Showing papers on "Real image published in 1993"

Omniview motionless camera endoscopy system

Abstract: A endoscopic-type device for omnidirectional image viewing providing electronic pan-and-tilt orientation, rotation, and magnification within a selected field-of-view for use in applications in various environments such as in internal medicine inspection, monitoring, and surgery. The imaging device (using optical or infrared images) is based on the effect that the image from a wide angle lens, which produces a circular image of an entire field-of-view, can be mathematically corrected using high speed electronic circuitry. More specifically, an incoming image from a endoscope image acquisition source, including a wide angle lens, is transmitted through an image conduit and captured by a camera that produces output signals according to that image. A transformation of these output signals is performed for the viewing region of interest and viewing direction, and a corrected image is output as a video image signal for viewing, recording, or analysis. Multiple simultaneous images can be output from a single input image.

Electro-optic vision system which exploits position and attitude

Abstract: The present invention is generally concerned with electronic vision devices and methods, and is specifically concerned with image augmentation in combination with navigation, position, and attitude devices. In the simplest form, devices of the invention can be envisioned to include six major components: A 1) camera to collect optical information about a real scene and present that information as an electronic signal to; a 2) computer processor; a 3) device to measure the position of the camera; and a 4) device to measure the attitude of the camera (direction of the optic axis), thus uniquely identifying the scene being viewed, and thus identifying a location in; a 5) data base where information associated with various scenes is stored, the computer processor combines the data from the camera and the data base and perfects a single image to be presented at; a 6) display whose image is continuously aligned to the real scene as it is viewed by the user. The present invention is a vision system including devices and methods of augmented reality wherein an image of some real scene is altered by a computer processor to include information from a data base having stored information of that scene in a storage location that is identified by the real time position and attitude of the vision system. It is a primary function of the vision system of the invention, and a contrast to the prior art, to present augmented real images and data that is continuously aligned with the real scene as that scene is naturally viewed by the user of the vision system. An augmented image is one that represents a real scene but has deletions, additions and supplements.

Image editing system including masking capability

Abstract: A system and method for editing digital images in three dimensions includes a computer for storing a digital image of an object and a background, as well as at least one additional background image. Based upon the difference between the hues of the edge of the object and the surrounding background and a predetermined hue difference, the computer locates the edge of the object and removes portions of the image (i.e., the background) that are outside the edge. Then, the object can be combined with a preselected one of the other background images so as to form a composite image. Components of the preselected background image are assigned relative positions in the X-Y plane, and are also assigned a value defining their location in one of a plurality of layers which form the Z dimension of the image. The object to be combined with the background is also assigned a value defining its location in at least one of those layers. In another embodiment of the invention, colors of either a digital or video image can be selectively assigned to a mask. The colors can be of the entire image or from a selected area of the image. Color manipulation can then be performed on just the colors of the image defined by the mask. The mask may be used with the entire image, with a selected area of the image, or with objects. Alternatively, the colors of the image defined by an inverted mask are affected by color manipulation.

Towards Quantifying Depth and Size Perception in 3D Virtual Environments

Abstract: With the rapid advance of real-time computer graphics, head-mounted displays HMDs have become popular tools for 3D visualization. One of the most promising and challenging future uses of HMDs, however, is in applications where virtual environments enhance rather than replace real environments. In such applications, a virtual image is superimposed on a real image. The unique problem raised by this superimposition is the difficulty that the human visual system may have in integrating information from these two environments. As a starting point to studying the problem of information integration in see-through environments, we investigate the quantification of depth and size perception of virtual objects relative to real objects in combined real and virtual environments. This starting point leads directly to the important issue of system calibration, which must be completed before perceived depth and sizes are measured. Finally, preliminary experimental results on the perceived depth of spatially nonoverlapping real and virtual objects are presented.

A fast mean-distance-ordered partial codebook search algorithm for image vector quantization

Abstract: A new fast search algorithm for vector quantization using the mean of image vectors is proposed. The codevectors are sorted according to their component means, and the search for the codevector having the minimum Euclidean-distance to a given input vector starts with the one having the minimum mean-distance to it, making use of our observation that the two codevectors are close to each other in most real images. The search is then made to terminate as soon as a simple yet novel test reports that any remaining vector in the codebook should have a larger Euclidean distance. Simulations show that the number of calculations can be reduced to as low as a fourth the number achievable by an algorithm known as the partial distance method. >

On determining the fundamental matrix : analysis of different methods and experimental results

Abstract: The fundamental matrix is a key concept when working with uncalibrated images and multiple viewpoints It contains all the available geometric information and enables to recover the epipolar geometry from uncalibrated perspective views This paper addresses the important problem of its robust determination given a number of image point correspondences We first define precisely this matrix and show clearly how it is related to the epipolar geometry and to the essential matrix introduced earlier by Longuet-Higgins In particular, we show that this matrix, defined up to a scale factor, must be of rank two Different parametrizations for this matrix are then proposed to take into account these important constraints and linear and non-linear criteria for its estimation are also considered We then clearly show that the linear criterion is unable to express the rank and normalization constraints Using the linear criterion leads definitely to the worst result in the determination of the fundamental matrix Several examples on real images clearly illustrate and validate this important negative result To overcome the major weaknesses of the linear criterion, different non-linear criteria are proposed and analyzed in great detail Extensive experimental work has been performed in order to compare the different methods using a large number of noisy synthetic data and real images In particular, a statistical method based on variation of camera displacements is used to evaluate the stability and convergence properties of each method

Image input device having optical deflection elements for capturing multiple sub-images

Abstract: An image input device (10) is provided in which an optical deflector (32) is positioned to divide the image of an object into a plurality of sub-images and to deflect the sub-images to an image sensor via an imaging lens (20). The images sensed by the image sensor are stored in a memory (90) and combined by an image processor (70) to form a composite image of the object. The optical deflector may have a plurality of optical elements (35), the number of which may be the same as the number of sub-images.

Incremental recognition of pedestrians from image sequences

Abstract: An approach that uses a volume model consisting of cylinders for model-based recognition of pedestrians in real-world images is presented. The human body is represented by a volume model, and medical motion data are used for simulating the movement of walking. This knowledge is exploited to determine the 3-D position, as well as the posture of an observed person. By applying a Kalman filter, the model parameters in consecutive images are incrementally estimated. The approach is tested on real image data. >

Distributed representation and analysis of visual motion

Abstract: The central theme of the thesis is that the failure of image motion algorithms is due primarily to the use of vector fields as a representation for visual motion We argue that the translational vector field representation is inherently impoverished and error-prone Furthermore, there is evidence that a direct optical flow representation scheme is not used by biological systems for motion analysis Instead, we advocate distributed representations of motion, in which the encoding of image plane velocity is implicit As a simple example of this idea, and in consideration of the errors in the flow vectors, we re-cast the traditional optical flow problem as a probabilistic one, modeling the measurement and constraint errors as random variables The resulting framework produces probability distributions of optical flow, allowing proper handling of the uncertainties inherent in the optical flow computation, and facilitating the combination with information from other sources We demonstrate the advantages of this probabilistic approach on a set of examples In order to overcome the temporal aliasing commonly found in time-sampled imagery (eg, video), we develop a probabilistic "coarse-to-fine" algorithm that functions much like a Kalman filter over scale We implement an efficient version of this algorithm and show its success in computing Gaussian distributions of optical flow of both synthetic and real image sequences We then extend the notion of distributed representation to a generalized framework that is capable of representing multiple motions at a point We develop an example representation through a series of modifications of the differential approach to optical flow estimation We show that this example is capable of representing multiple motions at a single image location and we demonstrate its use near occlusion boundaries and on simple synthetic examples containing transparent objects Finally, we show that these distributed representation are effective as models for biological motion representation We show qualitative comparisons of stages of the algorithm with neurons found in mammalian visual systems, suggesting experiments to test the validity of the model We demonstrate that such a model can account quantitatively for a set of psychophysical data on the perception of moving sinusoidal plaid patterns (Copies available exclusively from MIT Libraries, Rm 14-0551, Cambridge, MA 02139-4307 Ph 617-253-5668; Fax 617-253-1690) (Abstract shortened by UMI)

Relative 3-D reconstruction using multiple uncalibrated images

Abstract: It is shown how relative 3-D reconstruction for point correspondence of multiple images from uncalibrated cameras can be achieved through reference points. The original contributions with respect to other related works in the field are a direct global method for relative 3-D reconstruction and a geometrical method to select a correct set of reference points among all image points. Experimental results from both simulated and real image sequences are presented. >

A generalized brightness change model for computing optical flow

Abstract: The authors propose an image motion constraint equation based on a model which allows the brightness of a scene point to vary with time, unlike the case in the brightness constancy model. Using this model, they describe a method for the computation of optical flow and investigate its performance in a variety of conditions involving brightness variations of scene points, due to illumination nonuniformity, light source motion, specular reflection, and/or interreflection. It is shown that in the application of this method, care must be taken in the estimation of image derivatives using finite difference methods to prevent biases in the solution. A simple modification is suggested to overcome the problem. A comparison is made with two other models, including the classical brightness constancy model, through results from experiments with real images. >

Virtual image display having a high efficiency grid beamsplitter

Abstract: An on-axis virtual image display system comprises a s-polarized image source (11), such as a polarized cathode ray tube or a polarized liquid crystal display, which has its s-polarized output image coupled through a relay lens (12) towards a high efficiency grid beamsplitter (20). The grid beamsplitter is employed to reflect the s-polarized image through a quarter wave plate (13) onto a totally reflecting concave mirror (14). The image reflected from the concave mirror is converted to a p-polarized image and passes through the quarter wave plate and the grid beamsplitter, producing a virtual magnified image of the source at the location of a user (22).

Recovering and characterizing image features using an efficient model based approach

Abstract: The development of an efficient model-based approach to detect and characterize precisely important features such as edges, corners and vertices is discussed. The key is to propose some efficient models associated to each of these features directly from the image by searching the parameters of the model that best approximate the observed grey level image intensities. Due to the large amount of time required by a first approach that assumes the blur of the imaging acquisition system to be describable by a 2-D Gaussian filter, different solutions that drastically reduce this computational time are considered and developed. The problem of the initialization phase in the minimization process is considered, and an original and efficient solution is proposed. A large number of experiments involving real images are conducted in order to test and compare the reliability, the robustness, and the efficiency of the proposed approaches. >

Blur identification by residual spectral matching

Abstract: The estimation of the point spread function (PSF) for blur identification, often a necessary first step in the restoration of real images, method is presented. The PSF estimate is chosen from a collection of candidate PSFs, which may be constructed using a parametric model or from experimental measurements. The PSF estimate is selected to provide the best match between the restoration residual power spectrum and its expected value, derived under the assumption that the candidate PSF is equal to the true PSF. Several distance measures were studied to determine which one provides the best match. The a priori knowledge required is the noise variance and the original image spectrum. The estimation of these statistics is discussed, and the sensitivity of the method to the estimates is examined analytically and by simulations. The method successfully identified blurs in both synthetically and optically blurred images. >

Iterative algorithms for twin-image elimination in in-line holography using finite-support constraints

Abstract: The quality of reconstructed images from in-line holograms can be seriously degraded by the linear superposition of twin images having the same information but different foci. Starting from the reconstructed field at the real image plane, we make use of the uncontaminated information contained in the out-of-focus wave (virtual image) outside the in-focus wave (real image) support, together with a finite-support constraint, to form an iterative procedure for twin-image elimination. This algorithm can reconstruct complex objects, provided that they are not recorded in very near-field conditions. For real objects additional constraints can be imposed, extending the algorithm application to very near-field conditions. The algorithm’s convergence properties are studied in both cases, and some examples are shown.

A complete two-plane camera calibration method and experimental comparisons

Abstract: For both 3-D reconstruction and prediction of image coordinates, cameras can be calibrated implicitly without involving their physical parameters. The authors present a two-plane method for such a complete calibration, which models all kinds of lens distortions. First, the modeling is done in a general case without imposing the pinhole constraint. Epipolar curves considering lens distortions are introduced and are found in a closed form. Then, a set of constraints of perspectivity is derived to constrain the modeling process. With these constraints, the camera physical parameters can be related directly to the modeling parameters. Extensive experimental comparisons of the methods with the classic photogrammetric method and Tsai's method relating to the aspects of 3-D measurement, the effect of the number of calibration points, and the prediction of image coordinates, are made using real images from 15 different depth values. >

Alignment by maximisation of mutual information

Abstract: A new information-theoretic approach is presented for fi nding the pose of an object in an image. The technique does not require information about the surface properties of the object, besides its shape, and is robust with respect to variations of illumination. In our derivation, few assumptions are made about the nature of the imaging process. As a result the algorithms are quite general and can foreseeably be used in a wide variety of imaging situations. Experiments are presented that demonstrate the approach registering magnetic resonance (MR) images with computed tomography (CT) images, aligning a complex 3D object model to real scenes including clutter and occlusion, tracking a human head in a video sequence and aligning a view-based 2D object model to real images. The method is based on a formulation of the mutual information between the model and the image called EMMA. As applied here the technique is intensity-based, rather than feature-based. It works well in domains where edge or gradient-magnitude based methods have difficulty, yet it is more robust than traditional correlation. Additionally, it has an efficient implementation that is based on stochastic approximation. Finally, we will describe a number of additional real-world applications that can be solved effi ciently and reliably using EMMA. EMMA can be used in machine learning to find maximally informative projections of high-dimensional data. EMMA can also be used to detect and correct corruption in magnetic resonance images (MRI).

Derivation of studio camera position and motion from the camera image

Abstract: Studio camera position and motion may be derived from the camera image by separating out the background and deriving from a background having a number of areas of hue and/or brightness different from adjacent areas estimates of movement from one image to the next. The initial image is used as a reference and amended with predicted motion value. The amended image is compared with incoming images and the result used to derive translation and scale change information. Once the proportion of the reference image contained in an incoming image falls below a threshold a fresh reference image is adopted.

Optical flow from 1D correlation: Application to a simple time-to-crash detector

Abstract: The authors show that a new technique exploiting 1-D correlation of 2-D or even 1-D patches between successive frames may be sufficient to compute a satisfactory estimation of the optical flow field. The algorithm is well-suited to VLSI implementation. The sparse measurements provided by the technique can be used to compute qualitative properties of the flow for a number of different visual tasks. In particular, a method is described to combine the 1-D correlation technique with a scheme for detecting expansion or rotation (T. Poggio et al., 1991) in a simple algorithm which also suggests interesting biological implications. The algorithm provides a rough estimate of time-to-crash. It was tested on real image sequences. Its performance is discussed and the results are compared to previous approaches. >

On the use of level curves in image analysis

Abstract: A digitized image is viewed as a surface over the xy-plane. The level curves of this surface provide information about edge directions and feature locations. This paper presents algorithms for the extraction of tangent directions and curvatures of these level curves. The tangent direction is determined by a least-squares minimization over the surface normals (calculated for each 2 × 2 pixel neighborhood) in an averaging window. The curvature calculation, unlike most previous work on this topic, does not require a parameterized curve, but works instead directly on the tangents across adjacent level curves. The curvature is found by fitting concentric circles to the tangent directions via least-squares minimization. The stability of these algorithms with respect to noise is studied via controlled tests on computer generated data corrupted by simulated noise. Examples on real images are given which show application of these algorithms for directional enhancement, and feature point detection.

Three-dimensional reconstruction by zooming

Abstract: It is shown that it is possible to infer 3-D information from a set of images taken with a zoom lens. A precise study of the optical properties of such a lens gives two major results: The intersection between the optical axis and the image plane can be independently and accurately determined, and the pin-hole model cannot be used directly for the approximation of such a complex lens system. To explain the optical phenomena occurring during a zoom-lens focal-length change, it is shown that a thick optical model must be considered. Experimental reconstruction results for a set of real images, are given. >

Determining the fundamental matrix with planes: instability and new algorithms

Abstract: The fundamental matrix is a key concept when working with uncalibrated images and multiple viewpoints. It contains all the available geometric information and enables recovery of the epipolar geometry from uncalibrated perspective views. The problem of its determination from points which lie in several planes is discussed. In that case, there is an homography between coordinates of points in the two images. The use of different criteria to compute the homography is investigated. A very simple and important relation between the homography matrices obtained from the observation of planar surfaces and the fundamental matrix is then established. Using simulations and real images to validate this analysis, it is shown that as a first consequence of this relation, the general methods to compute the fundamental matrix are unstable when the points lie close to planes. New algorithms are proposed to exploit this situation through the use of the previous relation. Their performance is compared to the performance of the general algorithm using a large number of noisy synthetic data and real images. >

Detecting moving objects using the rigidity constraint

Abstract: A method for visually detecting moving objects from a moving camera using point correspondences in two orthographic views is described. The method applies a simple structure-from-motion analysis and then identifies those points inconsistent with the interpretation of the scene as a single rigid object. It is effective even when the actual motion parameters cannot be recovered. Demonstrations are presented using point correspondences automatically determined from real image sequences. >

Recovery of moving object masks in an image sequence using local spatiotemporal contextual information

Abstract: Locating moving objects in a scene is a generic task needed in numerous applications. Whenever the viewing system is static, detecting moving objects in the scene simply leads to detecting moving regions in the image plane. We describe an original framework to solve this labeling problem. The framework is based on a statistical regularization approach using spatiotemporal Markov fields. It takes temporal variations of the intensity function as observations and delivers two-symbol label maps. The solution is derived by minimizing an energy function using an iterative deterministic relaxation scheme and it is independent of the size, intensity distribution, motion magnitude, and direction of the image of the moving objects. Experiments carried out on real image sequences depicting outdoor scenes are reported. The computations are local and can be easily parallelized. This motion detection algorithm can also lead to an elementary, straightforward but useful tracking procedure applied at the moving object mask level.

Robust and efficient detection of convex groups

Abstract: An algorithm is presented that finds all convex sets of line segments in an image, such that the length of the line segments account for at least some fixed proportion of the length of the convex hull. This enables the algorithm to find convex groups whose contours are partially occluded or missing due to noise. An expected time analysis of the algorithm's performance is performed, together with experiments on real images that show that the algorithm is efficient and that tell when the groups found are unlikely to occur at random, and are likely to capture the underlying structure of a scene. >

Image observation device

Abstract: An image observation device includes a two-dimensional image display element, a relay optical system for forming a real image of an image displayed on the two-dimensional image display element, an eyepiece optical system for forming a magnified image of the real image and bending the optical axis, and a supporting member for supporting the eyepiece optical system to be located directly before the eyes of the user. This arrangement makes it possible to provide the image observation device which is small in size and high in magnification for observation.

Automated direct patterned-wafer inspection

Abstract: A self-reference technique is developed for detecting the location of defects in repeated pattern wafers and masks. The application area of the proposed method includes inspection of memory chips, shift registers, switch capacitors, CCD arrays, and liquid crystal displays (LCD). Using high resolution spectral estimation algorithms, the proposed technique first extracts the period and structure of repeated patterns from the image to sub-pixel resolution, and then produces a defect-free reference image for making comparison with the actual image. Since the technique acquires all its needed information from a single image, there is no need for a database image, a scaling procedure, or any a-priori knowledge about the repetition period of the patterns. Results of applying the proposed technique to real images from microlithography are presented.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Direction of heading from image deformations

Abstract: A method is proposed to compute the direction of heading from the differential changes in the angles between the projection rays of pairs of point features. These angles, the image deformations, do not depend on viewer rotation. The key problem of separating the effects of rotation from those of translation is solved at the input. Experiments show both the feasibility of the method on real images and the advantages of using deformation rather than optical flow. >