Showing papers on "Image resolution published in 1991"

A model of regional primary production for use with coarse resolution satellite data

Abstract: A model of crop primary production, which was originally developed to relate the amount of absorbed photosynthetically active radiation (APAR) to net production in field studies, is discussed in the context of coarse resolution regional remote sensing of primary production. The model depends on an approximately linear relationship between APAR and the normalized difference vegetation index. A more comprehensive form of the conventional model is shown to be necessary when different physiological types of plants or heterogeneous vegetation types occur within the study area. The predicted variable in the new model is total assimilation (net production plus respiration) rather than net production alone or harvest yield.

Electronic still camera providing multi-format storage of full and reduced resolution images

Abstract: Electronic still imaging apparatus includes a digital signal processor (22) that transforms blocks of digital image signals derived from an image sensor (12) into sets of coefficient signals and encodes the coefficient signals into a stream of compressed signals. In addition, the digital processor generates reduced resolution image signals from the digital image signals and downloads both the compressed (high resolution) image signals and the reduced resolution image signals to a removable digital memory (24). By associating each high resolution image with its low resolution counterpart in a common multi-format image file, the image can be quickly accessed and a low resolution review image can be put up on a display device (116) without waiting for expansion and processing of the larger full resolution image.

Physical performance characteristics of spiral CT scanning.

Abstract: CT scanning in spiral geometry is achieved by continuously transporting the patient through the gantry in synchrony with continuous data acquisition over a multitude of 360-deg scans. Data for reconstruction of images in planar geometry are estimated from the spiral data by interpolation. The influence of spiral scanning on image quality is investigated. Most of the standard physical performance parameters, e.g., spatial resolution, image uniformity, and contrast, are not affected; results differ for pixel noise and slice sensitivity profiles. For linear interpolation, pixel noise is expected to be reduced by a factor of 0.82; reduction factors of 0.81 to 0.83 were measured. Slice sensitivity profiles are changed as a function of table feed d, measured in millimeters per 360-deg scan; they are smoothed as the original profile is convolved with the object motion function. The motion function is derived for linear interpolation that constitutes a triangle with a base line width of 2d and a maximal height equal to 1/d. Calculations of both the full width at half-maximum and the shape of the profiles were in good agreement with experimental results. The effect of the widened profiles, in particular of their extended tail ends, on image quality is demonstrated in phantom measurements.

Multisensor image fusion techniques in remote sensing

Abstract: Current and future remote sensing programs such as Landsat, SPOT, MOS, ERS, JERS, and the space platform's Earth Observing System (Eos) are based on a variety of imaging sensors that will provide timely and repetitive multisensor earth observation data on a global scale. Visible, infrared and microwave images of high spatial and spectral resolution will eventually be available for all parts of the earth. It is essential that efficient processing techniques be developed to cope with the large multisensor data volumes. This paper discusses data fusion techniques that have proved successful for synergistic merging of SPOT HRV, Landsat TM and SIR-B images. It is demonstrated that these techniques can be used to improve rectification accuracies, to depicit greater cartographic detail, and to enhance spatial resolution in multisensor image data sets.

Rainfall Parameter Estimation from Dual-Radar Measurements Combining Reflectivity Profile and Path-integrated Attenuation

Abstract: Rain rate estimation properties of multiparameter radar measurements combining radar reflectivity and microwave attenuations are studied through simulations using a two-year disdrometer dataset. In the first simulation, properties of “complete” multiparameter measurements, where error-free measurements are assumed for each radar resolution cell, are investigated. The result indicates that dual-parameter (DP) measurements provide an excellent accuracy in rain rate estimation. Most of the DP measurements possible from space are “semi-” dual-parameter (SDP) measurements, defined as DP measurements in which spatial resolution for the attenuation measurement is coarser than the resolution required for rain profiling. Considering this fact, an SDP measurement simulation is also made. The SDP measurement is an extension of the concept of the DP measurement in terms of the spatial resolution, and can provide information on raindrop size distribution (DSD) by employing a “two-scale” DSD model. It is shown...

Two-dimensional imaging through diffusing media using 150-fs gated electronic holography techniques

Abstract: We combine 150-fs holographic gating with specifically adapted electronic holography techniques to produce transmission images of objects embedded in diffusing material. The technique captures, without the use of scanning procedures, complete two-dimensional images with 150-fs temporal resolution, thereby yielding submillimeter spatial resolution through diffusing objects several centimeters thick.

Two-Dimensional Coherent Detection Imaging in Multiple Scattering Media Based on the Directional Resolution Capability of the Optical Heterodyne Method

Abstract: This paper describes a new application of optical heterodyne detection using a laser beam for two-dimensional imaging of the internal structure of strongly scattering media in which the structure is completely obstructed from normal visual observation. The directional resolution capability for image formation due to the excellent antenna properties of the heterodyne technique is verified experimentally using a ground glass to cause strong scattering of the signal beam. Successful image detection of a test target placed in a highly scattering absorptive medium, with spatial resolution better than 400 μm in the case of our experiments, demonstrates that this Coherent Detection Imaging (CDI) method can overcome the diffuse nature of images in media such as those of biomedical interest and others to achieve scanning and tomographic imaging.

Performance standards in positron emission tomography.

Abstract: A standard set of performance measurements is proposed for use with positron emission tomographs. This set of measurements has been developed jointly by the Computer and Instrumentation Council of the Society of Nuclear Medicine and the National Electrical Manufacturers Association. The measurements include tests of spatial resolution, scatter fraction, sensitivity, count rate losses and randoms, uniformity, scatter correction, attenuation correction, and count rate linearity correction.

Time-gated imaging through scattering media using stimulated Raman amplification.

Abstract: We propose the use of stimulated Raman scattering for time-gated image amplification and demonstrate its use for the detection of images through a strongly scattering material. Using 30-ps pulses from a frequency-doubled Nd:YAG laser, we have amplified and detected images through a suspension of nondairy creamer with a spatial resolution of less than 300 μm and at concentrations such that the nonscattered extinction ratio was e−33. Our time-gated image amplifier can produce images under conditions in which the scattering medium is sufficiently dense that an image cannot be seen by using multiple exposures on a streak camera or time-integrated exposures on a sensitive, low-noise CCD camera.

Image database incorporating low resolution index image data

Abstract: A mechanism for controlling the manner in which digitized image data files are stored on a digital data storage medium, such as a compact disc, in an opto-electronic image digitizing system in which a plurality of images that have been captured on an image storage medium, such as 35 mm film, are converted into a digital image representation and stored as respective high resolution image-representative data files. For each high resolution image-representative data file, an associated low resolution digitized image is stored within a low resolution index image data file. Selected ones or all of the low resolution image-representative data files within the index file may be read out and displayed as corresponding low resolution portions of a montage image to facilitate rapid viewing of the images.

The influence of specimen refractive index, detector signal integration, and non-uniform scan speed on the imaging properties in confocal microscopy

Abstract: SUMMARY Refraction of light in a specimen volume may cause aberrations that influence the imaging properties in confocal microscopy In this paper the influence on three-dimensional resolution and geometry is experimentally investigated for a uniform specimen volume It is found that the depth resolution is more severely affected than the lateral resolution This is unfortunate, because even under ideal conditions the depth resolution is lower than the lateral resolution Lateral image geometry is little affected by the specimen refractive index, whereas the depth scale can be considerably elongated or compressed The influence of a finite detector integration time is also considered This can give a noticeable, but not particularly severe effect on the image resolution in the line-scan direction Because the integration time can be accurately controlled, a shorter integration time can be used when maximum resolution is essential, albeit at the price of a higher noise level In scanning fluorescence microscopy a non-uniform scan speed may give large variations in bleaching over the specimen surface Experiments illustrate how serious such non-uniform bleaching effects can be when a specimen area is repeatedly scanned, for example when recording optical serial sections

Computing optical flow across multiple scales: an adaptive coarse-to-fine strategy

Abstract: Single-scale approaches to the determination of the optical flow field from the time-varying brightness pattern assume that spatio-temporal discretization is adequate for representing the patterns and motions in a scene. However, the choice of an appropriate spatial resolution is subject to conflicting, scene-dependent, constraints. In intensity-base methods for recovering optical flow, derivative estimation is more accurate for long wavelengths and slow velocities (with respect to the spatial and temporal discretization steps). On the contrary, short wavelengths and fast motions are required in order to reduce the errors caused by noise in the image acquisition and quantization process. Estimating motion across different spatial scales should ameliorate this problem. However, homogeneous multiscale approaches, such as the standard multigrid algorithm, do not improve this situation, because an optimal velocity estimate at a given spatial scale is likely to be corrupted at a finer scale. We propose an adaptive multiscale method, where the discretization scale is chosen locally according to an estimate of the relative error in the velocity estimation, based on image properties. Results for synthetic and video-acquired images show that our coarse-to-fine method, fully parallel at each scale, provides substantially better estimates of optical flow than do conventional algorithms, while adding little computational cost.

A linear array, scintillation crystal-photodiode detector for megavoltage imaging

Abstract: An imaging device has been developed to acquire images during external photon-beam radiotherapy treatments. It consists of a linear array of 128 zinc tungstate (ZnWO4) scintillation crystals each of which is individually optically coupled to a photodiode and associated electronics. The image is formed by scanning the linear array across the radiation field using a stepping motor under the control of a microcomputer. Image archive, display, and analysis are performed using a microVAX II computer. Results from a general theoretical analysis are presented before a detailed description of the particular detector construction. The mechanical design of the detector is such that the detector is automatically positioned to within a millimeter relative to the treatment source. This simplifies procedures for analyzing setup variations when comparing a treatment image to any other treatment, or planning, images. Image acquisition takes under 4 s with a contrast resolution of better than 1% at a spatial resolution of 2.5 mm in the object plane. The primary dose used to form these images is 0.55 cGy although the dose received by the patient will be closer to 25 cGy due to the linear scanning geometry and 3.8-s scan time that is used.

Algorithmic characterization of vehicle trajectories from image sequences by motion verbs

Abstract: Images of vehicles which move in traffic scenes recorded by a stationary camera have been detected and tracked without operator intervention. The resulting vehicle trajectories were projected from the image plane onto the street plane. A suitable system internal representation of about 90 German motion verbs was then exploited in order to automatically characterize trajectory segments in terms of natural language concepts. A multiresolution approach for feature matching has been developed which is robust enough to track vehicle images across hundreds of frames, despite considerable variations in size and projected velocity. Results from experiments with image sequences from real-world traffic scenes are presented. >

Atomic resolution in lensless low-energy electron holography.

Abstract: With the low-energy-electron projection microscope it has been possible to image the lattice of thin gold films with atomic resolution. A theory modeling the coherent point source as the origin of a spherical wave is capable of describing both the Gabor-type holograms as well as the automatically resolved lattice images of the gold films.

Energy extension in three-dimensional atomic imaging by electron emission holography.

Abstract: A method is introduced joining together forward-scattering diffraction data taken in a small angular window at different photoelectron energies. This method extends the usable range in phase space for three-dimensional image reconstruction. Examples based on theoretical simulations demonstrate that a spatial resolution of \ensuremath{\le}1 \AA{} is achievable. We also show that using a small angular window in the backscattering geometry eliminates splittings in the reconstructed image.

Method and apparatus for a multi-channel multi-frequency data acquisition system for nondestructive eddy current inspection testing

Abstract: The invention discloses an inspection system for detecting near surface flaws or defects in conductors using nondestructive eddy current testing suitable for industrial application. The system provides a method and apparatus for acquiring real time, synchronized, discrete eddy current measurement signals from a plurality of sufficiently disposed, spatially correlated eddy current probes then processing and formatting said measurement signals automatically over parallel data channels to accommodate digital processing techniques in order to produce on eddy current image. Utilizing digital image processing provides a capability for improving flaw detection limits while simultaneously enhancing image resolution.

Three-dimensional measuring apparatus

Abstract: In a three-dimensional measuring apparatus, a multi-slit projector comprises an actuator (46) for displacing at least one of first and second diffraction gratings (42,43) by only a minute distance in a direction perpendicular to the slit lights, and an image recognizing apparatus comprises an image arithmetic unit (105) for changing, each time a coded multi-slit light pattern is changed, weights assigned to the binarized image signals, and for summing up the last weighted binarized image signals or the image signals of the last added results read out from an image memory (44), with newly weighted binarized image signals, whereby the image resolution is improved, the memory capacity is reduced and the processing speed is increased.

Spatial filtering for depth of focus and resolution enhancement in optical lithography

Abstract: Spatial filtering at the lens pupil can achieve amplitude superposition for multiple images along the light axis and phase control between them. This enhances depth of focus while maintaining high resolution capability in optical lithography. Compared to conventional methods, three times larger depth of focus is expected for hole patterns with 20% improved resolution limit. For general pattern features, a 1.5–1.7 times larger depth of focus is expected at Rayleigh’s resolution limit.

Video camera having a vibrating image-processing operation

Abstract: A video camera includes a vibration generation section including a camera body having a lens system with an auto-focus mechanism, an image pickup element, arranged along an optical axis of the camera body, for picking up an optical image obtained through the lens system, and a piezoelectric actuator for linearly vibrating the image pickup element with a predetermined amplitude at a predetermined period along the direction of the optical axis, an image signal processing circuit for A/D-converting a plurality of images time-serially obtained at arbitrary positions within the amplitude of the image pickup element vibrating along the optical axis, and an image memory for storing the plurality of time-serial images, further including an image input processing section consisting of an in-focus decision/extraction circuit for selecting and extracting clear in-focus areas of a predetermined image area, and an image synthesizing circuit for selecting desired ones of the plurality of areas from the image memory and synthesizing the selected areas into one image. The video camera of this invention further includes an intrusion decision function wherein a time-serial image having small positional and time differences is used within picked image coordinates, an optical flow between these features areas is obtained, and intrusion is decided by using the FOE point from which motion vectors of a stationary object are generated from a motion vector string obtained from the corresponding area in this optical flow.

Evaluation of Measurements of Particle Size and Sample Area from Optical Array Probes

Abstract: The technique of using shadow images of particles, obtained in coherent illumination to measure particle size, is analyzed. The theory of Fresnel diffraction for an opaque disc was used to analyze shadow images of transparent spherical particles. A comparison of theoretical calculations with laboratory results supports the application of this approach to optical array probes. It is shown that the shadow image size of spherical particles is essentially dependent on the distance from the object plane. In particular, for drops with diameters of less than 100 µm, the errors in size measurement from the PMS OAP-200X may reach 65%. These results agree well with laboratory calibrations that use monodisperse water droplets. On the basis of calculated particle diffraction images, the shape of the sample area and its dependence on drop size were calculated. It was found that the sample area has a complicated sawtooth shape. Gaps oriented perpendicular to the axis of a laser beam occur in the sample area in...

An evaluation of the utility of NOAA AVHRR images for monitoring forest fire risk in Spain

Abstract: The principal objective of this study is the evaluation of the potentiality of the low spatial resolution and high temporal resolution images,such as the images scanned by the AVHRR sensor of the NOAA-9 satellite. These imagesare used for detection of forest fire in areas prone to be affected and for determining physiological conditions of vegetationcover during the year, in order that we can as certain the conditions under which such cover is most susceptible to fire.

Real-time imaging spectrometer

Abstract: An improved AOTF-based imaging spectrometer that has ability to electronically set the bandpass wavelength of an AOTF to any desired value in its wide tuning range, provides significant observational flexibility. This allows observations to be tailored in real-time and enables the spectrometer to address a wide range of objectives and permits real-time modification of the observational parameters, such as in flight or in other situations in which only remote control is possible. Various improvements in optical architecture provide simplified magnification variability, improved image resolution and light throughput efficiency and reduced sensitivity to ambient light. A preferred embodiment employs a camera zoom lens as the input lens. A TeO2 AOTF and a relay lens are placed at selected distances behind the back focal plane of the input lens, respectively. A charge coupled device (CCD) camera, which comprises a camera, camera zoom lens and a CCD detector is placed at a selected distance behind the relay lens. An RF signal generator is used to drive the AOTF. Two embodiments of the invention are disclosed herein. One operates in the visible/near-infrared domain, in the wavelength range of 0.48 to 0.76 microns. The other operates in the infrared wavelength range of 1.2 to 2.5 microns.

Precision position measurement of moving atoms using optical fields.

Abstract: We demonstrate optical techniques for precisely measuring the position of moving atoms. Micron spatial resolution is attained by the methods which ultimately will scale to yield nanometer resolution limited by the uncertainty principle.

Improved multilook techniques applied to SAR and SCANSAR imagery

Abstract: The multilook processing used in SAR (synthetic aperture radar) image formation to reduce the speckle noise is considered. Two multilook techniques are proposed for improving the radiometric resolution without altering the geometric resolution and the characteristics of the impulse response. These techniques are based on the formation of looks with different bandwidths. The final image is formed by giving each look a proper size and weighting, and by adding them incoherently. The looks with wide bandwidth contribute to an improvement of the overall geometric resolution, while the looks with narrow bandwidth improve the overall radiometric resolution. The equivalent number of looks is more than 2.3 times the number of independent looks and is superior to conventional multilook processing with overlapping. Finally, using the proposed techniques, an algorithm for efficient SAR and ScanSAR processing is presented, and its validity is proved by image comparison and analysis. >

Ultimate limits in ultrasonic imaging resolution.

Abstract: According to elementary theory, the resolution of an ultrasonic imaging system increases with the ultrasonic frequency. However, frequency is limited by frequency-dependent attenuation. For imaging at any required depth, resolution improvement beyond the limit imposed by ultrasonic frequency can be obtained by increasing the ultrasonic intensity. This is itself, however, dependent on safety considerations and the effects of nonlinearity. In homogeneous media, image resolution increases with decreasing f-number. Particularly at low f-numbers, however, tissue inhomogeneity leads to a deterioration in image quality. Inhomogeneity may also be considered in terms of phase aberration. It has been found that for a given aperture, image degradation due to phase aberration is worse at higher frequencies. Schemes have been proposed for correction of this problem, but so far model systems do not lend themselves to clinical application. Deconvolution is unsatisfactory, speed correction is impracticable and synthetic aperture scanning and holography are virtually useless in biological tissues. Ultrasound-computed tomography has had only limited success. Speckle reduction can improve target detectability, but at the expense of resolution. Time-frequency control provides a useful partial solution to the problem of resolution reduction resulting from attenuation. It is clear that improved resolution would result in significant clinical benefits. An optimisation system for aperture size and ultrasonic frequency is proposed with signal averaging for resolution enhancement of a defined object area. This would have a compact ultrasonic beam and would allow frame rate to be traded for resolution, by means of signal averaging.

Contrast, resolution, and detectability in MR imaging.

Abstract: With the introduction of fast scan techniques and high field imagers, the ability to achieve very high resolution MR images in reasonable imaging times is now possible. Increased resolution allows for better detection of small, high contrast pathological features, but at some cost. Increasing resolution leads to a nonrecoverable decrease in signal-to-noise ratio per pixel and a loss of low contrast detectability for constant imaging time. This article examines the tradeoffs between image resolution, signal-to-noise ratio, and low contrast detectability in MR imaging. Contrast detail curves are presented for images collected in a constant imaging time, with constant field of view and bandwidth but at different resolutions, and these are compared with theoretical curves. The problem of measuring contrast levels in magnitude images, with different resolutions and receiver attenuation values, is discussed and a definition that accommodates these parameters developed. In addition, a clinical example is shown demonstrating a decrease in soft tissue differentiation with increasing resolution, again for fixed imaging time. The results indicate that moving to high resolution imaging matrices requires consideration be given to the sacrifice in low contrast detectability that occurs. Most importantly, it is shown that filtering a high resolution image to a lower resolution image, through nearest neighbor averaging, does not regain the detectability lost in initially collecting the high resolution image.

X-ray optics. 2: A technique for high resolution spectroscopy

Abstract: A novel combination of optical elements and properties is combined to achieve high spectral resolution using grazing incidence optics of modest quality. We show through analysis and ray tracing of examples that using radial groove gratings at high blaze angles in the manner of an echelle spectrograph can provide high spectral resolution. We compare this arrangement to the conventional in-plane designs and show the off-plane to be superior in nearly every respect. Cross dispersion can be provided by the energy resolution of a CCD detector. Then, we show how additional resolution can be squeezed from the system by strategic placement of gratings to take advantage of the azimuthal response of a Wolter x-ray optic. With a telescope that has only 30-sec of arc imaging we are able to support resolution lambda/deltalambda of 3000, while a conventional design at the same graze angle supports resolution of only 200.

Apparatus and method for non-destructive testing using multi-frequency eddy currents

Abstract: A method for improving eddy current flaw detection by simultaneously exciting a select plurality of eddy current probe elements with a multiplicity of select frequencies in a simultaneous parallel or serial manner to form a corresponding multiplicity of direct and/or differential images which can be processed together for improved eddy current image resolution Select eddy current probe elements when driven at select multiple frequencies further provide a capability for simultaneous flaw detection and characterization by dual resolution scanning Dual flaw resolution is accomplished by first locating a flaw using low resolution frequencies; and thereupon, switching to higher resolution frequencies to characterize the flaw