authors: M. A. Shackleton, W. J. Welsh
Venue: CVPR
Year: 1991

A facial feature classification technique that independently captures both the geometric configuration and the image detail of a particular feature is described. The geometric configuration is first extracted by fitting a deformable template to the shape of the feature (for example, an eye) in the image. This information is then used to geometrically normalize the image in such a way that the feature in the image attains a standard shape. The normalized image of the facial feature is then classified in terms of a set of principal components previously obtained from a representative set of training images of similar features. This classification stage yields a representation vector which can be used for recognition matching of the feature in terms of image detail alone without the complication of changes in facial expression. Implementation of the system is described and results are given for its application to a set of test faces. These results show that features can be reliably recognized using the representation vectors obtained.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Unified computational theory for motion transparency and motion boundaries based on eigenenergy analysis
Authors: Masahiko Shizawa, Kenji Mase
Venue: CVPR
Year: 1991

A unified theoretical framework for motion transparency and motion boundaries by devising fundamental constraint equations of multiple optical flow is proposed. This framework can handle flow discontinuities at motion boundaries as well as flow multiplicities due to transparency of objects in a unified manner. The constraint equations are formulated by a composition of homogeneously parametrized differential operators on the space-time image. Fitting algorithms for the constraints which result in eigensystem analyses are described. To determine the number of flows, the authors use the margin energy, a measure of goodness of fit which is the difference between the first and the second lower eigenenergy of the eigensystem. They also hypothesize a criterion for multiplicity. The measure and the criterion are derived from the analogy of quantum mechanics. It is demonstrated that the margin energy can determine the transparency and discontinuities of the flow field as regions of more than one flow.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
3D from an image sequence-occlusions and perspective
Authors: Amir Shmuel, Michael Werman
Venue: CVPR
Year: 1991

The authors propose an active solution of optimally recovering 3D scene depth from a sequence of pictures. The choice of the difference between camera locations for the different pictures in the sequence is described. The tradeoff between short and long distances between successive locations of the camera is shown in terms of occlusions perspective transformation, and exact triangulation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>