Showing papers on "Image plane published in 1987"

Color-Encoded Structured Light for Rapid Active Ranging

Abstract: In this paper, we discuss a novel strategy for rapid acquisition of the range map of a scene employing color-encoded structured light. This technique offers several potential advantages including increased speed and improved accuracy. In this approach we illuminate the scene with a single encoded grid of colored light stripes. The indexing problem, that of matching a detected image plane stripe with its position in the projection grid, is solved from a knowledge of the color grid encoding. In fact, the possibility exists for the first time to acquire high-resolution range data in real time for modest cost, since only a single projection and single color image are required. Grid to grid alignment problems associated with previous multistripe techniques are eliminated, as is the requirement for dark interstices between grid stripes. Scene illumination is more uniform, simplifying the stripe detection problem, and mechanical difficulties associated with the equipment design are significantly reduced.

Scene Segmentation from Visual Motion Using Global Optimization

Abstract: This paper presents results from computer experiments with an algorithm to perform scene disposition and motion segmentation from visual motion or optic flow. The maximum a posteriori (MAP) criterion is used to formulate what the best segmentation or interpretation of the scene should be, where the scene is assumed to be made up of some fixed number of moving planar surface patches. The Bayesian approach requires, first, specification of prior expectations for the optic flow field, which here is modeled as spatial and temporal Markov random fields; and, secondly, a way of measuring how well the segmentation predicts the measured flow field. The Markov random fields incorporate the physical constraints that objects and their images are probably spatially continuous, and that their images are likely to move quite smoothly across the image plane. To compute the flow predicted by the segmentation, a recent method for reconstructing the motion and orientation of planar surface facets is used. The search for the globally optimal segmentation is performed using simulated annealing.

Correction of spatial distortion in MR imaging: a prerequisite for accurate stereotaxy.

Abstract: With magnetic resonance (MR) imaging, accurate spatial information—critical for effective stereotaxy—demands a homogeneous static field and linear gradients. Inhomogeneities and nonlinearities induced by eddy currents during the pulse sequences distort the images and produce spurious displacements of the stereotactic coordinates in both the x-y plane and the z axis. These errors in position can be assessed by means of two phantoms placed within the stereotactic guidance system—a “two-dimensional phantom” displaying “pincushion” distortion in the image (i.e., x, y) plane, and the “three-dimensional phantom” displaying displacement, warp, and tilt of the image plane itself. The pincushion distortion can be “corrected” (reducing displacements from 5 to 1 −2 mm) by calculations based on modeling the distortion as a fourth order two-dimensional polynomial. Based on these corrected images, errors in the z coordinate and tilt of image planes may be corrected by adjustment of the gradient shimming currents. Such correction not only implements stereotaxy under MR guidance but also provides for the accurate transfer of anatomic/pathologic information between MR and CT images.

Modeling and calibration of a structured light scanner for 3-D robot vision

Abstract: In this report we have used projectivity theory to model the process of structured light scanning for 3D robot vision. The projectivity formalism is used to derive a 4 × 3 transformation matrix that converts points in the image plane into their corresponding 3D world coordinates. Calibration of the scanner consists of computing the coefficient of this matrix by showing to the system a set of lines generated by suitable object edges. We end this paper by showing how the matrix can be used to convert image pixel locations into the world coordinates of the corresponding object points using two different scanning strategies.

Integrated head-up and panel display unit

Abstract: An integrated head-up and panel display system for aircraft cockpits and the like is disclosed. The system utilizes a wavelength-sensitive fold mirror to separate the HUD image and the panel images. The system includes a monochromatic HUD image source for projecting the HUD image toward the fold mirror, and at least one panel display image source for projecting panel imagery toward the fold mirror. The transmission function of the fold mirror is notched at the wavelength of the monochromatic HUD image source. Thus, the fold mirror reflects the HUD image in the direction of the HUD optical combiner which reflects the HUD image to the system exit pupil. The fold mirror is adapted to transmit light in the visible spectra outside the narrow bandwidth of the HUD image source, so that the panel image is transmitted through the fold mirror to a look-down display screen assembly. The screen assembly may be a diffusion screen for providing an image plane at the screen, or an assembly of optical elements for providing a panel image superimposed at the system exit pupil.

Method for determination of 3-D structure in biplane angiography

Abstract: A novel method for determination of 3-D structure in biplane angiography, including determining the distance of a perpendicular line from the focal spots of respective x-ray sources to respective image planes and defining the origin of each biplane image as the point of intersection with the perpendicular line thereto, obtaining two biplane digital images at arbitrary orientations with respect to an object, identifying at least 8 points in both images which correspond to respective points in the object, determining the image coordinates of the 8 or more identified object points in the respective biplane images, constructing a set of linear equations in 8 unknowns based on the image coordinates of the object points and based on the known focal spot to image plane distances for the two biplane images; solving the linear equations to yield the 8 unknowns, which represent the fundamental geometric parameters of the biplane imaging system; using the fundamental parameters to calculate the 3-dimensional positions of the object points identified in the biplane images; and determination of the 3-D positions of the vessel segments between the object points.

Vision-based guidance of an agriculture tractor

Abstract: The ordered structure of agricultural row crops can provide useful guidance information for tractor control. A description of research for coupling a machine vision system and a solid-state camera to derive vehicle guidance parameters for a tractor is presented. Image segmentation is enhanced by optical filtering and controlling light intensity to the image sensor. An analysis of camera location and steering errors that can be determined from the row crops is determined by simulating the geometric relationships between the crop canopy and the image plane.

A Fast Reconstruction Algorthm for Stationary Positron Emission Tomography Based on a Modified EM Algorithm

Abstract: An efficient iterative reconstruction method for positron emission tomography (PET) is presented. The algorithm is basically an enhanced EM (expectation maximization) algorithm with improved frequency response. High-frequency components of the ratio of measured to calculated projections are extracted and are taken into account for the iterative correction of image density in such a way that the correction is performed with a uniform efficiency over the image plane and with a flat frequency response. As a result, the convergence speed is not so sensitive to the image pattern or matrix size as the standard EM algorithm, and nonuniformity of the spatial resolution is significantly improved. Nonnegativity of the reconstructed image is preserved. Simulation studies have been made assuming two PET systems: a scanning PET with ideal sampling and a stationary PET with sparse sampling. In the latter, a "bank array" of detectors is employed to improve the sampling in the object plane. The new algorithm provides satisfactory images by two or three iterations starting from a flat image in either case. The behavior of convergence is monitored by evaluating the root mean square of C(b)-1 where C(b) is the correction factor for pixel b in the EM algorithm. The value decreases rapidly and monotonically with iteration number. Although the theory is not accurate enough to assure the stability of convergence, the algorithm is promising to achieve significant saving in computation compared to the standard EM algorithm.

Method of forming pattern and projection aligner for carrying out the same

Abstract: An area on a photoresist film which is formed on a substrate surface having a topography, is exposed a plurality of times in such a manner that the image plane of a mask pattern is formed at a plurality of positions which are spaced apart from a reference plane in the substrate in the direction of an optical axis, and then the photoresist film is developed to form a resist pattern. According to the above method, the effective focal depth of the projection aligner used is enhanced, and moreover the reduction of the image contrast at the photoresist film is very small by the plural exposure operations. Accordingly, a fine pattern can be formed accurately on the substrate surface having the topography.

Quantitative light microscope using a solid state detector in the primary image plane

Abstract: A solid state microscope for viewing and scanning microscopic objects. The solid state microscope has a light source with a condensor and diffusion filter. A moveable stage is provided to allow X, Y, Z plane displacements in order to scan objects under the microscope. There is an objective to magnify the image of the object and project this image onto a two dimensional solid state image sensor. The solid state image sensor sends signals to an analog-to-digital converter where the signals are digitized and sent to a frame memory. A monitor is used to display the image of the object as stored in frame memory. The present invention can be interfaced with a computer to allow for automatic focusing and scanning of an image. The computer also houses storage means to store images. Methods of scanning an object are also described. A prism element can be used to obtain spectral scans of an object. In another scanning method, a first edge row of pixels is used to detect an object of interest in the scanned image. This first detection row activates an area of the sensor array at a later time to capture the entire image. In this way, only relevant information is collected and processed.

Super-resolution in confocal scanning microscopy

Abstract: In a previous paper, (Bertero et al., Opt. Acta. vol.3., p.923 (1984)), it was shown that the resolution of the type-II confocal scanning microscope may be improved by recording the full image and by inverting the data. In this paper, the authors propose a numerical method which can be easily implemented and, in principle, applied to the practical problem. They show that by using a rather small number of data points on the image plane, it is possible to obtain the improvement in resolution (by a factor of two) predicted in their previous analysis.

Design considerations for holographic optical interconnects.

Abstract: The geometrical design characteristics of multiple-image holograms are evaluated. A figure of merit expressing these characteristics as a function of the hologram diameter and the distance between the hologram and the image plane is developed. This value is then used to compare two designs which are capable of forming several hundred interconnections. The results indicate that these connections can be formed between points on the substrate separated by 2-3 cm provided that the holograms are separated from the substrate plane by 0.5-1 cm. Each hologram design is experimentally demonstrated in bleached photographic emulsions.

Camera rotation invariance of image characteristics

Abstract: The image transformation due to camera rotation relative to a stationary scene is analyzed, and the associated transformation rules of “features” given by weighted averaging of the image are derived by considering infinitesimal generators on the basis of group representation theory. Three-dimensional vectors and tensors are reduced to two-dimensional invariants on the image plane from the viewpoint of projective geometry. Three-dimensional invariants and camera rotation reconstruction are also discussed. The result is applied to the shape recognition problem when camera rotation is involved.

Projected free fall trajectories. I. Theory and simulation

Abstract: How we manage to reconstruct the three-dimensional character of the world from the two-dimensional representations on our retinae has been a lively subject of research in the last ten or fifteen years. One principle that has emerged unifying many of these ideas is the need for constraints to allow the visual system to interpret the images it receives as three-dimensional. These constraints come from assumptions about the nature of the situation that produced the image. We have looked at how gravity can be used as a constraint in the case of a free fall trajectory projected onto an image plane by central projection. We have examined several possible methods for deriving the initial conditions of the trajectory from the two-dimensional projection, and examined their behavior under noisy and noiseless conditions, using both image simulations and videotapes of a real ball. We show that there are several ways to robustly compute the initial conditions of the parabolic trajectory from the image data in the presence of noise.

Method for determining expansion centers and predicting sidelobe levels for circular-harmonic filters

Abstract: A map corresponding to energy of circular-harmonic components developed about every point of the image plane allows the determination of the expansion center that will yield the best correlation intensity and the best discrimination ability for the circular-harmonic filter. The map also allows the prediction of the location and of the maximum values of sidelobes. This method is much faster than previous methods for finding proper centers, and it yields more information.

Apparatus and method for monochrome/multicolor display and superimposed images

Abstract: A multicolor display system includes a graphics display controller (45) for selectively generating bit patterns of pixel data for a plurality of images for display; a plurality of memories (47), (49), (51) for storing the bit patterns for each image respectively, and for establishing a plurality of individual memory planes (47), (49), (51) each associated with particular ones of the images; a color look-up table (127) coupled to the memories for receiving the bit patterns therefrom and selectively establishing a color priority hierarchy amongst the associated image planes, for providing for display only the pixel data bits associated with the highest priority image plane at display locations or pixel points where the images of two or more image planes intersect; and D/A converters (75) for converting the pixel data bits for each memory plane from the look-up table to analog signals for connection to a display device.

Camera image plane size control device

Abstract: Apparatus is provided for controlling the size of the image plane in a camera having a zoom lens. The apparatus includes one or more aperture frames (31, 32, 120) which define the image plane size, and an actuator which is adapted to move the aperture frame or frames along the film plane in accordance with the optical position of the exit pupil of a zoom lens. Two frames can be moved in opposite directions over an equal displacement. Further, a single frame (120) can be moved along the optical lens axis in order to ensure that the film remains substantially flat during photography, and is moved away from the film path during film winding and unwinding operations. Additionally, the frame can be provided with projecting portions along opposite side edges of a central aperture in order to control the image plane size.

Direct finger reading

Abstract: The technique for optically scanning a finger to produce a fingerprint image involves positioning the finger surface to be optically scanned so that it is exposed and, in particular, is not pressed against a platen. A slit light beam along the length of the forward part of the finger is circumferentially rotated about an axis about the nominal center of the finger. A reflected slit light beam carries modulation information which is focused on a linear array of photo-electric transducers to provide the fingerprint image. The interrogating light is coherent, substantially collimated, light. The plane of the interrogating slit light beam and the plane of the reflected modulated slit light beam are coplanar thereby establishing an illumination plane. The illumination plane is parallel to the axis of the finger and is rotated about that axis during the interrogating scan. The illumination plane is slightly offset from that rotational axis and the incident light in the illumination plane impinges on the finger surface at a slight off-normal axis. This offset and off-normal incidence creates two dimensional shadowing. The finger surface being interrogated is positioned slightly off of the object plane for the downstream focusing optics thereby creating a constructive and destructive interference effect at the image plane defined by the transducers.

An Edge Detection Algorithm for Attenuation Correction in Emission CT

Abstract: A new body edge detection algorithm is presented for attenuation compensation based on calculation in emission computed tomography. Based on the differential geometry, the edge contour on the image plane can be calculated directly from the edge detected on the projection data. A new algorithm is; (1) detect edge contour on projection data, (2) smooth noisy contour by retaining lower order Fourier coefficients and (3) transform it to the edge contour on the image. Manipulation of two dimensional array is only needed in step (1) and the rest can be done by manipulation of one dimensional array. Robustness of the algorithm was tested on the threshold level and number of Fourier coefficients. The algorithm was applied to positron emission computed tomography. It can be applied to single photon emission computed tomography as well.

Charge-Coupled Computing For Focal Plane Image Preprocessing

Abstract: A new class of charge-coupled devices called charge-coupled-computing devices is described. These analog circuits perform arithmetic functions such as addition, subtraction, and magnitude comparison in the charge domain. The circuits are compact and are designed to be insensitive to rail voltages, simplifying their utilization. These devices, in conjunction with input, output, and analog memory circuits, can be combined to form a simple but general-purpose and fully programmable charge-coupled computer. A prototype charge-coupled computer has been fabricated and tested. Prospects for forming a large array of computers (e.g., 1000 to 10,000) on a single chip for spatially parallel image preprocessing are discussed. Such image plane preprocessing of data would find use in real-time mobile robot vision systems, in which low power, lightweight computing is critical for economical viability.

Three-dimensional electro-optical tracker

Abstract: Improved performance in an electro-optical tracker is achieved by incorporating range measurements. Further, the tracker uses a Kalman filter in which the target is modeled as the superposition of two Gaussian ellipsoids in space and projected onto an image plane.

Solid-state image pickup device

Abstract: PURPOSE:To operate a device with low cost and low power consumption and without being equipped with a mechanical moving part and to reduce the effect of aberration remarkably by arranging a light deflector in the parallel light flux of an afocal image forming optical system between the focal plane of a photographing lens and a solid- state image pickup element. CONSTITUTION:An afocal image forming system is constituted between the image plane of the photographing lens and the solid-stage image pickup element and in its parallel optical path, the first optical member 1 consisting of a laminated structure in which a liquid crystal layer 11, a photoconductive film 16 and a dielectric mirror 14 are included is inserted. On the photoconductive film 16 of the first optical member 1, the distribution of the refractive index of the crystal layer 11 with in the first optical member 1 is constituted so that it can be changed linearly and spacially and also its inclination can be changed by the second optical member 2 which generates light intensity distribution having a linear inclination spacially and a means which can change the inclination of the light intensity distribution. The parallel light flux passing through the crystal layer, by the change of its advancing direction by the means and the change of its image forming position within an image forming plane, can generate the vibration of an image.

Closed-loop recursive estimation of 3D features for a mobile vision system

Abstract: This paper presents a scheme allowing to estimate parameters which describe geometrical structures in a 3D scene by only using informations issued from a sequence of images provided by a mobile vision sensor with known motion. We first recall the basic used models : points and lines, and then relate their perspective projection in the image plane to the camera motion. Some techniques of recursive filtering are used into the sequence of images to incrementaly build the 3D scene all along the displacement of the camera. Some experimental results in the field of robotics are given.

Fast Magnetic Resonance Imaging with Simultaneously Oscillating and Rotating Fiell Gradients

Abstract: We present an approach to magnetic resonance imaging employing a magnetic field gradient that rotates 180 degrees in the image plane while the gradient magnitude oscillates rapidly during the rotation. A single free induction decay recorded during this rotation contains all the information needed to reconstruct a two-dimensional image. In effect, each sinusoidal oscillation of the gradient provides information corresponding to one projection in more conventional Fourier-projection approaches. Since the data acquisition can be achieved in a period less than T2, the method offers the potential of great speed, which is limited only by the gradient modulation frequency. An explicit image reconstruction formula is derived that gives, when evaluated, a reconstruction of the magnetization equal to the true magnetization convolved with a space-invariant point spread function. This point spread function is derived and characterizes the resolving power and sidelobe response of the technique. Moreover, we derive a similar reconstruction formula which is valid when known inhomogeneities in the static field H0 and T2 are present. Finally, we show how the general approach can be extended to three dimensions.

Light scanning system

Abstract: A light scanning system employing a rotating mirror, spherical lens, and a toric-surfaced reflecting mirror. The toric-surfaced reflecting mirror is disposed in the optical path between the spherical lens and the image plane. The spherical lens sufficiently corrects field curvature and the toric-surfaced reflecting mirror corrects scan nonlinearity. And by the spherical lens and the toric-surfaced reflecting mirror together, the field curvature and the scan nonlinearity are satisfactorily corrected. The toric-surfaced reflecting mirror is surfaced to have a circular arc with a larger radius of curvature in the scan plane and to have a circular arc with a smaller radius of curvature in the cross-scan plane.

Projection optical apparatus for mask to substrate alignment

Abstract: The projection optical apparatus includes light-emitting means which are disposed on a stage movable along the image plane in the projection optical apparatus and which define a light-emitting plane having a predetermined shape; photoelectric detection means which is disposed at a position substantially in conjugate relationship with a pupil of said projection optical apparatus and which receives the light emitted from the light-emitting plane of the light-emitting means through the projection optical system and a mask in which a pattern is defined at a predetermined position; and position detection means which controls the stage in such a way that the image projected on the light-emitting plane is shifted in relation to the mask pattern and which detects the superposed position between the image and the pattern in response to the light signal derived from the photoelectric detection means while the projected image is shifted and to the position of the stage.

Device for detecting a magnification error in an optical imaging system

Abstract: A device is described for detecting a magnifi­cation error in an optical imaging system comprising a lens system (L₁, L₂) which is telecentric at one side. Two gratings (RG₁, RG₂) arranged in the object plane (MA) are imaged onto two gratings (WG₁, WG₂) arranged in the image plane (W; WT) and the radiation beams (b₁, b₂) by means of which these images are formed are incident on two radiation-sensitive detection systems (D₁, D₂) which supply periodic signals (S₁, S₂). By phase comparison of these signals a magnification error (S ME ) and, if desired, a focussing error can be measured very accurately.

A new development in camera calibration: calibrating a pair of mobile cameras

Abstract: A new method of camera calibration is proposed for active visual sensing for use in three-dimensional (3D) scene analysis. The method permits calibration of a mobile camera as a function of the position and orientation of the camera. The algorithm for identification of the calibration matrices is divided into two steps: first, calibration for a fixed position of the camera (i. e. , the transformation between the real-world coordinates and the coordinates of the corresponding points in the image plane of the camera); second, calibration as a function of the position and orientation of the camera, which uses the prior information of the calibration for a fixed position. The method can be used for any mobile camera as long as the movement of the camera support is known.

Imaging method and apparatus for electron microscopes

Abstract: A transmission electron microscope is disclosed, having an electron-energy spectrometer, a first imaging stage of four electron lenses in front of the spectrometer, and a second imaging stage of two more electron lenses following the spectrometer. The parts are so arranged, according to the disclosed structure, and so operated, according to the disclosed method, that a large range of magnifications can be obtained while the object or specimen to be examined remains in a fixed location, without having to refocus when the magnification is changed. The change in magnification occurs by changing the operation of the first imaging stage. The second imaging stage operates at a substantially fixed magnification, its magnification being changed, if at all, only to accommodate the size of the output image from the second stage to size of the available working area of the detector in the final image plane (fluorescent screen, photographic film, or electronic detector). The first stage, at all magnifications, always images the object or an image of a diffraction pattern of the object into the input image plane of the spectrometer and an image of the electron source into the input crossover plane of the spectrometer. The spectrometer is of the prism-mirror-prism type, and improved results are obtained by making the entrance and exit surfaces of the prism curved rather than planar.