Showing papers on "Point spread function published in 1975"
TL;DR: Two correction functions are derived for one- and two-dimensional convolution methods for reconstructing a section image from multiple projections to yield a maximum 'signal-to-noise power ratio' for a given RMS resolution width.
Abstract: Two correction functions are derived for one- and two-dimensional convolution methods for reconstructing a section image from multiple projections. The functions are optimized to yield a maximum 'signal-to-noise power ratio' for a given RMS resolution width, where 'signal power' is the integrated squared line spread function (signal power regarding one-dimensional position information per count) and 'noise power' is the variance of the image density at the centre of a locally uniform source. The point spread function of the reconstructed image is Gaussian, and the standard deviation of noise associated with a locally uniform image is found to be proportional to D-32/, where D is the RMS resolution width. The autocovariance function for uniform noise is also given.
59 citations
TL;DR: In this article, the power spectrum of a turbulence-degraded image of a point source as a function of exposure time is derived based on the near-field Rytov-Kolmogorov approximations and the Taylor hypothesis.
Abstract: Mathematical expressions are obtained for the power spectrum of a turbulence-degraded image of a point source as a function of exposure time. Calculations are based on the near-field Rytov–Kolmogorov approximations and the Taylor hypothesis. Comparisons with available data are satisfactory.
39 citations
TL;DR: Analysis of an x-ray imaging system employing ellipsoid and hyperboloid mirrors that are confocal and coaxial indicates that spatial resolution of 1-3 microm can be obtained.
Abstract: Analysis of an x-ray imaging system employing ellipsoid and hyperboloid mirrors that are confocal and coaxial indicates that spatial resolution of 1–3 μm can be obtained. The useful field of view is hundreds of microns, and the collecting solid angle is at least 103 times that of a pinhole camera. The instrument has application to the diagnostics of laser-pellet interactions.
34 citations
TL;DR: In this article, the second-order statistics of time-averaged speckle were investigated for the probability density function of intensity, with two forms of solution being obtained, one exact solution and the other an approximate solution.
27 citations
TL;DR: A technique is described for recording representations of space-variant optical systems as volume holograms, where the transfer-function holographic representations obtained are then placed in the Fourier plane of a coherent optical processor for playback.
Abstract: A technique is described for recording representations of space-variant optical systems as volume holograms. The transfer-function holographic representations obtained are then placed in the Fourier plane of a coherent optical processor for playback. Due to the space-variant nature of the systems represented, the input plane of the system to be represented holographically is spatially sampled. As a result, the volume hologram medium actually contains a number of holograms that have been angle multiplexed to avoid interference problems. Limitations associated with the thickness of the recording medium are calculated for imaging systems, and experimental results are presented for one lens and two lens magnifiers.
26 citations
TL;DR: For linear transfer conditions and objects with isotropic statistics, both the sharpness of the point spread function and its departure from rotational symmetry show up in the shape of the autocorrelation peak of the electron micrograph.
Abstract: For linear transfer conditions and objects with isotropic statistics, both the sharpness of the point spread function and its departure from rotational symmetry show up in the shape of the autocorrelation peak of the electron micrograph. It is therefore suggested that this function be used for interactive or automatic focusing and stigmating of instruments with online digital image readout. Model computations suggest that this method works satisfactorily at reduced levels of exposure.
22 citations
01 Feb 1975
TL;DR: In this article, the authors used the optical transfer function (OTF) of the focal spot to measure the pinhole image size and then used the first zero spatial frequency of the OTF for the determination of an equivalent uniform LSF.
Abstract: It is well known that the x-ray intensity distribution of the focal spot can significantly affect radio-logic images, for example, blood vessel images in angiography (Refs.1, 2). For an accurate evaluation of the effect of this distribution on vessel images, it is essential to use the line spread function (LSF), the point spread function (PSF), or the optical transfer function (OTF) of the focal spot. However, for many years it has been common practice to describe the focal spot by its size, which is looked upon as a single figure of merit for the x-ray intensity distribution of the focal spot. Two methods are relatively well known; one is to measure the pinhole image size by a subjective judgment (Ref.3), and the other is to use the first-zero spatial frequency of the OTF for the determination of an equivalent uniform LSF (Ref.4).
18 citations
TL;DR: In this article, an expression for the information capacity of the optical-mechanical line-scan imaging process is derived, which includes the effects of blurring of spatial detail, photosensor noise, aliasing, and quantization.
Abstract: An expression for the information capacity of the optical-mechanical line-scan imaging process is derived, which includes the effects of blurring of spatial detail, photosensor noise, aliasing, and quantization. Both the information capacity for a fixed data density and the information efficiency (i.e., the ratio of information capacity to data density) exhibit a distinct single maximum when displayed as a function of sampling rate, and the location of this maximum is determined by the system frequency response shape, SNR, and quantization interval.
17 citations
TL;DR: In this article, the second-order statistics of time-averaged speckle were investigated for the case of speckles formed in the Fraunhofer plane when an aperture was moved over the surface of a uniformly illuminated diffuse object.
15 citations
TL;DR: In this article, the optical deblurring of electron images recorded under linear phase or amplitude conditions was investigated using binary fillers of the Lohmann and Paris typc, and the results encourage further effort.
Abstract: Binary fillers of the Lohmann and Paris typc are considered for the optical deblurring of electron images recorded under linear phase or amplitude conditions. Filter performance is tested indirectly by mean of simulated point spread function, and directly by the deblurring of an lIndcrfocused micrograph of ferritin. The results encourage further effort.
9 citations
01 Jan 1975
TL;DR: It has been shown that if one accurately measures the relative phase variation across the transducer due to the skull, the point spread function can be calculated to a close approximation.
Abstract: In spite of many previous research efforts, B-mode echoencephalography is not used clinically for adults because of the poor quality of the images obtained with current, techniques. The intervening presence of the skull results in low sensitivity, reverberations, distortions in the range and lateral dimension, and, most importantly, poor lateral resolution (White, 1970). Lateral resolution, which can be described by the system point spread function (PSF), is a function of the relative phase variation introduced across the transducer aperture by the presence of the skull. A technique has been described (Phillips, et al., this volume) whereby this phase aberration can be measured by a secondary transducer and compensated for in a phased array imaging system, thus restoring the PSF to its unaberrated condition. An alternate technique will be described here which requires no such a priori knowledge of the skull phase variation. This is accompushed by optimizing the transducer frequency and size, and by signal processing the returning echoes. It has been shown (Phillips, et al., this volume) that if one accurately measures the relative phase variation across the transducer due to the skull, the point spread function can be calculated to a close approximation. A simple but accurate model of the skull predicts that the phase variation, \( \Delta \phi \), is a linear function of skull thickness, y, and ultrasound frequency, f.
Journal Article•
TL;DR: In this article, it was shown that a weak phase object imaged by an electron microscope within the presence of instabilities of the lense currents and the acceleration voltage, fluctuating electromagnetic field, can be reconstructed from the intensity distribution in the image plane.
01 Jan 1975
TL;DR: In this article, it was shown that a weak phase object imaged by an electron microscope within the presence of instabilities of the lense currents and the acceleration voltage, fluctuating electromagnetic field, can be reconstructed from the intensity distribution in the image plane.
Abstract: It is shown that a weak phase object imaged by an electron microscope within the presence of instabilities of the lense currents and the acceleration voltage, fluctuating electromagnetic field, can be reconstructed from the intensity distribution in the image plane Perfectly incoherent illumination of the object is assumed and the influence of the energy spread of the illuminating wave on the point spread function of the microscope is rigorously taken into account
10 Jun 1975
TL;DR: In this article, the Fourier transform approach is utilized to calculate the effective point spread function for these processes in the time domain, and a simple modification of the Crowell and Labuda model suggested by these results is presented.
Abstract: The MTF degradation due to lateral diffusion is calculated for a back illuminated CCD imager for typical device parameters. The discrete nature of the CCD and finite size of the photosensitive elements result in an additional MTF degradation. The Fourier transform approach is utilized to calculate the effective point spread function for these processes in the time domain. Experimental data are presented on the point spread function for a three phase, double level anodized aluminum 160 x 100 thinned and back illuminated CCD imager and compared with the theoretical results. A simple modification of the Crowell and Labuda model suggested by these results is presented.
TL;DR: The experimental value of the limit of resolution adopted by Commission International d'Optique, appears to be the limit allowed by the Shannon-Nyquist criterion in the discrete structure of the retina.
TL;DR: In a one-dimensionally-scanned optical system, the out put signal is obtained by convolving the image with the de tector function in the scanned direction and integrating the convolvedfunction in the nonscanned direction.
Abstract: In a one-dimensionally-scanned optical system, the out put signal is obtained by convolving the image with the de tector function in the scanned direction and integrating the convolved function in the nonscanned direction. The ef fects of object and detector sizes on the spatial resolution are shown for a diffraction-limited optical system. The de pendence on the nonscanned direction and thus the inte gration may be omitted when either the object or detector size is large compared with the blur radius. In an optical imaging system, the image I (x,y) can be shown to be related to the object function, 0 (x,y), and point spread function, P (x,y), as:
01 Dec 1975
TL;DR: In the ideal case the output In(x,y) of a microdensitometer can be considered as a true image, i.e. the final product of a linear optical system "pointed" at an incoherent object brightness distribution in the sky or elsewhere as discussed by the authors.
Abstract: In the ideal case the output In(x,y) of a microdensitometer can be considered as a true image, i.e. the final product of a linear optical system “pointed” at an incoherent object brightness distribution Io(x,y) in the sky or elsewhere. Since a photographic emulsion is a non-linear storage element for intensities (apart from noise and granularity effects), and since the linearity of the scanning system is not a matter of course, this final link in such an optical chain is the weakest.
TL;DR: An analytical expression for the intensity ditribution in the Fraunhofer diffraction image of a point source formed by an optical system with slit in presence of linear image motion was derived in this article.
Abstract: An analytical expression has been derived for the intensity ditribution in the Fraunhofer diffraction image of a point source formed by an optical system with slit in presence of linear image motion. Illustrative intensity distributions have been plotted.