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Showing papers on "Point spread function published in 1981"


Journal ArticleDOI
TL;DR: In this article, a method for image reconstruction that processes the data in polar rather than rectangular coordinates and does not require backprojection is described, based on the decomposition of the object and its shadow (set of projections) into circular harmonics, or radial modulators of angular Fourier components.
Abstract: A method is described for image reconstruction that processes the data in polar rather than rectangular coordinates and does not require backprojection. It is based on the decomposition of the object and its shadow (set of projections) into circular harmonics, or radial modulators of angular Fourier components. Inverse filters are derived that enable the radial modulators of the object to be reconstructed from those of the shadow. An optical system for reconstruction using the method is proposed.

51 citations


Journal ArticleDOI
TL;DR: In this paper, the Fourier operator description of Fourier optics is extended and applied to holography, and a compact expression for the description of the holographically reconstructed field distribution at an arbitrary plane.
Abstract: The operator description of Fourier optics is extended and applied to holography. The existing lens models for ideal holographic processes appear as a self-evident intermediate result; generalization to include apertures, recording-material modulation transfer function, and extended source effects is straightforward. The extended source effect is generally shown to be equivalent to a modification of the actual holographic apertures. The final result is a compact expression for the description of the holographically reconstructed field distribution at an arbitrary plane. A useful, comprehensive list of operator relations is given in two appendixes.

30 citations


Journal ArticleDOI
TL;DR: An interferometer comprising three diffraction gratings and an imaging system is used with spatially and spectrally noncoherent light to produce high fidelity low noise recording of phase- and -amplitude objects.
Abstract: An interferometer comprising three diffraction gratings and an imaging system is used with spatially and spectrally noncoherent light to produce high fidelity low noise recording of phase- and -amplitude objects.

26 citations


Journal ArticleDOI
Eric W. Hansen1
TL;DR: A method of image reconstruction from projections is described which processes the data in polar rather than rectangular coordinates and which does not require back projection.
Abstract: A method of image reconstruction from projections is described which processes the data in polar rather than rectangular coordinates and which does not require back projection. It is based on the decomposition of the object and its shadow (set of projections) into circular harmonics or radial modulators of angular Fourier components. The radial modulators of the object may be reconstructed from those of the shadow using a space-variant system which becomes space-invariant under a coordinate transformation. Experiments using digital and optical implementations are described.

24 citations


Proceedings ArticleDOI
04 Nov 1981
TL;DR: A mathematical filter which improves the contrast response of image intensifiers is derived by inverting the point spread function (PSF) of the system and indicates that a substantial improvement in the contrast ratio can be achieved by this technique.
Abstract: A mathematical filter which improves the contrast response of image intensifiers is derived. The filter is obtained by inverting the point spread function (PSF) of the system. A point spread function which takes into account the spread of light in the image intensi-fier system is proposed using physical arguments. The PSF has two parameters which are the range and the fraction of light which spreads. These two parameters are determined by a least squares fit to the experimentally measured data. The inverse filter is used in the deconvolution of video images. The results indicate that a substantial improvement in the contrast ratio of the system can be achieved by this technique.*

18 citations


Journal ArticleDOI
TL;DR: The image degradation due to Kolmogorov atmospheric turbulence is considered in terms of the time-averaged optical transfer function, point spread function, Strehl ratio, and encircled energy for imaging systems with annular pupils for applications including imaging with mirror telescopes and propagation of obscured laser beams through turbulence.
Abstract: The image degradation due to Kolmogorov atmospheric turbulence is considered in terms of the time-averaged optical transfer function, point spread function, Strehl ratio, and encircled energy for imaging systems with annular pupils. The applications include imaging with mirror telescopes and propagation of obscured laser beams through turbulence. Numerical results are given for obscuration ratios of 0, 0.25, 0.50, and 0.75.

16 citations


Journal ArticleDOI
TL;DR: In this paper, a cylindrical lens was used to achieve a higher image resolution and a smaller degree of color blur for a one-step rainbow holographic process, which relaxes the power requirement of the coherent source.
Abstract: From the point spread function and wavelength spread, the hologram image resolution and color blur for a one-step rainbow holographic process are analyzed. To achieve a higher image resolution and smaller degree of color blur, we proposed the insertion of a cylindrical lens in a one-step rainbow holographic process. We have shown that higher image resolution and a smaller degree of color blur can be obtained by the cylindrical lens technique. Experimental confirmations of the calculated results are also demonstrated. There is another advantage of the cylindrical lens technique, that is, a higher object beam irradiance, for which it relaxes the power requirement of the coherent source.

15 citations


Journal ArticleDOI
TL;DR: The interrelation of several quality parameters for white light imagery is discussed in this article, where the computed distributions of colour for the polychromatic point spread function, line spread function and edge spread function are compared in the presence of chromatic aberrations.
Abstract: The interrelation of several quality parameters for white light imagery is discussed. The computed distributions of colour for the polychromatic point spread function, line spread function, edge spread function and sinusoidal gratings are compared in the presence of chromatic aberrations. It is shown that image quality of practical lenses for white light imagery can be assessed through colour measurements in the line spread function and the OTFs for the tristimulus values.

13 citations


Proceedings ArticleDOI
28 Dec 1981
TL;DR: In this paper, the effects of ripple on image quality are examined with the aid of computer simulations using rotationally symmetric wavefront error models, and through interferometric measurements of a mirror known to have significant surface ripple.
Abstract: Mirror surface ripple acts as a phase grating to diffract light out of the central maximum of the point spread function (PSF), reducing image quality. The effects of ripple on image quality are examined with the aid of computer simulations using rotationally symmetric wavefront error models, and through interferometric measurements of a mirror known to have significant surface ripple. Image quality is evaluated in terms related to the performance requirements of large orbital astronomical telescopes that must perform in both ultra-violet and visible light. Techniques for measuring and specifying ripple are discussed.

11 citations


Journal ArticleDOI
TL;DR: Experimental results obtained with an interferometric imaging technique that utilizes a grating interferometer show substantial improvement in image contrast over that obtained via direct imaging.
Abstract: Imaging through scattering media such as fog is a problem with few known viable solutions. Holographic techniques have been demonstrated successfully in the laboratory, but their usefulness is often limited in field conditions by the requirement of a separate coherent reference beam. In this paper, an interferometric imaging technique that utilizes a grating interferometer is presented. Experimental results obtained with this technique show substantial improvement in image contrast over that obtained via direct imaging.

10 citations


Journal ArticleDOI
TL;DR: Using examples drawn from conventional transmission microscopy, data compression by at least 10 to 12 times (from the original 8 bits per pixel image) and sometimes 20 to 30 times is shown to give acceptable image quality.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the image contrast of a periodic amplitude object in association with periodicity in spatially coherent illumination produced by ultrasonic wave modulation and showed that the most efficient contrast enhancement takes place when the period of the object equals half of the ultrasonic wavelength and the acousto-optic diffraction component of the first order takes a maximum.
Abstract: Imaging of a periodic amplitude object is investigated in association with periodicity in spatially partially coherent illumination produced by ultrasonic wave modulation. Because of this periodicity, the image contrast can be much more enhanced in the presence of the ultrasonic wave than that obtained with a coherent or incoherent imaging system. The most efficient contrast enhancement takes place when the period of the object equals half of the ultrasonic wavelength and the acousto-optic diffraction component of the first order takes a maximum. Theoretical predictions are verified experimentally.

Journal ArticleDOI
TL;DR: The Gerchberg-Saxton algorithm is used as the iterative retrieval technique of the wave aberration with additional information about the type of aberration to retrieve data from the point spread function or the optical transfer function data of the system.
Abstract: This paper describes the digital retrieval method of the wave aberration of an optical system from the point spread function or the optical transfer function data of the system. The Gerchberg-Saxton algorithm is used as the iterative retrieval technique of the wave aberration with additional information about the type of aberration. The usefulness of the proposed method is confirmed by computer simulations. Several problems associated with the retrieval procedure are indicated by elementary experiments with a computer generated hologram as well as by computer simulations.

Journal ArticleDOI
TL;DR: In this article, the spectral magnitude of the image is smoothed by averaging over an ensemble of similar images and the estimate can be extended to degradations such as a defocused lens by thresholding the estimation magnitude to obtain zero crossings and adjusting the phase accordingly.
Abstract: Frequently an image may be blurred by a point spread function whose details are not known exactly. In such a case, it is necessary to estimate the point spread function before deconvolving the blurred image. This paper presents a new technique for estimating a zero phase blurring function when its optical transfer function is smooth. The estimate is obtained by smoothing the spectral magnitude of the image and comparing it to an average magnitude that is also smoothed. The average magnitude is obtained by averaging over an ensemble of similar images. The estimate can be extended to degradations such as a defocused lens by thresholding the estimation magnitude to obtain zero crossings and adjusting the phase accordingly. In particular, this technique can be applied to a circularly symmetric Gaussian blur or a defocused lens with a circular aperture.

Journal ArticleDOI
TL;DR: In this article, a procedure for the iterative deconvolution of X-ray pictures is given and applied to the images taken by the AS & E Inc. and the Aerospace Corporation instruments.
Abstract: Due to the broad wings of the point spread function of the Wolter telescopes used in the Skylab mission for taking X-ray pictures of the solar corona, the images are blurred around bright emission regions. As a result, the maps of temperature and emission measure are distorted. A procedure for the iterative deconvolution of X-ray pictures is given and applied to the images taken by the AS & E Inc. and the Aerospace Corporation instruments.

01 Sep 1981
TL;DR: In this article, the performance of line scan imaging systems as a function of their spatial response (point spread function or modulation transfer function), sensitivity, sampling and quantization intervals, and the statistical properties of a random radiance field was evaluated.
Abstract: Information theory is used to formulate a single figure of merit for assessing the performance of line scan imaging systems as a function of their spatial response (point spread function or modulation transfer function), sensitivity, sampling and quantization intervals, and the statistical properties of a random radiance field Computational results for the information density and efficiency (ie, the ratio of information density to data density) are intuitively satisfying and compare well with experimental and theoretical results obtained by earlier investigators concerned with the performance of TV systems

Journal ArticleDOI
TL;DR: In this paper, a beam integral is used to reduce the image degradation due to the nonzero cross-section of the X-ray beam, which can be obtained from data available in practice.

Journal ArticleDOI
TL;DR: An analog optical implementation of the decoding correlation has the potential of being faster and cheaper when a large volume of data must be processed, which can be the case in nondestructive testing, plasma diagnostics, and some medical and astronomical applications.
Abstract: Coded apertures are used in the high resolution imaging of faint x-ray sources and in their 3-D representations. The technique consists of replacing the pinhole of a pinhole camera with an array of holes which transmits several orders of magnitude more energy. The picture thus obtained needs to be decoded to reconstruct the original object irradiance distribution. The decoding is performed by convoluting the coded image with another array chosen to optimize the system point spread function (PSF). For most arrays, with the exception of Fresnel zone plates (FZP) which can be reconstructed optically, the decoding is done digitally. This approach has great versatility and certainly is the best if the image is furnished by the sensor as an electric signal. For the reconstruction of images recorded on film, however, an analog optical implementation of the decoding correlation has the potential of being faster and cheaper. This is important when a large volume of data must be processed, which can be the case in nondestructive testing, plasma diagnostics, and some medical and astronomical applications.

Journal ArticleDOI
TL;DR: A technique for deriving the point spread function of the blur from such overlapping image pairs has been developed and the resultant point spreadfunction is then applied to restore the blurred images.


Journal Article
TL;DR: In this paper, a point spread function is calculated in terms of the spot diagram obtained through geometrical ray trace or the theory of Kirchhoff diffraction, and the ratio T of the energy passing through the system onto the exit window, to the total energy radiated from a plane target into the entrance pupil is calculated.
Abstract: For infrared optical systems a point spread function is calculated in terms of the spot diagram obtained through geometrical ray trace or the theory of Kirchhoff diffraction Also is calculated the ratio T of the energy passing through the system onto the exit window, to the total energy radiated from a plane target into the entrance pupil Formulas are derived separately for the following different cases: a circular or rectangular ring diffraction pupil, a blur of equivalent intensity distribution or a Gaussian blur, and a circular or rectangular field stop In certain casses T values are given through digital calculation This method of T calculation is useful for any infrared optical systems The table of T values can be applied to the system layout design of infrared instruments and T function used as the merit function of optical systems The calculation of T is very important for diffraction limited systems

Proceedings ArticleDOI
03 Mar 1981
TL;DR: In this article, the authors examine the character of each of the descriptions using a simple model of the telescope response which includes the effects of both figure and scattering and illustrate the conclusions using a numerical example.
Abstract: A description of the performance of an X-ray imaging system can be formulated in several ways. The char-acterization can be given in terms of the point spread function (PSF), the line spread function (LSF), the modulation transfer function (MTF), or the edge spread function (ESF). While the different functions are mathematically related, they do not all emphasize the same performance features equally. In this paper we examine the character of each of the descriptions using a simple model of the telescope response which includes the effects of both figure and scattering and illustrate the conclusions using a numerical example. It is shown that the MTF and ESF are strongly affected by scattering and that the LSF and PSF are affected both by scattering and by the figure of the optics. To assess the spatial resolution of an X-ray imaging system, the PSF description is the most useful and the effects of scattering can be approximately isolated from effects due to the optical figure by using the MTF or ESF,© (1981) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Book ChapterDOI
01 Jan 1981
TL;DR: In this article, the authors defined the COS-B catalogue error boxes taking into account both the PSF and the photon statistics; it is then apparent that the search for candidate counterparts of the GGRS should be carried out inside such boxes, or in their immediate vicinity, and that, for examples, such loose positional coincidences as obtainable by increasing a quoted error radius by 50%, let alone doubling it, are totally unacceptable.
Abstract: The publication of the first (Hermsen et al, 1977) and preliminary second catalogue of the COS-B sources (Wills et al, 1980), has brought to the attention of the astronomical community the new reality of the high-energy Galactic Gamma-Ray Sources (GGRS). It is worth recalling here the definition of such objects, in the COS-B sense: “A GRS is a significant excess of photon counts, compatible with the instrument’s angular resolution, or, more clearly, with the instrument’s Point Spread Function”. This definition of an unresolved (as it is the case for the vast majority of the GGRS) GRS is, to some extent, dependent on the shape of the source spectrum; however a general shape of the PSF for the case of the source associated with 3C273 can be found in Bignami et al, 1980. Naturally, the absolute flux (i.e. the total number of photons) from a source is also important in determining the positional error, especially when usage is made of the cross-correlation method (Hermsen, 1980). Typ ical photon numbers(100 Mev) for GGRS range from 50 to few hundreds. The COS-B catalogue error boxes are defined taking into account both the PSF and the photon statistics; it is then apparent that the search for candidate counterparts of the GGRS should be carried out inside such boxes, or in their immediate vicinity, and that, for examples, such loose positional coincidences as obtainable by increasing a quoted error radius by 50%, let alone doubling it, are totally unacceptable.

01 Jan 1981
TL;DR: In this article, a method for improving the lateral resolution of the B-scan images in the medical applications of ultrasound was proposed based upon a mathematical model of the lateral blurring caused by the finite beam width of the transducers.
Abstract: The objective of this paper is to present a digital method for improving the lateral resolution of the B-scan images in the medical applications of ultrasound. based upon a mathematical model of the lateral blurring caused by the finite beam width of the transducers. This model provides a simple method of applying a recursive scheme for image restoration with fast computation time. The point spread function (P.S.F.) can be measured by the reflective signals after scanning the small pins located along the depth of interest. From the measured P.S.F., one can compute the coefficient matrices of the inverse discretetime dynamic state variable equation of the blurring process. Then, a recursive scheme for deblurring is applied to the recorded B-scan image to improve the lateral resolution. One major advantage of the present recursive scheme over the transform method is in its applicability for the space-variant imaging, such as in case of the rotational movement of transducer. The method is

Journal ArticleDOI
T. Yahagi1
TL;DR: In this article, a method for the design of two-dimensional digital filters to restore blurred images is presented, in which the impulse response (point spread function) which causes the blur of images, is decomposed into a set of one-dimensional impulse responses that are used to design one dimensional digital filters.