Showing papers on "Spatial filter published in 1987"

Method and system for high-speed, 3-d imaging of an object at a vision station

Abstract: A method and system for high-speed, 3-D imaging of an object at a vision station including a flying spot laser scanner, a dynamically configurable spatial filter and a diffuser for spatial averaging, are used in conjunction with a variable transmission filter in an optical depth sensing system. The reflected laser signal received by the sensing system is first spatially filtered and averaged and then split into first and second beams which are imaged onto a pair of highly sensitive photodetectors which introduce capability for high-speed, 3-D sensing under low light level conditions. The first beam passes through a variable transmission filter which is used to encode position which, in turn, is proportional to the height of the object. The second or reference split beam is provided to compensate for changes in the reflectance of the object and the power of the laser scanner. A high-speed signal processing unit which incorporates special circuitry to greatly extend dynamic range computes the ratio of the transmitted signal to the sum of the reference signal and the transmitted signal to determine height information. The signal processing unit also contains noise rejection circuitry which is activated during "off" and "on" periods of laser diode TTL modulation and includes feedback control for pulse amplitude modulation of the laser diode source if necessary to increase dynamic range of the system.

Spatial Filtering of Noninvasive Multielectrode EMG: Part I-Introduction to Measuring Technique and Applications

Abstract: Complementary to its conventional applications, surface EMG is also suited to gain more detailed information on the functional state of a muscle, when measurement configurations with smaller pickup areas are used. A new category of suitable measurement configurations is obtained by application of the spatial filtering principle to electromyography. In a spatial filter unit, the signals of several recording electrodes are combined to form one output signal channel. The filter characteristic is determined by the weighting factors used and by the geometrical arrangement of the electrodes. Extended multielectrode arrays and multichannel recording make possible the detection of correlated excitations at different sites of the muscle. Even in high levels of muscle contraction, single motor unit impulses that are suitably shaped by filtering can be repeatedly recognized in the surface EMG signal. In clinical studies, pathologically shaped impulses have been identified indicating multiple innervation zones. The initiation and the propagation of excitation within single motor units can be detected with improved accuracy even from very small muscles.

Spatial Filtering of Noninvasive Multielectrode EMG: Part II-Filter Performance in Theory and Modeling

Abstract: Spatial filtering, particularly common in the field of engineering, is adapted in theory and practice to the filtering of propagating spatial EMG signals. This technique offers a new flexibility in the design of selective EMG measurement configurations. Longitudinal as well as two-dimensional spatial filters can be used. The conditions for the design of suitable spatial filters are deduced by signal theory. The performances of different selected configurations are compared by means of a given simple model of an excited motor unit. The modeling results compare well to the previously described experimental signals.

Application of spheroidal sequences to array processing

Abstract: Eigenvector methods for narrow-band source location are based upon the key assumption that the spatial correlation matrix of the noise field is known. Unfortunately, these methods are very sensitive to errors upon it. This paper describes a method which performs a spatial filtering using discrete spheroidal sequences, before applying eigenvector methods. Thus, narrow spatial sectors are selected in which the noise field is easily modeled. In case of large arrays, the proposed method yields resolution properties far superior to the MUSIC technique with known noise correlation.

Principles and development of spatial filtering velocimetry

Abstract: As one of the interesting optical techniques for measurements of the velocity, the spatial-filtering method is treated briefly in this review. The basic theory of the method is examined by analyzing the filtering characteristics of a spatial filter using the power spectral density function. The signal analyses are summarized as one of the techniques used in the spatial filtering method. Various configurations of the spatial filtering velocimeter are classified into typical four groups and outlined according to a variety of spatial filters employed in the velocimeters.

Optical Computing And Image Processing With Ferroelectric Liquid Crystals

Abstract: High-contrast, submicrosecond switching ferroelectric liquid crystal spatial light modulators have many applications to optical computing and image processing. In this paper we describe the use of these low-voltage, low-power, and bistable devices to perform a variety of functions including polarization- and intensity-based logic gates, input/output displays, optical crossbars, and spatial filtering masks.

Arrangement for optical image processing

Abstract: For electro-optical image conversion as well as for optical image processing by spatial filtering, a two-dimensional optical filter is provided which comprises a microstructured grid, the openings of which are designed as a matrix of windows, the windows being provided with electrostatically movable thin-film closures. The window openings are controlled by electrostatic charges which are provided by an electron beam. This matrix of light valves can preferably be used as a electro-optical converter as well as a Fourier filter in an optical computer.

Spatial filtering logic based on polarization

Abstract: A spatial filtering method is presented which can perform binary logic operations for 2-D data arrays. The logic states are characterized by the state of polarization. This approach performs logic without loss of light. Laboratory experiments are described, and experimental results are shown.

Optical Information Processing With The Double Phase Conjugate Mirror

Abstract: The operation of the double phase conjugate mirror (DPCM) is described. It can be regarded as a bidirectional spatial light modulator and controllable filter. Two independent image-bearing beams that may be derived from different lasers exchange their spatial information as they are coupled into each other in a photorefractive crystal. The,DPCM is also shown to be an optical thresholder and spatial filtering device, displaying edge enhancement. We propose the use of a resonator with two facing DPCMs to implement iterative image processing algorithms.

Computer generated hologram recording using a laser printer

Abstract: The use of a laser printer for recording various types of computer generated holograms is discussed, and initial results are presented.

Method and equipment for detecting foreign matter

Abstract: PURPOSE: To extract only foreign matter information without extremely damaging foreign matter scattering light, by illuminating a wafer from an oblique upper part with a rotation angle wherein reflected diffraction light in the directions of x-axis and y-axis does not enter an objective. CONSTITUTION: A wafer 1 is so arranged that two principal pairs of line edge group constituting a circuit pattern 2 on the wafer 1 become parallel to x-axis and y-axis, respectively. When the wafer is illuminated from an oblique upper part at rotation angles of 45° with respect to x-axis and y-axis, the reflected diffraction light from the line edge group parallel to x-axis and y-axis does not enter an objective 7, so that pattern information is eliminated. The line edge group among the pattern 2 with angles of 45° with repect to x-axis and y-axis becomes vertical to laser beam, so that the reflected diffraction light constitutes a Fourier transform image on a Fourier transform plane 11. By arranging a spatial filter 10 on the transform plane 11, the pattern information is eliminated. Thereby extracting foreign matter information only. COPYRIGHT: (C)1989,JPO&Japio

Optical preprocessing using liquid crystal televisions.

Abstract: The suitability of a low-cost liquid crystal TV to function as a spatial light modulator in an optical preprocessor for an electronic pattern recognition system is investigated. The application presented is optical edge enhancement. The liquid crystal TV performs reasonably well where high-quality images are not required. Three optical edge enhancement methods are presented: spatial filtering; image cancellation; and phase cancellation. The phase cancellation method was discovered during the course of this research.

Binary logic by spatial filtering

Abstract: Spatial filtering is one of the main assets of optics for information processing. In this paper we review spatial filtering methods for performing binary logic operations. Many pairs of bits can be processed simultaneously. The input data are arranged in matrix form. The type of operation is usually homogeneous across the matrix. The input is characterized as a diffracting, as a scattering, or as a birefringent structure. Experimental results are shown. Applications of the described method for an optical adder are presented.

Superresolution by incoherent-to-coherent conversion

Abstract: A technique is described whereby resolution many times the Rayleigh limit is achieved by the use of incoherent-illumination interferometry. An object and an imaging system are in one interferometer branch, and a duplicate, dummy system is in the other. The resolution is determined by the aperture of the dummy system and by the size of the source.

Noncoherent-object hologram: its reconstruction and optical processing

Abstract: Encoding a complex-amplitude diffraction pattern on a photographic film by addirtg a suitably chosen coherent reference beam forms a conventional hologram. A hologram of a spatially noncoherent object, referred to as a Γ hologram in this paper, is formed by encoding the complex-valued spatial-coherence function on a square-law detector such as photographic film. This record is made possible by means of a self-refetencing interferometer. Such a record behaves much as a hologram does; it permits reconstruction of the original object by illuminating it with a spatially noncoherent planar source of uniform (constant) intensity. If a conventional coherent-light setup is used with a Γ hologram, the intensity distribution of the reconstruction equals the square of the intensity of the original object. In the research reported in this paper, optical processing of spatially noncoherent objects is accomplished by using and modifying the spatial-coherence function. The Γ hologram is used to gain access to this function. This procedure opens new possibilities of noncoherent-object information processing. Examples of matched filtering, low-pass filtering, and high-pass filtering are discussed. The underlying theory has its roots in the fundamental Van Cittert–Zernike theorem of the theory of partial coherence.

Pattern recognition using reduced information content filters.

Abstract: Pattern recognition by optical spatial filtering procedures is discussed using general considerations with the objective of reducing the information content in the spatial filter. The achievement of this objective is very useful toward the wide application of spatial light modulators and also for facilitating distortion invariant recognition. The proposed novel approach is demonstrated by an example employing bipolar spatial filters for rotation invariant pattern recognition.

Fourier Spectrum Techniques For Characterization Of Spatial Noise In Imaging Arrays

Abstract: Noise performance in imaging arrays is often specified simply by the variance of the pixel levels. In this paper a more complete characterization technique is presented, based on the spatial-frequency power spectrum of the noise data on the detectors. This is seen to provide additional information for cases in which the noise spectrum is nonwhite. Experimental data demonstrate the nonwhite nature of the spectrum under certain conditions, especially resulting from spatial correlation of detector nonuniformity and from sampling-lattice-related artifacts in the data.

Signal-dependent phase distortion in optical correlators.

Abstract: We examine the effect of phase distortion inherent in a spatial light modulator on the performance of an optical correlator. We examine such areas as input plane distortion, input and Fourier plane distortion, effect of phase mismatch between these planes, and the effect of additive white noise. When large distortions are present and the proper compensation is incorporated into the filter, we find a significant enhancement in performance in that the correlation response converges to a δ function and the SNR increases significantly. A theory is presented to explain this behavior.

Experimental use of iteratively designed rotation invariant correlation filters

Abstract: Iteratively designed filters are incorporated into an optical correlator for position, rotation, and intensity invariant recognition of target images. The filters exhibit excellent discrimination because they are designed to contain full information about the target image. Numerical simulations and experiments demonstrate detection of targets that are corrupted with random noise (SNR ≈ 0.5) and also partially obscured by other objects. The complex valued filters are encoded in a computer generated hologram and fabricated directly using an electron-beam system. Experimental results using a liquid crystal spatial light modulator for real-time input show excellent agreement with analytical and numerical Computations.

Optical laser beam control device for printer

Abstract: A laser beam control device related to the present invention includes an optical filter in the path of propagation of the laser beam from a laser light source to an image forming surface to form an image with the laser beam transmitted through the filter, and controls the transmittance of the filter based on the result obtained by detecting the intensity of the transmitted laser beam and comparing the detected value with a value of image density set by an operator.

Optically active biological particle distinguishing apparatus

Abstract: The disclosure is directed to organic particle sorting and identification. High frequency pulses of circularly polarized light, alternating between left and right, is formed by passing the beam (12) from a laser (10) through, in succession, a beam expander (14), a polarizer (16), an optical modulator (18) driven by an oscillator (20) and focussing and shaping optics (22) to intersect a fast moving stream of organic particles (24). Circular intensity differential scattering and linear intensity differential scattering are monitored by collecting light scattered from stream (24) with, in succession, collection optics (28), optical modulator (30) driven by oscillator (31), polarizer (32), spatial filter (34), and photodetector (36).

Refractive turbulence profiling using synthetic aperture spatial filtering of scintillation.

Abstract: High spatial resolution vertical profiles of refractive turbulence Cn2 can be obtained using a translating airborne light source. From spatially filtered observations of the optical scintillation pattern on the ground, caused by atmospheric density fluctuations, it is possible to infer both vertical profiles of Cn2 and the shape of the refractive turbulence spectrum. Profiles of key parameters such as the turbulence microscale are thereby accessible from ground-based measurements. The required signal-to-noise ratio and resultant spatial and spectral resolutions are determined.

Two dimensional digital spatial filter for enhancement of point source

Abstract: A point source spatial filter determines the quality of a central point source or pixel under test to thereby detect point sources and minimize the signals from all sources other than the desired point source. The spatial filter incorporates a buffer apparatus for receiving pixel signals, memory apparatus for storing pixel data for the test pixel and surrounding pixels, comparator apparatus for comparing test pixel values against a given number of surrounding pixel values to determine if the test pixel is a local maximum or minimum value, subtraction apparatus for subtracting the value of the nearest-valued surrounding pixel from the test pixel value when the test pixel is determined to be a local maximum or minimum, and apparatus for indicating the difference between the value of the test pixel and that of the surrounding pixel of closest value. This difference value becomes the filter output, and serves to establish a value for the point source signal intensity which is then compared to a threshold to provide a detection flag.

A Fourier approach to diffraction of pulsed ultrasonic waves in lossless media

Abstract: A method based on a Fourier domain approach is presented for computing the diffraction of a pulsed ultrasound wave from a rigidly baffled source in lossless media. The propagation from a planar source is dependent on the total impulse response which is just the Green’s function. Computing the spatial transform of the point spread function gives the propagation transfer function which multiplies the spatial spectrum of the spatial excitation to produce the spatial spectrum of the propagated wave. The propagation transfer function can then be considered to be a time‐varying spatial filter. The results are valid for separable arbitrary time excitation and planar spatial distributions of the source. The solution is amenable to including the effects of a finite receiver. Results of different simulations using this method are included.

Pupil-function design for complex incoherent spatial filtering

Abstract: A procedure for designing pupil functions for four-channel, three-channel, and two-channel syntheses of complex incoherent point-spread functions is presented. This procedure is then generalized for synthesis of multiple bipolar point-spread functions. Examples of pupil-function design for complex syntheses are also presented.

Optical target recognition system

Abstract: Prior art optical image correlators are extremely cumbersome and do not use spatial light modulators. To determine whether an of-interest target is within a scene, the present invention optical correlator uses a laser diode, a spatial light modulator, a holographic lens array, a matched filter array and an inverse transform lens. In particular, the laser diode generates a coherent laser beam, which is expanded and collimated. Information of the of-interest target is encoded thereon by the spatial light modulator. The encoded laser beam is then directed to the holographic lens array, which replicates from the single laser beam a plurality of similar beams. These beams are focused onto a matched filter array having multiple matched filters, the number of which corresponds to the number of incoming beams. If there is a close match between an incoming beam and a corresponding matched filter, a high intensity light is emitted from that particular matched filter toward the inverse transform lens, from when the high intensity beam is focused onto a correlation plane, where the existence of of-interest targets is ascertained.

Quasiphase-only matched filtering

Abstract: L'idee de cette technique est le nivellement de tous les maxima du spectre d'energie du signal a filtre

Simple scheme for variable high‐power laser beam attenuation

Abstract: A venetian style infrared attenuator placed prior to a pinhole spatial filter results in variable high‐power laser attenuation. This attenuation scheme has a wide dynamic range, results in high‐quality Gaussian beams, does not introduce beam walk‐off error, and is independent of polarization.