Showing papers on "Image resolution published in 1987"
TL;DR: The history and scope of remote sensing is described in detail in this paper, where the authors present a detailed overview of the field of Remote Sensing and its application in agriculture, land use and land cover.
Abstract: Preface. Part I: Foundations. History and Scope of Remote Sensing. Electromagentic Radiation. Part II: Image Acquisition. Photographic Sensors. Digital Data. Image Interpretation. Land Observation Satellites. Active Microwave and Lidar. Thermal Radiation. Image Resolution. Part III: Analysis. Preprocessing. Image Classification. Field Data. Accuracy Assessment. Hyperspectral Remote Sensing. Part IV: Applications. Geographic Information Systems. Plant Sciences. Earth Sciences. Hydrospheric Sciences. Land Use and Land Cover. Global Remote Sensing.
3,445 citations
TL;DR: In this paper, the spatial structure of images as a function of spatial resolution is measured for selecting the appropriate scale for remote sensing, and graphs are obtained by imaging the scene at fine resolution and then collapsing the image to successively coarser resolutions while calculating the local variance.
1,277 citations
TL;DR: This work model the speckle according to the exact physical process of coherent image formation and accurately represents the higher order statistical properties of speckel that are important to the restoration procedure.
Abstract: Speckle is a granular noise that inherently exists in all types of coherent imaging systems. The presence of speckle in an image reduces the resolution of the image and the detectability of the target. Many speckle reduction algorithms assume speckle noise is multiplicative. We instead model the speckle according to the exact physical process of coherent image formation. Thus, the model includes signal-dependent effects and accurately represents the higher order statistical properties of speckle that are important to the restoration procedure. Various adaptive restoration filters for intensity speckle images are derived based on different model assumptions and a nonstationary image model. These filters respond adaptively to the signal-dependent speckle noise and the nonstationary statistics of the original image.
701 citations
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TL;DR: It is shown that ``edge focusing'', i.e., a coarse-to-fine tracking in a continuous manner, combines high positional accuracy with good noise-reduction, which is of vital interest in several applications.
Abstract: Edge detection in a gray-scale image at a fine resolution typically yields noise and unnecessary detail, whereas edge detection at a coarse resolution distorts edge contours. We show that ``edge focusing'', i.e., a coarse-to-fine tracking in a continuous manner, combines high positional accuracy with good noise-reduction. This is of vital interest in several applications. Junctions of different kinds are in this way restored with high precision, which is a basic requirement when performing (projective) geometric analysis of an image for the purpose of restoring the three-dimensional scene. Segmentation of a scene using geometric clues like parallelism, etc., is also facilitated by the algorithm, since unnecessary detail has been filtered away. There are indications that an extension of the focusing algorithm can classify edges, to some extent, into the categories diffuse and nondiffuse (for example diffuse illumination edges). The edge focusing algorithm contains two parameters, namely the coarseness of the resolution in the blurred image from where we start the focusing procedure, and a threshold on the gradient magnitude at this coarse level. The latter parameter seems less critical for the behavior of the algorithm and is not present in the focusing part, i.e., at finer resolutions. The step length of the scale parameter in the focusing scheme has been chosen so that edge elements do not move more than one pixel per focusing step.
498 citations
TL;DR: It is shown that the scene amplitude spectra follow an approximate reciprocal variation with frequency, and that the correlation function can be described by a one-step autoregressive model.
Abstract: Digitized records of terrain scenes were produced using a technique of photographic colorimetry. Each record consisted of three tristimulus images (X,Y, and Z) which were analyzed for their color statistics, spatial frequency content, and image correlation. Interactions between color and space were examined using a cone receptor transformation. It is shown that the scene amplitude spectra follow an approximate reciprocal variation with frequency, and that the correlation function can be described by a one-step autoregressive model. The results are discussed in terms of methods for optimum image coding in human and machine vision.
495 citations
TL;DR: In this paper, the authors formalize the classical diffraction stack by relating it to linearized seismic inversion and the generalized Radon transform, which can handle both complex velocity models and arbitrary configurations of sources and receivers.
Abstract: A new approach to seismic migration formalizes the classical diffraction (or common-tangent) stack by relating it to linearized seismic inversion and the generalized Radon transform. This approach recasts migration as the problem of reconstructing the earth’s acoustic scattering potential from its integrals over isochron surfaces. The theory rests on a solution of the wave equation with the geometrical-optics Green function and an approximate inversion formula for the generalized Radon transform. The method can handle both complex velocity models and (nearly) arbitrary configurations of sources and receivers. In this general case, the method can be implemented as a weighted diffraction stack, with the weights determined by tracing rays from image points to the experiment’s sources and receivers. When tested on a finite-difference simulation of a deviated-well vertical seismic profile (a hybrid experiment which is difficult to treat with conventional wave-equation methods), the algorithm accurately reconstructed faulted-earth models. Analytical reconstruction formulas are derived from the general formula for zero-offset and fixed-offset surface experiments in which the background velocity is constant. The zero-offset inversion formula resembles standard Kirchhoff migration. Our analysis provides a direct connection between the experimental setup (source and receiver positions, source wavelet, background velocity) and the spatial resolution of the reconstruction. Synthetic examples illustrate that the lateral resolution in seismic images is described well by the theory and is improved greatly by combining surface data and borehole data. The best resolution is obtained from a zero-offset experiment that surrounds the region to be imaged.
430 citations
TL;DR: A low-cost and simple technique for encryption of two-dimensional patterns and shapes based on the superposition of random grids is suggested and demonstrated.
Abstract: A low-cost and simple technique for encryption of two-dimensional patterns and shapes is suggested and demonstrated. The method is based on the superposition of random grids.
320 citations
TL;DR: In this paper, the capability of the atomic force microscope to image the surface of an electrically insulating solid with atomic resolution was demonstrated, including graphite and molybdenum disulfide.
Abstract: We have demonstrated the capability of the atomic force microscope to image the surface of an electrically insulating solid with atomic resolution. Images of highly oriented pyrolytic boron nitride taken in air show atomic corrugations with a lateral resolution better than 3 A. Low‐noise images of graphite and molybdenum disulfide are also presented.
307 citations
251 citations
TL;DR: A code modeled on the simple cells of the primate striate cortex is explored, which maps a digital image into a set of subimages (layers) that are bandpass in spatial frequency and orientation and which is reconstructed from the code.
Abstract: Hypothetical schemes for neural representation of visual information can be expressed as explicit image codes. Here, a code modeled on the simple cells of the primate striate cortex is explored. The Cortex transform maps a digital image into a set of subimages (layers) that are bandpass in spatial frequency and orientation. The layers are sampled so as to minimize the number of samples and still avoid aliasing. Samples are quantized in a manner that exploits the bandpass contrast-masking properties of human vision. The entropy of the samples is computed to provide a lower bound on the code size. Finally, the image is reconstructed from the code. Psychophysical methods are derived for comparing the original and reconstructed images to evaluate the sufficiency of the code. When each resolution is coded at the threshold for detection artifacts, the image-code size is about 1 bit/pixel.
241 citations
TL;DR: A technique has been developed that significantly improves the image resolution and reduces motion artifacts in conventional two- and three-dimensional Fourier transform magnetic resonance imaging sequences and has allowed diagnostic quality T1- and T2-weighted images to be obtained with one acquisition per view, thus reducing the total scan time.
Abstract: A technique has been developed that significantly improves the image resolution and reduces motion artifacts in conventional two-dimensional Fourier transform and three-dimensional Fourier transform magnetic resonance imaging sequences. Modifications on the gradient waveforms completely refocus the transverse magnetization at the echo time, regardless of the motion occurring between the time of the 90 degrees radiofrequency excitation and the echo time (within-view). This accomplishes suppression of motion artifacts and regains the signal from flowing blood and CSF. Images of the head, abdomen, chest, and spine are reproduced which show the increase in signal and anatomical detail that would otherwise be degraded and lost in artifact noise. This technique has reduced the practical difficulty of obtaining clinically diagnostic T2-weighted abdominal images. It also has allowed diagnostic quality T1- and T2-weighted images to be obtained with one acquisition per view, thus reducing the total scan time.
TL;DR: An optimal technique for CT of the lung parenchyma should include thin-collimation, targeted scans reconstructed with a high-spatial-frequency algorithm and, in some patients, increased kilovolt peak or milliamperage.
Abstract: The influences of kilovolt peak, milliamperage, reconstruction algorithm, targeting, and image magnification on thin-section (1.5-mm) computed tomography (CT) of the lung were studied in phantoms and patients. Retrospective targeted reconstruction (25-cm field of view) improved spatial resolution, while magnification did not. The bone reconstruction algorithm improved spatial resolution, compared with the standard algorithm, and in patients, bone algorithm images were considered superior to standard reconstructions. Although using the bone algorithm increases the visible image noise, increasing the kilovolt peak and the milliamperage can reduce this noise. However, in the patients studied, this reduction in noise was not usually judged as significant, except in the posterior, paravertebral part of the lung. An optimal technique for CT of the lung parenchyma should include thin-collimation, targeted scans reconstructed with a high-spatial-frequency algorithm and, in some patients, increased kilovolt peak or milliamperage.
TL;DR: A high resolution image is found such that when simulating the imaging process the authors get low resolution images closest to the observed images, and simulated annealing is also used for the optimization process.
TL;DR: In this paper, the effect of spatial resolution on the degree of internal variability within land cover classes and then how this within-class variance affects classification accuracy was examined and the extent of this improvement was found to be as much as 25 per cent depending on the type of spatial filter used, the window size of the filter, the spatial resolution of the data and the land-cover type bei...
Abstract: A study is made to assess the effect of spatial resolution on the degree of internal variability within land-cover classes and then to examine how this within-class variance affects classification accuracy. Airborne Multispectral Scanner data flown at 5 m resolution are degraded to simulate 10 and 20 m data. Classification accuracies within internally homogeneous classes are found to be high at all spatial resolutions. In contrast, classification accuracies of land-cover types characterized by a high degree of internal variability or scene noise improve by up to 20 per cent as spatial resolution is coarsened because the proportion of scene noise is reduced. A further improvement in classification can be achieved by smoothing the imagery prior to classification using various spatial filters. The extent of this improvement was found to be as much as 25 per cent depending on the type of spatial filter used, the window size of the filter, the spatial resolution of the data and the land-cover type bei...
TL;DR: The detectability of microcalcifications in the digital mammograms is improved by unsharp-mask filtering; the processed mammograms still provide lower accuracy than the conventional mammograms, however, chiefly because of increased false-positive detection rates for the processed images at each subjective confidence level.
Abstract: We investigated the spatial resolution requirement and the effect of unsharp-mask filtering on the detectability of subtle microcalcifications in digital mammography. Digital images were obtained by digitizing conventional screen-film mammograms with a 0.1 X 0.1 mm2 pixel size, processed with unsharp masking, and then reconstituted on film with a Fuji image processing/simulation system (Fuji Photo Film Co., Tokyo, Japan). Twenty normal cases and 12 cases with subtle microcalcifications were included. Observer performance experiments were conducted to assess the detectability of subtle microcalcifications in the conventional, the unprocessed digital, and the unsharp-masked mammograms. The observer response data were evaluated using receiver operating characteristic (ROC) and LROC (ROC with localization) analyses. Our results indicate that digital mammograms obtained with 0.1 X 0.1 mm2 pixels provide lower detectability than the conventional screen-film mammograms. The detectability of microcalcifications in the digital mammograms is improved by unsharp-mask filtering; the processed mammograms still provide lower accuracy than the conventional mammograms, however, chiefly because of increased false-positive detection rates for the processed images at each subjective confidence level. Viewing unprocessed digital and unsharp-masked images in pairs resulted in approximately the same detectability as that obtained with the unsharp-masked images alone. However, this result may be influenced by the fact that the same limited viewing time was necessarily divided between the two images.
TL;DR: The imaging performance of a storage phosphor system for digital projection radiography is studied in which the x-ray image is temporarily stored in a light-stimulable phosphor plate which is subsequently read out by a scanning laser beam.
Abstract: The imaging performance of a storage phosphor system (SPS) for digital projection radiography is studied in which the x‐ray image is temporarily stored in a light‐stimulable phosphor plate which is subsequently read out by a scanning laser beam. The imaging performance of this system has been analyzed for two types of imaging plates. The spatial resolution is described by the modulation transfer function and the signal‐to‐noise (S/N) ratios of the recorded image data are measured in terms of noise‐equivalent quanta and detectivequantum efficiency. Their dependence on detector entrance dose and space and spatial frequency is discussed. A detailed analysis of the different sources of image noise is given to outline the intrinsic features and limits of the system. Finally, the S/N behavior of the SPS is compared with published data of screen–film systems.
TL;DR: A procedure is developed for combining high spatial resolution panchromatic data with lower resolution multispectral data in order to produce high spatialresolution digital data in multisectral form.
TL;DR: In this paper, the authors examined the information content of Landsat TM and MSS data to assess the ability of digitally differentiate urban and near-urban land covers around Miami, FL.
Patent•
14 Apr 1987TL;DR: In this paper, the pixel density of the input image data is converted, by a pixel converter, to a pixel density matching that of the printer, according to a conversion ratio set by the pixel-density conversion ratio settingter.
Abstract: Image data having a predetermined pixel density, and output from a personal computer, is supplied to an image-resolution conversion apparatus connected to a printer having a pixel density different from the above predetermined pixel density. In the image resolution conversion apparatus, the pixel density of the input image data is converted, by a pixel converter, to a pixel density matching that of the printer, according to a conversion ratio set by a pixel-density conversion ratio setter for setting a ratio of pixel-density conversion, from the pixel density of the personal computer to that of the printer. The pixel-density converted image data is then supplied to and printed by the printer.
TL;DR: In this paper, a method is described that measures displacements from synthetic aperture radar digital imagery with fine spatial resolution, and does so fully automatically, and many small areas of ice common to two images are identified by correlating the two images.
Abstract: Spatial differences in sea ice displacement affect ice stress, ice production, and the mass balance of the ice cover. Our concepts about the spatial structure of this field have been undernourished because of a paucity of data with high spatial detail and because of the tedium of extracting such measurements from images manually. A method is described that measures displacements from synthetic aperture radar digital imagery with fine spatial resolution, and does so fully automatically. Many small areas of ice common to two images are identified by correlating the two images. The strategy is to acquire a crude displacement field first from highly averaged images, and to refine this field with images of successively higher resolution. The median discrepancy between automatically and manually measured displacements is three pixels (0.075 km). The algorithm operates successfully on compact ice with large floes and modest rotation rates; we believe it will prove applicable to most of the arctic ice cover throughout the year.
TL;DR: In this article, the relationship between image centroid motion and large-telescope long-exposure image size was investigated for the cases of absolute motion measured with a single aperture and differential motion with two apertures.
Abstract: Relations between image centroid motion and large-telescope long-exposure image size are given for the cases of absolute motion measured with a single aperture and differential motion measured with two apertures. The effect of a finite exposure time in the measurement of image positions is included in the analysis, and is shown to be of crucial importance, especially in the measurement of differential image motion. For example, the contribution of the free atmospherre to the mean square differential motion can be underestimated by more than a factor of ten in realistic circumstances if an exposure time of 1/30 s is used.
TL;DR: It is demonstrated that unspeckled images of coherently illuminated, diffuse objects can be formed from measurements of backscattered laser-speckle intensity.
Abstract: We demonstrate that unspeckled images of coherently illuminated, diffuse objects can be formed from measurements of backscattered laser-speckle intensity. The theoretical basis for this imaging technique is outlined, and results of computer experiments that successfully construct images from digitally simulated laser-speckle measurements are presented.
TL;DR: The algorithm is basically an enhanced EM (expectation maximization) algorithm with improved frequency response and is promising to achieve significant saving in computation compared to the standard 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.
TL;DR: The finding that 2.5 lp/mm is the required spatial resolution makes construction of a total digital radiology department possible with present state-of-the-art technology.
Abstract: The minimum spatial resolution required for a total digital radiology department has yet to be defined. A pilot study designed to provide this information was performed. Abnormal and normal radiographic images of children were digitized and redisplayed on film at spatial resolutions of 5.0, 2.5, 1.25, and 0.625 lp/mm. These resolutions are comparable to a digital display of a 14 X 14 in. chest image having pixel elements of 4096 X 4096, 2048 X 2048, 1024 X 1024, and 512 X 512, respectively. Contrast resolution was maintained at 12 bits or 4096 gray levels. The three phases of data acquisition were (1) the standard analysis of receiver operating characteristics, (2) a checklist evaluation of the "seeability" of important structures, and (3) a comparison of all resolutions and a discernment of usability. Fifteen radiologists participated in the study. On the basis of the pediatric cases used, the results showed that the needed spatial resolution for a total digital radiology department may be around 2.5 lp/...
01 Jan 1987
TL;DR: The moderate resolution imaging spectrometer (MODIS) is discussed as an Earth-viewing sensor that is planned as a facility instrument for the Earth Observing System (Eos) scheduled to begin functioning in the mid-1990s as mentioned in this paper.
Abstract: The moderate resolution imaging spectrometer (MODIS) is discussed as an Earth-viewing sensor that is planned as a facility instrument for the Earth Observing System (Eos) scheduled to begin functioning in the mid-1990s. The MODIS is composed of two mutually supporting sensors that cover a swath width sufficient to provide nearly complete two-day global coverage from a polar-orbiting, sun-synchronous, serviceable platform. High signal-to-noise ratios are to be provided, e.g. 500 to 1 or greater with 10-12-bit quantization over the dynamic ranges of the spectral bands. MODIS' lifetime is expected to be about ten years. One of the MODIS sensors is termed MODIS-N, where N signifies nadir-viewing. The companion to MODIS-N is MODIS-T, where T signifies a tiltable field-of-view. The development of the MODIS facility from conceptual design studies (Phase-A) into detailed design studies (Phase-B) is discussed. >
15 Jan 1987-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this paper, the authors observed a significant increase in dark current and systematic distortions in the measured coordinates which are explained in terms of a decrease in the effective donor concentration, which can be explained by a reduction in the amount of ionizing particles per cm2.
Abstract: Silicon strip detectors with 5 μm spatial resolution have been used during 1982–1985 in the ACCMOR spectrometer at CERN. After a local beam flux of about 1014 minimum ionizing particles per cm2 we observe a significant increase in dark current and systematic distortions in the measured coordinates which are explained in terms of a decrease in the effective donor concentration.
Patent•
22 Apr 1987TL;DR: In this article, the entire image is divided into a plurality of regional images and filtering optimized for each pixel image is effected using a standard deviation computed for each regional image and a density difference between pixel images.
Abstract: In an unsharp masking processing for sharpening images such as radiographic images, an emphasizing coefficient of an image and parameters for real-time change of picture quality are set interactively. The entire image is divided into a plurality of regional images and filtering optimized for each pixel image is effected using a standard deviation computed for each regional image and a density difference between pixel images.
TL;DR: High resolution airborne or vehicular imaging systems are often limited in performance by mechanical vibrations, so data can be used to statistically define expected performance of high resolution systems and to aid accordingly in sensor selection.
Abstract: High resolution airborne or vehicular imaging systems are often limited in performance by mechanical vibrations. High vibration frequency MTF is known. Low vibration frequency MTF is a random process analyzed here. Average and ideal maximum spatial frequency limitations are calculated. Plots are presented to describe the number of independent images of the same object required so that at least one "lucky shot" with a given spatial frequency requirement is obtained with a given probability. Examples for short and long relative exposures are included. These data can be used to statistically define expected performance of high resolution systems and to aid accordingly in sensor selection. The probability of achieving higher resolution improves noticeably as relative exposure time is decreased.
TL;DR: It is demonstrated that an alternate low-pass filter can be used to improve contrast resolution with a loss in spatial resolution and yet not result in Gibbs artifact by properly specifying the number of samples averaged for each phase encoding index.
Abstract: Gibbs artifact in magnetic resonance imaging results when band-limited interpolation is used. This is typically done when there are more reconstructed pixels in the phase encoding direction of the image than corresponding phase encoding measurements. Such sampling is effectively an ideal (in a noise sense) low-pass filter which provides a maximal improvement in contrast resolution at the expense of a decrease in spatial resolution. In this paper we demonstrate that an alternate low-pass filter can be used to improve contrast resolution with a loss in spatial resolution and yet not result in Gibbs artifact. We show that the noise performance of this filter can be made to approach that of an ideal filter by properly specifying the number of samples averaged for each phase encoding index.