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Showing papers on "Point spread function published in 1973"


Journal ArticleDOI
TL;DR: In this article, the Fourier transform of a blurred image is used to identify the optical transfer function, provided that it is one of the suitable common simple forms, or to determine certain parameters of the transfer function if its form is known.
Abstract: In cases in which there are zeros in the optical transfer function, display of the absolute value of the Fourier transform of a blurred image may allow these zeros to be seen, if the noise level is low enough. This can be used to identify the optical transfer function, provided that it is one of the suitable common simple forms, or to determine certain parameters of the optical transfer function if its form is known. Examples of the use of this technique in the generation of restoring filters for image enhancement are presented.

109 citations


Journal ArticleDOI
TL;DR: Analysis of detection-probability data combined with signal-to-noise analysis of contrast-sensitivity data yield the fundamental visual-system parameters required to predict image-detection performance.
Abstract: An image-detector model of the visual system is described. Analysis of detection-probability data combined with signal-to-noise analysis of contrast-sensitivity data yield the fundamental visual-system parameters required to predict image-detection performance. The results for background luminances ranging from 10−3 to 102 millilamberts include the values of the threshold detection criterion or signal-to-noise ratio, the response time, the effective responsive quantum efficiency, the effective angular width of the point spread function, and the effective angular width of the maximum photoreceptor field belonging to the minimum-bandwidth spatial filter. Excellent agreement between theoretical curves and experimental data is shown.

40 citations


Journal ArticleDOI
TL;DR: Photosensor aperture shaping and line-scan spacing are investigated as a means for reducing the impact of aliasing on the spatial detail of the reconstructed image.
Abstract: Optical-mechanical scanning techniques are generally employed in instruments specifically designed to characterize variations in scene brightness spectrally or radiometrically. The effect of aliasing, which can be caused by line-scan sampling, on the spatial detail of the reconstructed image has therefore been of little concern. Emphasis of some recent applications of optical-mechanical scanning techniques is, however, on the spatial characterization of the scene. As is shown here, such images can be severely degraded by aliasing. Photosensor aperture shaping and line-scan spacing are investigated as a means for reducing this degradation.

35 citations


Journal ArticleDOI
TL;DR: It is shown that a large class of space-variant operations may be decomposed into the cascade of invertible coordinate transformations and space-invariant systems; a block-diagram representation of this technique is presented.
Abstract: A complete analysis of motion degradation in two-dimensional linear incoherent optical systems is presented from a system viewpoint. An equivalent space-variant point-spread function is derived from knowledge of the system motion, and the special characteristics of space-invariant and one-dimensional systems are considered. The analysis includes the effects of two different models for geometrical distortion in motion-degraded imaging and derives the distortions for aerial imaging. It is shown that a large class of space-variant operations may be decomposed into the cascade of invertible coordinate transformations and space-invariant systems; a block-diagram representation of this technique is presented. A number of examples of common types of motion blur are included, as well as computer simulations of space-variant blur and the decomposition process.

31 citations


Journal ArticleDOI
TL;DR: In certain applications, especially x-ray and gamma-ray photography, pinhole cameras provide one of the only methods of producing sharp images, providing theautocorrelation function of the array is sharply peaked.
Abstract: In certain applications, especially x-ray and gamma-ray photography, pinhole cameras provide one of the only methods of producing sharp images. To increase the image quality, the use of an array of multiple pinholes is found valuable. The resulting blurred image must then be decoded. A particularly direct method of decoding using the original array of pinholes is possible, providing theautocorrelation function of the array is sharply peaked. Preliminary results with representative arrays are discussed.

27 citations


Journal ArticleDOI
TL;DR: The Mertz and Gray analysis of image scanning in terms of multidimensional Fourier transforms is reformulated using a different coordinate system, leading to scanning equations that emphasize the importance of the scanning apertures.
Abstract: The Mertz and Gray analysis of image scanning in terms of multidimensional Fourier transforms is reformulated using a different coordinate system. A simplified mathematical notation is used for this analysis leading to scanning equations that emphasize the importance of the scanning apertures. Other image processes involving scanning are described in terms of their multidimensional Fourier transforms. These include a novel two-dimensional screening technique, and its comparison with a simple screening method and with conventional photographic screening processes. The effect on video spectra of aperture filtering and an analysis of television line interlacing are also given. The conditions for the validity of the unidimensional analysis of some of these image processing systems are indicated.

24 citations


Journal ArticleDOI
TL;DR: In this paper, a mask is placed in the plane, conjugate to the plane containing the plurality of object-illuminating sources, and an aperture in this mask is then moved to take positions to transmit only the light from one of the illuminating points at a time and to block the other points.
Abstract: This method consists of two steps. The first is to illuminate the object with a plurality of point sources each of which is mutually coherent with the reference source. All the points are contained within the pupil of the optical apparatus. The second step takes place after the hologram has been made in the manner mentioned. During the reconstruction, a mask is placed in the plane, conjugate to the plane containing the plurality of object-illuminating sources. An aperture in this mask is then moved to take positions to transmit only the light from one of the plurality of points at a time and to block the light from all the other points. The images thus detected are additive in intensity, simulating the plurality of illuminating point sources to be mutually incoherent.

21 citations


Journal ArticleDOI
TL;DR: In this paper, a method for increasing the linear dynamic range of coherent-optical spatial filters, with special reference to holographic image-deblurring filters, is presented. But the results show that a good transfer function can be achieved with a hologram-only filter.
Abstract: We report on a new method for increasing the linear dynamic range of coherent-optical spatial filters, with special reference to holographic image-deblurring filters. In the filter-generating step, a transmission grating is placed in contact with the transparency representing the spread function of the blur. The spectrum of the spread function then appears in a series of equally spaced islands of different intensities, each occupying a different region of the nonlinear characteristic of the recording medium. Each spatial frequency can then be properly exposed somewhere on the filter, even with a film of limited dynamic range. In the image -processing step, the grating is superposed on the blurred image, the spectrum of which then falls on all the islands of the filter. In this way, the filtering operation is done in parallel channels, each with a different nonlinear characteristic. The channels are combined in the output plane by superposing a grating on the filtered aerial image and viewing this plane through an optical system that does not resolve the grating. Theory, computer simulations, and experimental results are presented. The results show in particular that a good transfer function can be achieved with a hologram-only filter.

19 citations


Journal ArticleDOI
TL;DR: This method accomodates the problem of noncircularly symmetric imaging system point-spread functions, provides for controlled extent of the preprocessing filter to minimize distortion due to transients resulting from truncation errors and edge effects, and can be used with various kinds of system noise.
Abstract: A linear shift-invariant preprocessing technique is described which requires no specific knowledge of the image parameters and which is sufficiently general to allow the effective radius of the composite imaging system to be minimized while constraining other system parameters to remain within specified limits.

15 citations


Journal ArticleDOI
J. Gasper1
TL;DR: In this paper, the point spread function of a transparent luminescing screen-receiver system was derived from the optical paths and attenuations of the luminescent energy producing the spread function.
Abstract: Transparent luminescing screens can be used as image transducers in radiographic and image-intensifier systems. The modulation transfer function (MTF) and efficiency of these screens when used in conjunction with a receiver or recording medium are obtained from the derivation of the point spread function of the screen–receiver system. The derivation accounts for all optical paths and attenuations of the luminescent energy producing the spread function. Both the theoretical MTF’s and energy-transducing efficiencies of several screen–receiver systems are presented for various system parameters. The MTF of an actual (ZnS) screen–film system, computed from this derivation, was found to be in excellent agreement with the MTF of the system determined by photographic photometry.

10 citations


Journal ArticleDOI
G. Groh1, E. Klotz1, Hermann Weiss1
TL;DR: A demonstration of the method is given by showing the dependence of the MTF on shape and size of the focal spot of the x-ray tube and the nonshift invariance of a system using a rotating anode tube.
Abstract: A method for the evaluation of the two-dimensional MTF of x-ray systems is described. In a first step a statistical distribution of lead grains is imaged by the x-ray systems. In the second step this image is Fourier transformed in a coherent optical processor giving the two-dimensional display of the MTF. A demonstration of the method is given by showing the dependence of the MTF on shape and size of the focal spot of the x-ray tube and the nonshift invariance of a system using a rotating anode tube. Furthermore the application of the method in tomographic x-ray systems is tested.

Journal ArticleDOI
TL;DR: The unusual transfer function characteristics of the SAS are shown to obtain larger sampling distances than those required by the Whittaker-Shannon sampling theory.
Abstract: This paper discusses the application of a synthetic aperture system (SAS) for the formation of infrared, images The SAS of primary interest is a hexagoiial array of six circular apertures; special emphasis is placed on a one-dimensional model that describes the salient features of the two-dimensional model In infrared images, in the 8–14-μm region, conventional detectors are too large to sample the image without aliasing the spatial spectrum The unusual transfer function characteristics of the SAS are shown to obtain larger sampling distances than those required by the Whittaker-Shannon sampling theory One possible detector array that will correctly sample the image is presented