By Topic

Computer Vision and Pattern Recognition, 1992. Proceedings CVPR '92., 1992 IEEE Computer Society Conference on

Date 15-18 June 1992

Filter Results

Displaying Results 1 - 25 of 160
  • Indexing function-based categories for generic recognition

    Page(s): 795 - 797
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (292 KB)  

    The authors report the implementation and evaluation of a function-based recognition system that takes an uninterrupted 3-D object shape as its input and reasons to determine if the object belongs to the superordinate category furniture, and if so, into which (sub)category it falls. The system has analyzed over 250 input objects, and the results largely agree with intuitive human interpretation of the objects. The study confirms that a relatively small number of knowledge primitives may be used as the basis for defining a relatively broad range of object categories. The greatest derivation from intuitive human interpretation occurs with objects that humans would not typically label as one of the known categories defined, but which have some novel orientation in which they could serve the function of one of these categories. This is because the system uses a purely function-based definition of the object category.<> View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Proceedings. 1992 IEEE Computer Society Conference on Computer Vision and Pattern Recognition (Cat. No.92CH3168-2)

    Save to Project icon | Request Permissions | PDF file iconPDF (20 KB)  
    Freely Available from IEEE
  • The scale space aspect graph

    Page(s): 335 - 340
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (488 KB)  

    Currently the aspect graph is computed under the assumption of perfect resolution in the viewpoint, the projected image, and the object shape. Visual detail is represented that an observer might never see in practice. By introducing scale into this framework, a mechanism is provided for selecting levels of detail that are large enough to merit explicit representation, effectively allowing control over the size of the aspect graph. To this end the scale space aspect graph is introduced, and an interpretation of the scale dimension in terms of the spatial extent of image features is considered. A brief example is given for polygons in a plane.<> View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Saliencies and symmetries: toward 3D object recognition from large model databases

    Page(s): 322 - 327
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (509 KB)  

    The construction of interpretation tables from database models is introduced, and a recognition procedure using scene feature groups is discussed. Techniques for extraction of feature group equivalence classes and computation of feature group saliency are discussed. Two methods to reduce the computational burdens associated with a large model database are proposed and tested on polyhedral objects. The first method reduces the population of protohypotheses in the interpretation tables consulted during recognition by excluding redundant feature groups produced from object symmetries. The second method assigns a population-based numerical measure of saliency to each feature group retrieved from the scene; this measure allows only the most salient feature groups to be used in object recognition.<> View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Hierarchical waveform matching: a new feature-based stereo technique

    Page(s): 513 - 519
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (864 KB)  

    A feature-based stereo matching system that is based on an algorithm for one-dimensional waveform matching is described. It is intended for use in automated cartography, to generate an accurate three-dimensional model of man-made structures and natural terrain. Each epipolar line in the stereo pair is represented as a one-dimensional intensity waveform. The waveform is described as a collection of features, such as peaks and valleys, and represented across a set of hierarchical levels, computed by approximation from the original waveform. These features are matched using an evaluation function that factors similarity of waveform shape, intensity, and symbolic feature description. Waveform matches at coarse resolution are used to constrain matches at finer levels. Intra/inter-scanline corrections are applied and the actual position of the stereo match is adjusted by using the gradient representation of the original waveform. Some representative results are presented for a complex urban scene View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Recovering the scaling function of a SHGC from a single perspective view

    Page(s): 36 - 41
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (388 KB)  

    An algorithm for recovering the scaling function of a straight homogeneous generalized cylinder (SHGC) from an image contour is presented. Both location and reference cross section are supposed known. Perspective view assumption and geometric properties of SHGCs are used to derive the method. No additional constraints have been imposed on the object shape. The method has been tested on synthetic image, with promising results View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Direct method for reconstructing shape from shading

    Page(s): 453 - 458
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (564 KB)  

    An approach to shape-from-shading that is based on a connection with a calculus of variations/optimal control problem is proposed. An explicit representation corresponding to a shaded image is given for the surface; uniqueness of the surface (under suitable conditions) is an immediate consequence. The approach leads naturally to an algorithm for shape reconstruction that is simple, fast, provably convergent (in many cases, provably convergent to the correct solution), and does not require regularization. Given a continuous image, the algorithm can be proved to converge to the continuous surface solution as the image sampling frequency is taken to infinity. Experimental results are presented for synthetic and real images View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Task-specific utility in a general Bayes net vision system

    Page(s): 142 - 147
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (612 KB)  

    TEA is a task-oriented computer vision system that uses Bayes nets and a maximum expected-utility decision rule to choose a sequence of task-dependent and opportunistic visual operations on the basis of their cost and (present and future) benefit. The authors discuss technical problems regarding utilities, present TEA-1's utility function (which approximates a two-step lookahead), and compare it to various simpler utility functions in experiments with real and simulated scenes View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Active photometric stereo

    Page(s): 29 - 34
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (608 KB)  

    An active vision technique for determining the absolute depth of surfaces is described. The algorithm assumes a very general model for the reflectance properties of the surface, and is valid for most of the shading models commonly used in computer vision work. The algorithm relies on the controlled motion of a point light source, which is not at infinity but relatively close to the surface and to the camera. The sensitivity of the computed depth values to errors in the measured quantities is derived, allowing a confidence measure for the depth to be determined. The confidence measure can aid in the estimation of accurate depth values from multiple image measurements taken over time. A method based on robust estimation that permits an unbiased estimate of the depth values to be obtained is presented. The results of experiments on synthetic and real-world imagery are reported, illustrating the efficacy of the active photometric stereo algorithm View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Model based region segmentation using cooccurrence matrices

    Page(s): 636 - 639
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (396 KB)  

    A region segmentation algorithm is presented, using a model for joint probability density. Joint probability density can be defined as an N×N cooccurrence matrix in which each coordinate (i, j) gives the probability for the gray-level transition i, j between two neighbor pixels. The approach consists in modeling the energy distribution within a cooccurrence matrix of a region. Regions are assumed to be stationary. A region-growing scheme that proceeds in two steps is used. The first step consists of learning the parameters of the model. The second step is the segmentation process. Starting with a seed pixel, new pixels are incorporated in the region if their neighborhoods fit the model View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Shape reconstruction from photometric stereo

    Page(s): 479 - 484
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (508 KB)  

    Two iterative algorithms for shape reconstruction based on multiple images taken under different lighting conditions, known as photometric stereo, are proposed. It is shown that single-image shape-from-shading (SFS) algorithms have an inherent problem, i.e., the accuracy of the reconstructed surface height is related to the slope of the reflectance map function defined on the gradient space. This observation motivates the authors to generalize the single-image SFS algorithm to two photometric stereo SFS algorithms aiming at more accurate surface reconstruction. The two algorithms directly determine the surface height by minimizing a quadratic cost functional, which is defined to be the square of the brightness error obtained from each individual image in a parallel or cascade manner. The optimal illumination condition that leads to best shape reconstruction is examined View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Neural network models for illusory contour perception

    Page(s): 681 - 683
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (252 KB)  

    A physiologically motivated model of illusory contour perception is examined by simulating a neural network architecture that was tested with gray-level images. The results indicate that a model that combines a bottom-up feature aggregation strategy with recurrent processing is best suited for describing this type of perceptual completion View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Analysis of the least median of squares estimator for computer vision applications

    Page(s): 621 - 623
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (252 KB)  

    The robust least-median-of-squares (LMedS) estimator, which can recover a model representing only half the data points, was recently introduced in computer vision. Image data, however, is usually also corrupted by a zero-mean random process (noise) accounting for the measurement uncertainties. It is shown that in the presence of significant noise, LMedS loses its high breakdown point property. A different, two-stage approach in which the uncertainty due to noise is reduced before applying the simplest LMedS procedure is proposed. The superior performance of the technique is proved by comparative graphs View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Computing curvilinear structure by token-based grouping

    Page(s): 264 - 270
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (728 KB)  

    A computational framework for computing curvilinear structure on the edge data of images is presented. The method is symbolic, operating on geometric entities/tokens. It is also constructive, hierarchical, parallel, and locally distributed. Computation proceeds independently at each token and at each stage interleaves the discovery of structure with its careful description. The process yields a hierarchy of descriptions at multiple scales. These multiscale descriptions provide efficient feature indexing both for the grouping process itself as well as for subsequent recognition processes. Experimental results are presented to demonstrate the effectiveness of the approach with respect to curvilinear structure, and its application to more general grouping problems is discussed View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Kinematic calibration of an active camera system

    Page(s): 748 - 751
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (312 KB)  

    A technique for the calibration of an active camera system is presented. The calibration of manipulator, camera-to-manipulator, camera, and base-to-world is treated in a unified and elegant way. In this approach, the camera frames and manipulator link frames are all related to the world frame, therefore the camera-to-manipulator and base-to-world calibration is very straightforward. The approach is simple, since it uses the form of one equation solving one parameter. Two experiments that verify the accuracy of the technique are reported View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A MRF approach to optical flow estimation

    Page(s): 853 - 856
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (304 KB)  

    A Markov random field (MRF) formulation for the problem of optical flow computation is studied. An adaptive window matching scheme is used to obtain a good measure of the correlation between the two images. A confidence measure for each match is also used. Thus, the input to the system is the adaptive correlation and the corresponding confidence. The MRF model is then used to estimate the velocity field and the velocity discontinuities. The problem of occlusions is addressed, and a relationship between occlusions and motion discontinuities is established View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Performance of optical flow techniques

    Page(s): 236 - 242
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (724 KB)  

    The performance of six optical flow techniques is compared, emphasizing measurement accuracy. The most accurate methods are found to be the local differential approaches, where ν is computed explicitly in terms of a locally constant or linear model. Techniques using global smoothness constraints appear to produce visually attractive flow fields, but in general seem to be accurate enough for qualitative use only and insufficient as precursors to the computations of egomotion and 3D structures. It is found that some form of confidence measure/threshold is crucial for all techniques in order to separate the inaccurate from the accurate. Drawbacks of the six techniques are discussed View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Adaptive-size physically-based models for nonrigid motion analysis

    Page(s): 833 - 835
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (292 KB)  

    Adaptive-size physically based models suitable for nonrigid motion analysis are presented. The mesh size increases or decreases dynamically during the surface reconstruction process to locate nodes near surface areas of interests (like high curvature points) and to optimize the fitting error. A priori information about nonrigidity can be included so that the surface model deforms to fit moving data points while preserving some basic nonrigid constraints (e.g. isometry or conformality). Implementation of the proposed algorithm with and without isometric/conformal constraints is presented. Performance and accuracy of derived algorithms are demonstrated on data simulating deforming ellipsoidal and bending planar shapes. The algorithm is applied to the real range data for bending paper and to volumetric temporal left ventricular data View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Efficient model library access by projectively invariant indexing functions

    Page(s): 109 - 114
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (740 KB)  

    Projectively invariant shape descriptors allow fast indexing into model libraries without the need for pose computation or camera calibration. Progress in building a model-based vision system for plane objects that uses algebraic projective invariants is described. A brief account of these descriptors is given, and the recognition system is described, giving examples of the invariant techniques working on real images View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Correcting chromatic aberrations using image warping

    Page(s): 684 - 687
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (392 KB)  

    The use of image warping to reduce the impact of chromatic aberration in vision applications is addressed. The warp is determined using edge displacements which are fit with cubic splines. An image reconstruction algorithm is used for nonlinear resampling. The main contribution of this work is to analyze the quality of the warping approach by comparing it with active lens control. Test results for two different imaging systems are reported View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Controlling illumination color to enhance object discriminability

    Page(s): 710 - 712
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (208 KB)  

    The authors describe how to design color illumination to improve the discriminability of objects in color images. This procedure is useful in applications where the illumination can be controlled, such as inspection tasks. From the physics of color image formation, the optimal color illumination for discriminating materials is derived using a parametrically defined set of illuminants. The authors suggest how such an approach might be extended to sets of materials and more general classes of light sources. Experiments with painted color patches and live potato plantlets are used to illustrate the usefulness of actively controlling illumination color in machine vision View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Diffuse reflection [intensity reflectance model]

    Page(s): 472 - 478
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (672 KB)  

    An intensity reflectance model is proposed for diffuse reflection originating from subsurface multiple scattering within inhomogeneous dielectric materials. One of the most common assumptions in computer vision from inhomogeneous dielectrics is Lambertian. The proposed model utilizes the subsurface intensity distribution predicted by modeling subsurface multiple scattering based upon radiative transfer theory. For an optically smooth surface boundary this subsurface intensity distribution becomes altered by Fresnel attenuation upon refraction into air, making it become significantly non-Lambertian. This resulting intensity distribution serves as a reflection law for individual optically smooth microfacets that compose an opaque rough surface, producing a physical unification of diffuse reflection with the Torrance-Sparrow specular reflection model. Experimental results that verify the accuracy of the model are presented. A relatively simple formula that approximates closely the true behaviour of diffuse reflection and can be used in place of a Lambertian term is presented. The non-Lambertian nature of the diffuse component becomes most significant near occluding contours and sometimes produces a previously unnoticed intensity effect that can aid in their detection View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • The alignment of objects with smooth surfaces: error analysis of the curvature method

    Page(s): 341 - 346
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (376 KB)  

    The recognition of objects with smooth bounding surfaces from their contour images is addressed. In particular, the curvature method is applied to ellipsoidal objects and the error for different rotations of the objects is computed analytically. It is seen that the error depends on the exact shape of the ellipsoid (namely, the relative lengths of its axes), and it increases as the ellipsoid becomes elongated in the Z-direction. It is shown that the errors are usually small, and that, in general, a small number of models is required to predict the appearance of an ellipsoid from all possible views View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Local reproducible smoothing without shrinkage

    Page(s): 277 - 282
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (464 KB)  

    A simple local smoothing filter for curves or surfaces, combining the advantages of Gaussian smoothing and Fourier curve description, is defined. Unlike Gaussian filters, the filter described has no shrinkage problem. Repeated application of the filter does not yield a curve or surface smaller than the original, but simply reproduces the approximate result that would have been obtained by a single application at the largest scale. Unlike Fourier description, the filter is local in space. The wavelet transform of Y. Meyer (1989) is shown to have these properties View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Vector field analysis for oriented patterns

    Page(s): 673 - 676
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (532 KB)  

    A method based on the properties of orientation fields is presented for the estimation of a set of symbolic descriptors from nondegenerate linear orientation fields, modeled by two-dimensional first-order phase portraits. It was previously shown that flow orientation is sufficient to characterize a flow pattern and locate its critical point position. A linear estimator is designed to estimate nondegenerate phase portraits. A classification scheme based on their local properties-curl, divergence, and deformation-is developed. Some experimental results are reported View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.