OpenRaiser/Intern-Atlas huggingface dataset:
A linear algorithm for computing the phase portraits of oriented textures
Authors: Chiao-Fe Shu, Ramesh C. Jain, Francis K. H. Quek
Venue: CVPR
Year: 1991

Phase portraits are a powerful mathematical model for describing oriented textures. An isotangent-based approach is presented which is a linear formulation to the problem, to locate the critical points and compute the parameter sets of this model for the nonsingular two-dimensional first-order phase portraits. The authors classify flow patterns by Jordan canonical forms of the characteristic matrix made up of the estimated parameters. For these systems, they prove that all the isotangent curves are straight lines which intersect at a critical point. They also apply least median of squares (LMS) estimators to find the isotangent lines and locate the critical point. A linear regression technique is used to estimate the parameters of the two-dimensional first-order phase portrait of a given flow pattern. Results of applying the algorithm to synthetic and real images are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Surface approximation using weighted splines
Authors: Sarvajit S. Sinha, Brian G. Schunck
Venue: CVPR
Year: 1991

The surface reconstruction problem is formulated as a two-stage reconstruction procedure. The first stage is a robust local fit to the data in a multiresolution scheme and the second is a regularized least squares fit, with the addition of an adaptive mechanism in the smoothness functional in order to make the solution well behaved. The authors present the details of the second stage in which they use the weighted bicubic spline as a surface representation in a regularization framework, with a Tikhonov stabilizer, as the smoothness norm. It is shown how the adaptive weights, in the stabilizer help the surface bend across discontinuities by varying the energy of the surface.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Generic recognition through qualitative reasoning about 3-D shape and object function
Authors: Louise Stark, Kevin W. Bowyer
Venue: CVPR
Year: 1991

The work which demonstrates the feasibility of a different approach to 3-D object recognition is described. The authors construct a definition of a generic object category, such as a chair, in terms of the function required of the object. This definition is based on qualitative reasoning about 3-D shape, and does not imply any particular geometric or structural model for an object. Thus, this approach has the potential to lead to recognition systems of much greater generality than current CAD-based or model-based approaches.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Structural hashing: efficient three dimensional object recognition
Authors: Fridtjof Stein, Gérard G. Medioni
Venue: CVPR
Year: 1991

An approach for the recognition of multiple three-dimensional object models from three-dimensional scene data is presented. The authors work on dense data, but neither the models nor the scene data have to be complete. The problem is addressed in a realistic environment: the viewpoint is arbitrary, the objects vary widely in complexity, and no assumptions about the structure of the surface are made. The approach is novel in that it uses two different types of primitives for matching: small surface patches, where differential properties can be reliably computed, and lines corresponding to depth or orientation discontinuities. These are represented by splashes and 3-D curves respectively. It is shown how both of these primitives can be encoded by a set of super segments, consisting of connected linear segments. These super segments are entered into a hash table, and provide the essential mechanism for fast retrieval and matching.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
An analysis of the probability of disparity changes in stereo matching and a new algorithm based on the analysis
Authors: Charles V. Stewart
Venue: CVPR
Year: 1991

The main contributions of this research are: (1) the derivation of the probability density function (pdf) of disparity changes in stereo matching based on the pdf of depth changes in the world and on the parameters of the stereo image formation process, (2) the definition of a match support equation based on the derived pdf, and (3) the incorporation of the support equation into a relaxation matching algorithm. The derived pdf and support equation are applicable to many existing stereo algorithms.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Integration and interpretation of incomplete stereo scene data
Authors: Kazuhide Sugimoto, Hironobu Takahashi, Fumiaki Tomita
Venue: CVPR
Year: 1991

The authors extend the algorithm for stereo vision on a mobile robot in a unstructured environment to generate the 3-D b-rep of the large environment by incrementally integrating local and incomplete stereo data. The stereo vision is based on the 2-D b-reps of stereo images. The 2-D b-rep is a 2-D version of the 3-D b-rep to describe an image; the image is represented in a hierarchy of regions, boundaries, and line-segments. The b-rep is obtained for each of stereo images and the two images are matched on this data structure. The direct output of stereo is 3-D wireframes, a set of 3-D loops (boundaries) composed of 3-D line-segments, of the scene. A unique surface is then defined for each loop to make the 3-D b-rep, the consistent geometrical model, of the scene. It is necessary for the mobile robot to change views of the scene to make uninterpretable loops interpretable by finding missing segments, and thus make the complete b-rep of the scene.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Estimation of motion and structure of planar surfaces from a sequence of monocular images
Authors: Sanghoon Sull, Narendra Ahuja
Venue: CVPR
Year: 1991

An algorithm is presented which estimates 10 parameters for motion and structure of a rigid planar patch given point correspondences in a monocular image sequence under perspective projection. The rotational velocity is assumed constant and the rotation center arbitrary. The algorithm mainly consists of two steps. First, the 3-D space of ( omega /sub x/, omega /sub y/, omega /sub z/) is searched exhaustively and for each ( omega /sub x/, omega /sub y/, omega /sub z/) all the other parameters with the value of an objective function are computed linearly. some of the ( omega /sub x/, omega /sub y/, omega /sub z/) and the corresponding structure values are used as the initial guesses in the second step. The objective function is iteratively minimized with respect to five variables for rotation and structure. The solution corresponding to the global minimum is used to obtain least squares estimates of the remaining unknowns, for translation and rotation center. It was experimentally found that the objective function converges well so that the 3-D space need not be densely searched. Results are presented for three image sequences, two simulated and one real.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Robust vectorization using graph-based thinning and reliability-based line approximation
Authors: Satoshi Suzuki, Naonori Ueda
Venue: CVPR
Year: 1991

A vectorization method for line patterns which converts digital binary images into line-segment vectors is proposed. The proposed method suppresses shape distortion as well as pseudo-feature points, so it produces more compact and natural-shaped vector data than existing methods. The experimental results of applying the proposed method to geographical maps show that the vectorization method reduces data volume by 74%-87% and suppresses shape distortion more than is possible with a straightforward method.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Partial implementation of the fixation method on real images: direct recovery of motion and shape in the general case
Authors: M. Ali Taalebinezhaad
Venue: CVPR
Year: 1991

A direct method called fixation is introduced for solving the general motion vision problem, arbitrary motion relative to an arbitrary rigid scene. This method results in a linear constraint equation which explicitly expresses rotational velocity in terms of translational velocity. By combining this constraint equation with the brightness-change constraint equation, general solutions are found for translational and rotational velocities, and the shape. Avoiding correspondence and optical flow has been the motivation behind this direct method, which uses the brightness gradients directly. Partial implementation of the fixation method on real images has shown encouraging results which support some of the presented algorithms.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Positional estimation of a mobile robot using edge visibility regions
Authors: Raj Talluri, Jake K. Aggarwal
Venue: CVPR
Year: 1991

A technique is presented for estimating the position and pose of an autonomous mobile robot navigating in an outdoor, urban environment consisting of polyhedral buildings. The 3-D description of the roof tops of the buildings are assumed to be given as a world model. A discussion is presented of the uses of an intermediate representation of the environment, called the edge visibility regions (EVRs), in the positional estimation process.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Computing viewpoints that satisfy optical constraints
Authors: Konstantinos A. Tarabanis, Roger Y. Tsai
Venue: CVPR
Year: 1991

The authors present techniques with which camera viewpoints can be automatically determined in order to satisfy the generic feature detectability requirements of resolution, focus, and field-of-view. These optical constraints are characterized analytically for a general thick lens model, and complete viewpoint loci that satisfy these constraints are obtained. The results discussed are useful for automating the vision system design process, as well as for programming the vision system itself. In addition, such planning techniques can also automate robot imaging systems that reconfigure themselves in an intelligent manner in order to optimize imaging quality.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Sampling and reconstruction with adaptive meshes
Authors: Demetri Terzopoulos, Manuela Vasilescu
Venue: CVPR
Year: 1991

An approach to visual sampling and reconstruction motivated by concepts from numerical grid generation is presented. Adaptive meshes that can nonuniformly sample and reconstruct intensity and range data are presented. These meshes are dynamic models which are assembled by interconnecting nodal masses with adjustable springs. Acting as mobile sampling sites, the nodes observe properties of the input data, such as intensities, depths, gradients, and curvatures. Based on these nodal observations, the springs automatically adjust their stiffnesses so as to distribute the available degrees of freedom of the reconstructed model in accordance with the local complexity of the input data. The adaptive mesh algorithm runs at interactive rates with continuous 3-D display on a graphics workstation It is applied to the adaptive sampling and reconstruction of images and surfaces.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Dynamic stereo in visual navigation
Authors: Massimo Tistarelli, Enrico Grosso, Giulio Sandini
Venue: CVPR
Year: 1991

A cooperative schema is proposed in which binocular disparity, computed on several stereo images over time, is combined with optical flow from the same sequence to obtain a relative-depth map of the scene. Both time-to-impact and depth scaled by the distance of the camera from the fixation point in space are considered as good, relative measurements which are based on the viewer (but centered on the environment). Two experiments, performed on image sequences from real scenes, are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Object detection using contrast based scale-space
Authors: Vijaykumar A. Topkar, Arun K. Sood, B. Kjell
Venue: CVPR
Year: 1991

The authors propose four scale-space object detection algorithms for separating objects from the background. These algorithms do not need thresholding at any of the scales. The different algorithms are applicable to images with different noise and clutter characteristics. Statistical analysis of the four algorithms is conducted for noisy and cluttered backgrounds.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Segmentation and grouping of object boundaries using energy minimization
Authors: Deborah Anne Trytten, Mihran Tüceryan
Venue: CVPR
Year: 1991

An algorithm is described which performs curvilinear grouping of image edge elements for detecting object boundaries. The method works by generating hypotheses and selecting the best one. A neighborhood definition based on Delaunay graph is used to keep the number of generated hypotheses small. An energy minimizing curve is fit to the generated hypotheses to evaluate the grouping and locate discontinuities.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Recovering shape from contour for constant cross section generalized cylinders
Authors: Fatih Ulupinar, Ramakant Nevatia
Venue: CVPR
Year: 1991

The authors analyze the properties of constant cross section generalized cylinders (CGCs), and derive the types of symmetries that the limb boundaries and cross sections of these objects produce on the image plane. The constraints on the 3-D shape of the objects are formulated based on the symmetries and from the geometry of the projection models. The methods that recover the 3-D shape from the image of their contours are discussed and recovered surfaces are shown for sample objects.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Stereopsis and image registration from extended edge features in the absence of camera pose information
Authors: Nitin M. Vaidya, Kim L. Boyer
Venue: CVPR
Year: 1991

The authors solve the stereo correspondence problem in uncalibrated domains using extended edge contours as a source of primitives, as opposed to traditional point-based algorithms. This work represents a novel approach to implementation of the structural stereopsis concept of K.L. Boyr and A.C. Kak (1988), in particular with regard to speed. Judiciously exploiting the contiguity relation among primitives, correspondence solutions without prior knowledge of the epipolar condition for feature-rich stereopairs, previously requiring several days of processing by the Boyer and Kak algorithm are now acquired in tens of seconds on the same equipment.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Fractal probability functions-an application to image analysis
Authors: Jacques Lévy Véhel
Venue: CVPR
Year: 1991

The extension of the iterated function system (IFS) theory dealing with probability functions instead of numbers is applied to texture analysis. The results allow encoding and reconstruction of textured images, and hence the compression of data to tackle the problem of texture segmentation in a rigorous manner.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Surface and motion estimation from sparse range data
Authors: Baba C. Vemuri, Gunleiv Skofteland
Venue: CVPR
Year: 1991

A system is presented for the simultaneous estimation of surface and motion parameters of a free-flying object in a telerobotics experiment. The system consists of two main components, a vision-based invariant-surface and motion estimator, and a Kalman filter. An algorithm for invariant surface and motion estimation from sparse multi-sensor range data is presented. Motion estimates from the vision module are input to a Kalman filter (KF) for tracking a 'free-flying' object in space. The predicted motion parameters from the KF are fed back to the vision module and serve as an initial guess in the search for optimal motion.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Deformable models: canonical parameters for surface representation and multiple view integration
Authors: B. C. Vermuri, R. Malladi
Venue: CVPR
Year: 1991

Three-dimensional viewpoint invariance is an important requirement in the representation of surfaces for recognition tasks. Parameterized surfaces possess this desirable property. In general, the parameters in a parametric surface representation can be arbitrarily defined. A canonical, intrinsic parameterization provides a consistent, invariant form for describing surfaces. The goal of this work is to define and construct such a parameterization.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Efficiently using invariant theory for model-based matching
Authors: Peter C. Wayner
Venue: CVPR
Year: 1991

A method is presented for efficiently maintaining and searching a database of three-dimensional models so they can be reliably recognized from arbitrary two-dimensional projections in the presence of noise and occlusion. The core of the process is the topologically defined network of invariants which breaks three-dimensional models down into small, local groups of features and indexes these groups using functions that are invariant under translation, rotation, scaling, and orthographic projection. The network encodes the geometrical relationships between these groups so that grouping information can be used to increase the speed of matching.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Two plane camera calibration: a unified model
Authors: Guo-Qing Wei, Song De Ma
Venue: CVPR
Year: 1991

A unified model for camera calibration is presented. The model does not assume any explicit form of imaging process and can perform linear back projection while considering all lens distortions. This model is well suited to stereo reconstruction. It has been shown that the original two-plane model, the linear and nonlinear pin hole model, can all be realized as special cases of this model. With the two-plane model, optimal orientation of the two reference planes can be found intuitively.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
How accurately can direct motion vision determine depth?
Authors: E. J. Weldon Jr., Hui Liu
Venue: CVPR
Year: 1991

The use of direct motion vision for determining the depth of a scene is investigated. To permit direct comparison of analytical and experimental results, only translational motion and planar patches of constant depth are considered. The analysis shows that the accuracy with which depth can be determined increases with the sum of the squares of the temporal derivatives over the patch; this quantity is referred to as the apparent size of the patch. After determining the relationship between relative depth error and apparent size analytically, a number of experiments with camera-generated image sequences were performed. In nearly all of these experiments, the agreement between the analytically determined and measured values of the relative depth error is very good.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
MAP model matching
Authors: William M. Wells III
Venue: CVPR
Year: 1991

A simple MAP model-matching criterion that captures important aspects of recognition in controlled situations is described. A detailed metrical object model is assumed. A probabilistic model of image features is combined with a simple prior on both the pose and the feature interpretations to yield a mixed objective function. The parameters that appear in the probabilistic models can be derived from images in the application domain. By extremizing the objective function, an optimal matching between model and image feature results. Within this framework, good models of feature uncertainty allow for robustness despite inaccuracy in feature detection. In addition, the relative likelihood of features arising from either the object or the background can be evaluated in a rational way. The objective function provides a simple and uniform means of evaluating match and pose hypotheses. Several linear projection and feature models are discussed. An experimental implementation of MAP model matching, among features derived from low-resolution edge images, is described.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Real-time generation of environmental map and obstacle avoidance using omnidirectional image sensor with conic mirror
Authors: Yasushi Yagi, Masahiko Yachida
Venue: CVPR
Year: 1991

An omnidirectional image sensor COPIS (conic projection image sensor) is proposed for guiding navigation of a mobile robot. It features passive sensing of the omnidirectional environment in real-time using a conic mirror. Because the conic mirror is used, its image is under conic projection; where the azimuth of each point in the scene appears in the image as its direction from the image center. The authors describe COPIS and its application to guide the navigation of a mobile robot. The COPIS system acquires an omnidirectional view around the robot in real-time by using a conic mirror. Under the assumption of constant motion of the robot, locations of objects around the robot can be estimated by detecting their azimuth changes in the omnidirectional image. Using this method, the robot generates an environmental map of an indoor scene while it is moving in the environment. A method to avoid collision against objects by detecting their azimuth changes is presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Human motion analysis based on a robot arm model
Authors: Masanobu Yamamoto, Kazutada Koshikawa
Venue: CVPR
Year: 1991

A model-based method for analyzing a human body motion is presented. The method is based on a robot arm model which represents a human body motion. Combining the model and the gradient scheme, the movement of the configuration of the model (Human) can be directly estimated from an image sequence.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Sources from shading
Authors: Yihing Yang, Alan L. Yuille
Venue: CVPR
Year: 1991

The authors assume a Lambertian shading model with unknown light source directions. It is shown that information on the occluding boundary puts strong constraints on the light source directions. For a small number of light sources, from sufficiently different directions, additional information from intensity extrema will be sufficient to determine the source directions. If there are two, or three, views of the object then the light sources can be determined without extrema information. The authors report experiments performed on synthesized images.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>