OpenRaiser/Intern-Atlas huggingface dataset:
Model-Based 2D&3D Dominant Motion Estimation for Mosaicing and Video Representation
Authors: Harpreet S. Sawhney, Serge Ayer, Monika Gorkani
Venue: ICCV
Year: 1995

It is fairly common in video sequences that a mostly fixed background (scene) is imaged with or without objects. The dominant background changes in the image plane mostly due to camera operations and motion (zoom, pan, tilt, track etc.). We address the problem of computation of the dominant image transformation over time and demonstrate how this can be effectively used for efficient video representation through video mosaicing and image registration. We formulate the problem of dominant component estimation as that of model based robust estimation using M estimators with direct, multi resolution methods. In addition to 2D affine and plane projective models, that have been used in the past for describing image motion using direct methods, we also employ a true 3D model of motion and scene structure imaged with uncalibrated cameras. This model parameterizes the image motion as that due to a planar component and a parallax component. For rigid 3D scenes imaged under camera motion only, least squares (LS) methods with the plane and parallax parameterization are also presented. Furthermore, in the context of robust estimation, in contrast with previous approaches for similar problems, our algorithm employs an automatic computation of a scale parameter that is crucial in rejecting the non dominant components as outliers.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Optimal Subpixel Matching of Contour Chains and Segments
Authors: Bruno Serra, Marc Berthod
Venue: ICCV
Year: 1995

This paper introduces a new general purpose algorithm that allows the optimal geometric match between contours to be determined, that is the transformation yielding a minimal deformation is obtained. The algorithm relies only on the geometric properties of the contours and does not call for any other constraint, so that it is particularly suitable when no parameterization of title deformation is available or desirable. Contour deformation is explicitly incorporated in the computation, allowing for a thorough use of all geometric information available. Moreover, no discretization is involved in the computation, resulting in two main advantages: first, the algorithm is robust to differences in the segmentation of contours and allows the matching of polygonal approximations of contours with very little loss of precision, second, subpixel precision matching can be achieved.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Trilinearity of Three Perspective Views and its Associated Tensor
Authors: Amnon Shashua, Michael Werman
Venue: ICCV
Year: 1995

It has been established that certain trilinear forms of three perspective views give rise to a tensor of 27 intrinsic coefficients. We show in this paper that a permutation of the the trilinear coefficients produces three homography matrices (projective transformations of planes) of three distinct intrinsic planes, respectively. This, in turn, yields the result that 3D invariants are recovered directly-simply by appropriate arrangement of the tensor's coefficients. On a secondary level, we show new relations between fundamental matrix, epipoles, Euclidean structure and the trilinear tensor. On the practical side, the new results extend the existing envelope of methods of 3D recovery from 2D views-for example, new linear methods that cut through the epipolar geometry, and new methods for computing epipolar geometry using redundancy available across many views.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Probabilistic 3D Object Recognition
Authors: Ilan Shimshoni, Jean Ponce
Venue: ICCV
Year: 1995

A probabilistic 3D object recognition algorithm is presented. In order to guide the recognition process the probability that match hypotheses between image features and model features are correct is computed. A model is developed which uses the probabilistic peaking effect of measured angles and ratios of lengths by tracing iso angle and iso ratio curves on the viewing sphere. The model also accounts for various types of uncertainty in the input such as incomplete and inexact edge detection. For each match hypothesis the pose of the object and the pose uncertainty which is due to the uncertainty in vertex position are recovered. This is used to find sets of hypotheses which reinforce each other by matching features of the same object with compatible uncertainty subsets. A probabalistic expression is used to rank these hypothesis sets. The hypothesis sets with the highest rank are output. The algorithm has been fully implemented, and tested on real images.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
An Integral Approach to Free-Formed Object Modeling
Authors: Heung-Yeung Shum, Martial Hebert, Katsushi Ikeuchi, Raj Reddy
Venue: ICCV
Year: 1995

Presents a new approach to free-formed object modeling from multiple range images. In most conventional approaches, successive views are registered sequentially. In contrast to the sequential approaches, we propose an integral approach which reconstructs statistically optimal object models by simultaneously aggregating all data from multiple views into a weighted least-squares (WLS) formulation. The integral approach has two components. First, a global resampling algorithm constructs partial representations of the object from individual views so that correspondences can be established among different views. The global resampling algorithm is based on the spherical attribute image (SAI) previously introduced in the context of object representation and recognition. Second, a weighted least-squares algorithm integrates resampled partial representations of multiple views, using the technique of principal component analysis with missing data (PCAMD). Experiments using real range images show that our approach is robust against noise and mismatches, and generates accurate object models.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Steerable Wedge Filters
Authors: Eero P. Simoncelli, Hany Farid
Venue: ICCV
Year: 1995

Steerable filters, as developed by Freeman and Adelson (1991), are a class of rotation-invariant linear operators that may be used to analyze local orientation patterns in imagery. The most common examples of such operators are directional derivatives of Gaussians and their 2D Hilbert transforms. The inherent symmetry of these filters produces an orientation response that is periodic with period /spl pi/, even when the underlying image structure does not have such symmetry. This problem may be alleviated by reconsidering the full class of steerable filters. We develop a family of even- and odd-symmetric steerable filters that have a spatially asymmetric "wedge-like" shape and are optimally localized in their orientation response. Unlike the original steerable filters, these filters are not based on directional derivatives and the Hilbert transform relationship is imposed on their angular components. We demonstrate the ability of these filters to properly represent oriented structures.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Combining Color and Geometric Information for the Illumination Invariant Recognition of 3D Objects
Authors: David Slater, Glenn Healey
Venue: ICCV
Year: 1995

Traditional approaches to three dimensional object recognition exploit the relationship between three dimensional object geometry and two dimensional image geometry. The capability of object recognition systems can be improved by also incorporating information about the color of object surfaces. We derive invariants of local color pixel distributions that are independent of viewpoint and the configuration, intensity, and spectral content of the scene illumination. These invariants capture information about the distribution of spectral reflectance which is intrinsic to a surface and thereby provide substantial discriminatory power for identifying a wide range of surfaces. These invariants can be computed efficiently from color image regions without requiring any form of segmentation. We have implemented an object recognition system that indexes into a database of models using the invariants and that uses associated geometric information for hypothesis verification and pose estimation. The approach to recognition is based on the computation of local invariants and is therefore relatively insensitive to occlusion. We present several examples demonstrating the system's ability to recognize model objects in cluttered scenes. The discriminatory power of the invariants has been demonstrated by the system's ability to process a large set of regions over complex scenes without generating false hypotheses.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
ASSET-2: Real-Time Motion Segmentation and Shape Tracking
Authors: Stephen M. Smith 0001
Venue: ICCV
Year: 1995

The paper describes how image sequences taken by a moving video camera may be processed to detect and track moving objects against a moving background in real-time. The motion segmentation and shape tracking system as known as ASSET-2-A Scene Segmenter Establishing Tracking, Version 2. Motion is found by tracking image features, and segmentation is based on first-order (i.e., six parameter) flow fields. Shape tracking is performed using two dimensional radial map representation. The system runs in real-time, and is accurate and reliable. It requires no camera calibration and no knowledge of the camera's motion.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Limitations of Markov Random Fields as Models of Textured Images of Real Surfaces
Authors: Athanasios Speis, Glenn Healey
Venue: ICCV
Year: 1995

We investigate to what extent textures can be distinguished using conditional Markov fields and small samples. We establish that the least square (LS) estimator is the only reasonable choice for this task and we prove its asymptotic consistency and normality for a general class of random fields that include Gaussian Markov fields as a special case. The performance of this estimator when applied to textured images of real surfaces is poor if small boxes are used (20/spl times/20 or less). We investigate the nature of this problem by comparing the behavior predicted by the rigorous theory to the one that has been experimentally observed. Our analysis reveal that 20/spl times/20 samples contain enough information to distinguish between the textures in our experiments and that the poor performance mentioned above should be attributed to the fact that conditional Markov fields do not provide accurate models for textured images of many real surfaces. A more general model that exploits more efficiently the information contained in small samples is also suggested.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Accurate Internal Camera Calibration Using Rotation, with Analysis of Sources of Error
Authors: Gideon P. Stein
Venue: ICCV
Year: 1995

Describes a simple and accurate method for internal camera calibration based on tracking image features through a sequence of images while the camera undergoes pure rotation. A special calibration object is not required and the method can therefore be used both for laboratory calibration and for self calibration in autonomous robots. Experimental results with real images show that focal length and aspect ratio can be found to within 0.15 percent, and lens distortion error can be reduced to a fraction of a pixel. The location of the principal point and the location of the center of radial distortion can each be found to within a few pixels. We perform a simple analysis to show to what extent the various technical details affect the accuracy of the results. We show that having pure rotation is important if the features are derived from objects close to the camera. In the basic method accurate angle measurement is important. The need to accurately measure the angles can be eliminated by rotating the camera through a complete circle while taking an overlapping sequence of images and using the constraint that the sum of the angles must equal 960 degrees.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Robot Aerobics: Four Easy Steps to a More Flexible Calibration
Authors: Daniel E. Stevenson, Margaret M. Fleck
Venue: ICCV
Year: 1995

Presents a method for calibrating intrinsic and extrinsic camera parameters. This algorithm can easily be modified by other users to suit their particular calibration needs, without requiring a high-precision calibration target or complicated linear algebra. The algorithm uses controlled motions and a single light source to simulate calibration targets in convenient 3D locations. These convenient calibration targets enable us to simplify the calibration algorithm and gather dense data for lens distortion. Dense data makes the distortion correction more accurate than traditional low-order polynomial fits, and allows us to calibrate wide-angle lenses (>70/spl deg/ field of view).< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Motion Estimation with Quadtree Splines
Authors: Richard Szeliski, Heung-Yeung Shum
Venue: ICCV
Year: 1995

This paper presents a motion estimation algorithm based on a new multiresolution representation, the quadtree spline. This representation describes the motion field as a collection of smoothly connected patches of varying size, where the patch size is automatically adapted to the complexity of the underlying motion. The topology of the patches is determined by a quadtree data structure, and both split and merge techniques are developed for estimating this spatial subdivision. The quadtree spline is implemented using another novel representation, the adaptive hierarchical basis spline, and combines the advantages of adaptively-sized correlation windows with the speedups obtained with hierarchical basis preconditioners. Results are presented on some standard motion sequences.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
A Geometric Criterion for Shape-Based Non-Rigid Correspondence
Authors: Hemant D. Tagare, Donal O&apos, Shea, Anand Rangarajan 0001
Venue: ICCV
Year: 1995

A geometric criterion is developed for establishing shape based non rigid correspondence between plane curves. Unlike previous efforts, the criterion does not use rigid invariants of shape. Instead, shapes are compared non rigidly from the vantage point of the correspondence. Geometric invariants are proposed for curves whose shapes can be exactly matched by a non rigid correspondence. The invariants are based on angular deviations of convex and concave segments of the curves. Examples of correspondences between curves obtained from medical images are provided.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Curve and Surface Smoothing without Shrinkage
Authors: Gabriel Taubin
Venue: ICCV
Year: 1995

For a number of computational purposes, including visualization of scientific data and registration of multimodal medical data, smooth curves must be approximated by polygonal curves, and surfaces by polyhedral surfaces. An inherent problem of these approximation algorithms is that the resulting curves and surfaces appear faceted. Boundary-following and iso-surface construction algorithms are typical examples. To reduce the apparent faceting, smoothing methods are used. In this paper, we introduce a new method for smoothing piecewise linear shapes of arbitrary dimension and topology. This new method is in fact a linear low-pass filter that removes high-curvature variations, and does not produce shrinkage. Its computational complexity is linear in the number of edges or faces of the shape, and the required storage is linear in the number of vertices.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Image Segmentation by Reaction-Diffusion Bubbles
Authors: Hüseyin Tek, Benjamin B. Kimia
Venue: ICCV
Year: 1995

Figure-ground segmentation is a fundamental problem in computer vision. The main difficulty is the integration of low-level, pixel-based local image features to obtain global object-based descriptions. Active contours in the form of snakes, balloons, and level-set modeling techniques have been proposed that satisfactorily address this question for certain applications. However, these methods require manual initialization, do not always perform well near sharp protrusions or indentations, or often cross gaps. We propose an approach inspired by these methods and a shock-based representation of shape in terms of parts, protrusions, and bends. Since initially it is not clear where the objects or their parts are, parts are hypothesized in the form of fourth order shocks randomly initialized in homogeneous areas of images. These shocks then form evolving contours, or bubbles, which grow, shrink, merge, split and disappear to capture the objects in the image. In the homogeneous areas of the image bubbles deform by a reaction-diffusion process. In the inhomogeneous areas, indicated by differential properties computed from low-level processes such as edge-detection, texture, optical-flow and stereo, etc., bubbles do not deform. As such, the randomly initialized bubbles integrate low-level information and, in the process, segment the figures from the ground.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Recovering 3D Motion of Multiple Objects Using Adaptive Hough Transform
Authors: Tina Yu Tian, Mubarak Shah
Venue: ICCV
Year: 1995

Presents a method to determine the 3D motion of multiple objects from two perspective views. In our method, segmentation is determined based on a 3D rigidity constraint. We divide the input image into overlapping patches, and for each sample of the translation parameter space, we compute the rotation parameters of patches using a least-squares fit. Every patch votes for a sample in the translation and rotation parameter space. For a patch containing multiple motions, we use an M-estimator to compute rotation parameters of a dominant motion. We use the adaptive Hough transform to refine the relevant parameter space in a "coarse-to-fine" fashion. Applications of the proposed method to both synthetic and real images are demonstrated with promising results.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Computation of Coherent Optical Flow by Using Multiple Constraints
Authors: Massimo Tistarelli
Venue: ICCV
Year: 1995

The optical flow constitutes one of the most widely adopted representations to define and characterize the evolution of image features over time. In order to compute the velocity field, it is necessary to define a set of constraints on the temporal change of image features. We consider the implications in using multiple constraints arising from multiple data points. The first step is the analysis of differential constraints and how they can be applied, locally, to compute the image velocity. This analysis allows to relate each constraint to a particular gray level pattern. This approach is extended to multiple image points, allowing also the characterization of the temporal behaviour of the image features and to detect erroneous measurements due to occlusions, depth discontinuities or shadows. Several experiments are presented from real image sequences. >
Robust Detection of Degenerate Configurations for the Fundamental Matrix
Authors: Philip H. S. Torr, Andrew Zisserman, Stephen J. Maybank
Venue: ICCV
Year: 1995

New methods are reported for the detection of multiple solutions (degeneracy) when estimating the fundamental matrix, with specific emphasis on robustness in the presence of data contamination (outliers). The fundamental matrix can be used as a first step in the recovery of structure from motion. If the set of correspondences is degenerate then this structure cannot be accurately recovered and many solutions will explain the data equally well. It is essential that we are alerted to such eventualities. However, current feature matchers are very prone to mismatching, giving a high rate of contamination within the data. Such contamination can make a degenerate data set appear non degenerate, thus the need for robust methods becomes apparent. The paper presents such methods with a particular emphasis on providing a method that will work on real imagery and with an automated (non perfect) feature detector and matcher. It is demonstrated that proper modelling of degeneracy in the presence of outliers enables the detection of outliers which would otherwise be missed. Results using real image sequences are presented. All processing, point matching, degeneracy detection and outlier detection is automatic.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>
Towards an Active Visual Observer
Authors: Tomas Uhlin, Peter Nordlund, Atsuto Maki, Jan-Olof Eklundh
Venue: ICCV
Year: 1995

We present a binocular active vision system that can attend to and fixate a moving target. Our system has an open and expandable design and it forms the first steps of a long term effort towards developing an active observer using vision to interact with the environment, in particular capable of figure-ground segmentation. We also present partial real-time implementations of this system and show their performance in real-world situations together with motor control. In pursuit we particularly focus on occlusions of other targets, both stationary and moving, and integrate three cues, ego-motion, target motion and target disparity, to obtain an overall robust behavior. An active vision system must be open, expandable, and operate with whatever data are available momentarily. It must also be equipped with means and methods to direct and change its attention. This system is therefore equipped with motion detection for changing attention and pursuit for maintaining attention, both of which run concurrently.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">></ETX>