Showing papers on "Orientation (computer vision) published in 1991"

The Plenoptic Function and the Elements of Early Vision

Abstract: What are the elements of early vision? This question might be taken to mean, What are the fundamental atoms of vision?—and might be variously answered in terms ofsuch candidate structures as edges, peaks, corners, and so on. In this chapter we adopt a rather different point of view and ask the question, What are the fundamentalsubstances of vision? This distinction is important becausewe wish to focus on the first steps in extraction of visualinformation. At this level it is premature to talk aboutdiscrete objects, even such simple ones as edges and corners.There is general agreement that early vision involvesmeasurements of a number of basic image properties in-cluding orientation, color, motion, and so on. Figure l.lshows a caricature (in the style of Neisser, 1976), of the sort of architecture that has become quite popular as a model for both human and machine vision. The first stageof processing involves a set of parallel pathways, eachdevoted to one particular-visual property. We propose that the measurements of these basic properties be con-sidered as the elements of early vision. We think of earlyvision as measuring the amounts of various kinds of vi-sual "substances" present in the image (e.g., redness orrightward motion energy). In other words, we are inter- ested in how early vision measures “stuff” rather than in how it labels “things.”What, then, are these elementary visual substances?Various lists have been compiled using a mixture of intui-tion and experiment. Electrophysiologists have describedneurons in striate cortex that are selectively sensitive tocertain visual properties; for reviews, see Hubel (1988) and DeValois and DeValois (1988). Psychophysicists haveinferred the existence of channels that are tuned for cer- tain visual properties; for reviews, see Graham (1989), Olzak and Thomas (1986), Pokorny and Smith (1986), and Watson (1986). Researchers in perception have foundaspects of visual stimuli that are processed pre-attentive- ly (Beck, 1966; Bergen & Julesz, 1983; Julesz & Bergen,

Multidimensional orientation estimation with applications to texture analysis and optical flow

Abstract: The problem of detection of orientation in finite dimensional Euclidean spaces is solved in the least squares sense. The theory is developed for the case when such orientation computations are necessary at all local neighborhoods of the n-dimensional Euclidean space. Detection of orientation is shown to correspond to fitting an axis or a plane to the Fourier transform of an n-dimensional structure. The solution of this problem is related to the solution of a well-known matrix eigenvalue problem. The computations can be performed in the spatial domain without actually doing a Fourier transformation. Along with the orientation estimate, a certainty measure, based on the error of the fit, is proposed. Two applications in image analysis are considered: texture segmentation and optical flow. The theory is verified by experiments which confirm accurate orientation estimates and reliable certainty measures in the presence of noise. The comparative results indicate that the theory produces algorithms computing robust texture features as well as optical flow. >

Method for facilitating dental diagnosis and treatment

Abstract: A method for use in forming a preparation in a patient's jaw comprises the steps of (a) generating electrically encoded data specifying pre-existing dental structure in the patient's jaw, (b) transmitting the data to a computer, (c) operating the computer to generate, on a monitor connected to the computer, a graphic representation of the pre-existing structure, (d) further operating the computer to predetermine an optimal position and an optimal orientation of a material removal tool with respect to the pre-existing structure, and (e) additionally operating the computer to generate, on the monitor, a graphic representation of the tool in the optimal position and the optimal orientation relative to the pre-existing structure. The method may be used to conduct a practice operation on the patient. In such a practice operation, the dental practitioner orients a dental type instrument (e.g., a probe or a drill) in juxtaposition to the pre-existing structure at the optimal position (shown on the monitor). The computer is provided with electrical feedback or signals as to the actual position and the actual orientation of the instrument. The computer is then operated to automatically determine an angle between the optimal orientation and the actual orientation. The computer then alerts the dental practitioner as to the deviation, if any, between the instrument and the optimal position and orientation thereof.

Computer aided drawing in three dimensions

Abstract: A computer system for aiding in the design of an object, comprising a first sensor representing the object and adapted to be moved in three dimensions in a work area by a designer, the first sensor providing signals to the computer system that indicate its position and orientation in the work area, and a second sensor adapted to be moved by the designer in three dimensions in the work area, the second sensor providing signals to the computer system that indicate its position and orientation in the work area; the computer system responds to the signals from the first and second sensors by creating a displayed image corresponding to a three-dimensional model of the object in a virtual work area that corresponds to the designer's work area, the model comprising lines that each have a shape and position that corresponds to movement by the designer of at least one of the sensors, and by controlling the position and orientation of the model in the virtual work area in accordance with the motion of at least one of the sensors

Stereoscopic X-ray fluoroscopy system using radiofrequency fields

Abstract: During an X-ray procedure, the position and orientation of an invasive device, such as a catheter are measured with radio frequency fields and displayed stereoscopically. Instantaneous three-dimensional positions of the invasive device are displayed by superposition of a graphic symbol on static X-ray images obtained at two different view angles. The X-ray images are obtained only when deemed necessary by the operator to minimize X-ray dose. A single X-ray source and detector may be implemented since it is not necessary to obtain the X-ray images simultaneously.

Weighted selection of image features for resolved rate visual feedback control

Abstract: The authors develop methodologies for the automatic selection of image features to be used to visually control the relative position and orientation (pose) between the end-effector of an eye-in-hand robot and a workpiece. A resolved motion rate control scheme is used to update the robot's pose based on the position of three features in the camera's image. The selection of these three features depends on a blend of image recognition and control criteria. The image recognition criteria include feature robustness, completeness, cost of feature extraction, and feature uniqueness. The control criteria include system observability, controllability, and sensitivity. A weighted criteria function is used to select the combination of image features that provides the best control of the end-effector of a general six-degrees-of-freedom manipulator. Both computer simulations and laboratory experiments on a PUMA robot arm were conducted to verify the performance of the feature-selection criteria. >

Eye tracking method and apparatus

Abstract: In applications where it is desired to determine the locations of image features, such as eye monitoring to determine the direction that a person is gazing, determining the point at which he is gazing, or measuring the motions of his eye using a camera to capture an optical image of the eye and image processing to extract information about the eye's gaze point and/or orientation, there is provided a method and apparatus for precise location of image features such as edge coordinates between the pupil anc iris of the eye and of the center coordinates of light reflections off the cornea of the eye.

Noise reduction system

Abstract: A technique is provided to remove noise from images and to enhance their visual appearance through the utilization of a technique which converts an image into a set of coefficients in a multi-scale image decomposition process, followed by modification of each coefficient based on its value and the value of coefficients of related orientation, position, or scale, which is in turn followed by a reconstruction or synthesis process to generate the enhanced image. Also contributing to the improved enhancement is a set of orientation tuned filters of a specialized design to permit steering, with the analysis and synthesis filters also having a self-inverting characteristic. Additionally, steerable pyramid architecture is used for image enhancement for the first time, with the steering being provided by the above orientation tuned filters. The utilization of related coefficients permits coefficient modification with multipliers derived through a statistical or neural-network analysis of coefficients derived through the utilization of clean and degraded images, with the modifiers corresponding to vectors which result in translating the degraded image coefficients into clean image coefficients, in essence by cancelling those portions of a coefficient due to noise. Further improvements include an overlay of classical coring on single coefficients. Thus, the subject technique provides improved image enhancement through the use of a multi-band or scale-oriented analysis and synthesis transform having improved coefficient modification, good orientation tuning, improved bandpass characteristics, and good spatial localization.

Scale space approach to directional analysis of images.

Abstract: In this paper a new technique for directional analysis of linear patterns in images is proposed based on the notion of scale space. A given image is preprocessed by a sequence of filters which are second derivatives of 2-D Gaussian functions with different scales. This gives a set of zero crossing maps (the scale space) from which a stability map is generated. Significant linear patterns are detected from measurements on the stability map. Information regarding orientation of the linear patterns in the image and the area covered by the patterns in specific directions is then computed. The performance of the method is illustrated through applications to synthetic patters and to scanning electron microscope images of collagen fibrils in rabbit ligaments.

An object position and orientation IC with embedded imager

Abstract: A CMOS VLSI chip that determines the position and orientation of an object against a dark background is described. The chip operates in a continuous-time analog fashion, with a response time as short as 200 mu s and power consumption under 50 mW. A self-contained phototransistor array acquires the image directly, and the output is a set of eight currents from which the position and orientation can be found. The output can be sampled at up to 5000 frames/s, and there is a greatly reduced analog-digital (A-D) conversion requirement (per frame) for real-time interfacing with a digital system. Orientation is determined to within +or-2 degrees or better for moderately sized and sufficiently elongated objects. Chip dimensions are 7900 mu m*9200 mu m. >

Fast shape from shading

Abstract: Extracting surface orientation and surface depth from a shaded image is one of the classic problems in computer vision. Many previous algorithms either violate integrability, i.e., the surface normals do not correspond to a feasible surface, or use regularization, which biases the solution away from the true answer. A recent iterative algorithm proposed by Horn overcomes both of these limitations but converges slowly. This paper uses a new algorithm, hierarchical basis conjugate gradient descent, to provide a faster solution to the shape from shading problem. This approach is similar to the multigrid techniques that have previously been used to speed convergence, but it does not require heuristic approximations to the true irradiance equation. The paper compares the accuracy and the convergence rates of the new techniques to previous algorithms.

Relative orientation revisited

Abstract: Relative orientation is the recovery of the position and orientation of one imaging system relative to another from correspondences among five or more ray pairs. It is one of four core problems in photogrammetry and is of central importance in binocular stereo as well as in long-range motion vision. While five ray correspondences are sufficient to yield a finite number of solutions, more than five correspondences are used in practice to ensure an accurate solution with least-squares methods. Most iterative schemes for minimizing the sum of the squares of weighted errors require a good guess as a starting value. The author has previously published a method that results in the best solution without requiring an initial guess [ J. Opt. Soc. Am. A4, 629 ( 1987)] An even simpler method is presented here that utilizes the representation of rotations by unit quaternions.

A statistical analysis of natural images matches psychophysically derived orientation tuning curves.

Abstract: A neural net method is used to extract principal components from real-world images. The initial components are a Gaussian followed by horizontal and vertical operators, starting with the first derivative and moving to successively higher orders. Two of the components are 'bar-detectors'. Their measured orientation selectivity is similar to that suggested by Foster & Ward (Proc. R. Soc. Lond. B 243, 75 (1991] to account for brief-exposure psychophysical data. In tests with noise images, the ratio of sensitivity between the two components is controlled by the degree of anisotropy in the image.

Rectilinear object image matcher

Abstract: A process for extracting the precise perimeter of buildings from down-looking terrain images. The process works for any rectilinear building shape, and no restrictions are placed on the orientation or scale of the buildings within an image. The process has the advantages of robustness and execution speed. The process is robust in that it can extract building perimeters from a digitized image in the presence of multiple noise sources. The execution speed is proportional to N+M, where the size of the image is N by M pixels.

Fast evaluation of patient set-up during radiotherapy by aligning features in portal and simulator images.

Abstract: A new fast method is presented for the quantification of patient set-up errors during radiotherapy with external photon beams. The set-up errors are described as deviations in relative position and orientation of specified anatomical structures relative to specified field shaping devices. These deviations are determined from parameters of the image transformations that make their features in a portal image align with the corresponding features in a simulator image. Knowledge of some set-up parameters during treatment simulation is required. The method does not require accurate knowledge about the position of the portal imaging device as long as the positions of some of the field shaping devices are verified independently during treatment. By applying this method, deviations in a pelvic phantom set-up can be measured with a precision of 2 mm within 1 minute. Theoretical considerations and experiments have shown that the method is not applicable when there are out-of-plane rotations larger than 2 degrees or translations larger than 1 cm. Inter-observer variability proved to be a source of large systematic errors, which could be reduced by offering a precise protocol for the feature alignment.

Adaptive Multidimensional Filtering

Abstract: This thesis contains a presentation and an analysis of adaptive filtering strategies for multidimensional data. The size, shape and orientation of the flter are signal controlled and thus adapted locally to each neighbourhood according to a predefined model. The filter is constructed as a linear weighting of fixed oriented bandpass filters having the same shape but different orientations. The adaptive filtering methods have been tested on both real data and synthesized test data in 2D, e.g. still images, 3D, e.g. image sequences or volumes, with good results. In 4D, e.g. volume sequences, the algorithm is given in its mathematical form. The weighting coefficients are given by the inner products of a tensor representing the local structure of the data and the tensors representing the orientation of the filters. The procedure and lter design in estimating the representation tensor are described. In 2D, the tensor contains information about the local energy, the optimal orientation and a certainty of the orientation. In 3D, the information in the tensor is the energy, the normal to the best ftting local plane and the tangent to the best fitting line, and certainties of these orientations. In the case of time sequences, a quantitative comparison of the proposed method and other (optical flow) algorithms is presented. The estimation of control information is made in different scales. There are two main reasons for this. A single filter has a particular limited pass band which may or may not be tuned to the different sized objects to describe. Second, size or scale is a descriptive feature in its own right. All of this requires the integration of measurements from different scales. The increasing interest in wavelet theory supports the idea that a multiresolution approach is necessary. Hence the resulting adaptive filter will adapt also in size and to different orientations in different scales.

Accurate parameter estimation of quadratic curves from grey-level images

Abstract: Accurate estimation of the parameters of a curve present in a grey-level image is required in various machine-vision and computer-vision problems. Quadratic curves are more common than other curve types in these fields. The accuracy of the estimated parameters depends not only on the global interpolation technique used, but, as well, on compensation of major sources of error. In this paper, first, as a preliminary step in accurate parameter estimation of quadratic curves, a sequential distortion-compensation procedure is formulated. This procedure addresses the major distortion factors involved in the transformation of a curve from the object space to the image space. Subsequently, as a means for accurate estimation of the coordinates of edge points, a new subpixel edge detector based on the principle of the sample-moment-preserving transform (SMPT) is developed. A circular-arc geometry is assumed for the boundary inside the detection area. The new arc-edge detector is designed as a cascade process using a linear-edge detector and a look-up table. Its performance is compared with that of a linear subpixel edge detector. Then, as a part of the main theme of the paper, the estimation of the five basic parameters of an elliptical shape based on its edge-point data is addressed. To achieve the desired degree of accuracy, a new error function is introduced and as the basis for a comparative study, an objective and independent measure for “goodness” of fit is derived. The proposed new error function and two other error functions previously developed are applied to six different situations. The comparative performance of these error functions is discussed. Finally, as the basis for evaluation of the total process, a 3D location estimation problem is considered. The objective is to accurately estimate the orientation and position in 3D of a set of circular features. The experimental results obtained are significant in two separate ways: in general, they show the validity of the overall process introduced here in the accurate estimation of 3D location; in particular, they demonstrate the effectiveness of the sub-pixel edge detector and the global interpolation technique, both developed here.

Determining 3-D object pose using the complex extended Gaussian image

Abstract: A method based on the extended Gaussian image (EGI) which can be used to determine the pose of a 3-D object is presented. In this scheme, the weight associated with each outward surface normal is a complex weight. The normal distance of the surface from the predefined origin is encoded as the phase of the weight, while the magnitude of the weight is the visible area of the surface. This approach decouples the orientation and translation determination into two distinct least-squares problems. Experiments involving synthetic data of two polyhedral and two smooth objects as well as real range data of the same smooth objects indicate the feasibility of this method. >

Automated video imagery database generation using photogrammetry

Abstract: A method for converting forward looking video or motion picture imagery into a downlooking database suitable for use in an image generation system to generate realtime perspective images for simulation purposes. A digital video camera photographs a sequence of forward looking frames along a course including several known ground control points. Digital data from the digital video camera is read into a computer. The initial position and the position of ground control points is read into the computer. A Kalman filter technique provides continuous estimates of exact camera location in x, y, z coordinates, and in roll, pitch and yaw orientation. A correlation filter determines corresponding pixels in adjacent frames. Range from the camera to the pixel surfaces is calculated to determine the x, y and z position thereof. A modified mathematical stereophotogrammetry technique is used. Radiometric data and elevation data is extracted from the lower portion of the frame for each pixel. After the radiometric and elevation data have been established for each pixel in each frame, the imagery is warped onto the elevation data to generate a top down view. The database is then ready for use in an image generation system.

Towards an autonomous system for orienting digital stereopairs

Abstract: We present a method to automatically compute the orientation of digital stereopairs. The system that we developed is based on feature-baded, hierarchical matching combined with precise point determination. We use the LoG operator to determine zero crossings which we then match in the ψ-s domain. No assumptions are required because the ψ-s representation is rotation and scale invariant. In order to obtain maximum possible accuracy for corresponding points, a precise point matching scheme is employed. With the approximations obtained from matching zero crossings, corresponding points with sub-pixel accuracy are determined by using the Forstner interest operator combined with area correlation.

Multidimensional orientation : texture analysis and optical flow

Abstract: Keywords: LTS1 Reference LTS-CONF-1991-012 Record created on 2006-06-14, modified on 2016-08-08

Manipulable three-dimensional projection imaging method

Abstract: A method of developing a foreground image from two views of an object, such as orthogonal x-ray views, for the making of a projectable three-dimension image on a computer display monitor superimposed on a background image. The foreground image can be included on the original view of the object or can be separate therefrom or can be represented by digital mathematical expression. The method finds particular application in medical applications such as brachytherapy dosimetry, breast biopsy localizing, and external dosimetry computation for radiotherapy. When used with a dosimetry application, isodose lines can be computed and imaged for various simulated positioning and orientation of the radiation sources and simulated dose sizes.

The MIT Vision Chip Project: analog VLSI systems for fast image acquisition and early vision processing

Abstract: The goal of the MIT Vision Chip Project is to design and build prototype analog early vision systems that are remarkably low-power, small, and fast. The typical system will perform one or more computation-intensive image-processing tasks at hundreds to thousands of frames per second using only tens to hundreds of milliwatts. The entire system with lens, imager, power supply and support circuitry can fit inside a cigar box. The authors briefly outline the overall project and describe two tested chips in some detail. Particular attention is given to a fast imager and processor chip for object position and orientation, and to an integrated ccd (charge-coupled device) imager and processors for edge detection. >

Horizontal--Vertical Filters in Early Vision Predict Anomalous Line-Orientation Identification Frequencies

Abstract: A characteristic of early visual processing is a reduction in the effective number of filter mechanisms acting in parallel over the visual field. In the detection of a line target differing in orientation from a background of lines, performance with brief displays appears to be determined by just two classes of orientation-sensitive filter, with preferred orientations close to the vertical and horizontal. An orientation signal represented as a linear combination of responses from such filters is shown to provide a quantitative prediction of the probability density function for identifying the perceived orientation of a target line. This prediction was confirmed in an orientation-matching experiment, which showed that the precision of orientation estimates was worst near the vertical and horizontal and best at about 30 degrees each side of the vertical, a result that contrasts with the classical oblique effect in vision, when scrutiny of the image is allowed. A comparison of predicted and observed frequency distributions showed that the hypothesized orientation signal was formed as an opponent combination and horizontal and vertical filter responses.

From voxel to curvature

Abstract: 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. >

Rotation of images for optical character recognition

Abstract: A method and apparatus for properly orienting an text in order to perform optical character recognition (OCR). The text is digitized and placed into an image. The image is subsampled to determine an initial "guess" about the orientation of the image. If there are are specified number of sets of lines between lines having no black-to-white or white-to-black transitions, then the image is assumed to be oriented correctly. Otherwise, the image is assumed to be perpendicular to the line-of-sight of the OCR engine and the image is rotated 90 degrees counterclockwise in a preferred embodiment. A combination of rotations and trial OCR scans for the image is performed until the best results for the trial OCR is obtained or the maximum number of iterations is exceeded. Then, the remainder of OCR is performed on the image.

Continuous automatic vehicle orientation on road - using monocular image and modelling to estimate road curvature and width from geometry and dynamic aspects of scene

Abstract: The method involves using an image generating system and a computerised image processor to produce vehicle control data. The image data of one monocular image of a sequence of images is modelled by orientation with spatially geometrical and temporally dynamic aspects of a scene, using a program-controlled computer. A recursive estimation procedure is used to determine the road parameters, i.e. the predicted horizontal and vertical curve paths, as well as the road width and the characteristic road situation. A complete cycle of the procedure, including the utilisation of the control data, pref. lasts 1/10 to 1/30 of a second. USE/ADVANTAGE - For automatic vehicle guidance. Interprets monocular image data from camera mounted on vehicle, for determination of road course.