Showing papers on "Contrast transfer function published in 1996"
TL;DR: An objective, quantitative, and general algorithm to improve the fidelity of three-dimensional reconstructions made from electron micrographs while at the same time filtering much of the noise present in the recorded data is developed.
119 citations
TL;DR: It is shown that optimal resolution can be restored to a spherically aberrated image by constrained, iterative deconvolution, as long as the spherical aberration in the point spread function used for deconvolved image matches the aberrations in the image reasonably well.
Abstract: The wavelength dependence of the incoherent point spread function in a wide-field microscope was investigated experimentally. Dispersion in the sample and optics can lead to significant changes in the point spread function as wavelength is varied over the range commonly used in fluorescence microscopy. For a given sample, optical conditions can generally be optimized to produce a point spread function largely free of spherical aberration at a given wavelength. Unfortunately, deviations in wavelength from this value will result in spherically aberrated point spread functions. Therefore, when multiple fluorophores are used to localize different components in the same sample, the image of the distribution of at least one of the fluorophores will be spherically aberrated. This aberration causes a loss of intensity and resolution, thereby complicating the localization and analysis of multiple components in a multi-wavelength image. We show that optimal resolution can be restored to a spherically aberrated image by constrained, iterative deconvolution, as long as the spherical aberration in the point spread function used for deconvolution matches the aberration in the image reasonably well. The success of this method is essentially independent of the initial degree of spherical aberration in the image. Deconvolution of many biological images can be achieved by collecting a small library of spherically aberrated and unaberrated point spread functions, and then choosing a point spread function appropriate for deconvolving each image. The co-localization and relative intensities of multiple components can then be accurately studied in a multi-wavelength image.
108 citations
TL;DR: In this article, the authors proposed a phase-retrieval method for the retrieval of the exit-plane wave function in high-resolution transmission electron microscopy using off-axis electron holography and focal series reconstruction.
100 citations
TL;DR: A graphical user interface is implemented in an X-window/UNIX environment to compute and display the incoherently averaged Fourier transforms of electron images of single particles embedded in ice and the simulated contrast transfer function with or without envelope functions.
93 citations
TL;DR: A direct method for retrieval of the projected potential from a single HREM image of a thin sample is presented, and both out-of-focus and astigmatic images can be restored and a further improvement achieved by imposing the symmetry exactly.
58 citations
TL;DR: In this paper, a set of programs is developed for determining the defocus and astigmatism of an electron image from the modulation of the Fourier transform due to the contrast transfer function (CTF) of a microscope.
50 citations
Patent•
18 Apr 1996TL;DR: In this paper, a charge coupled device X-ray sensor and camera capable of imaging with high modulation transfer function for high resolution is used to achieve high resolution by simultaneously measuring the modulation transfer functions of x-ray and visible images while imaging the target or the scene.
Abstract: Charge coupled device X-ray sensor and camera capable of imaging with high modulation transfer function for high resolution. The high resolution is achieved by a method of simultaneously measuring the modulation transfer functions of x-ray and visible images while imaging the target or the scene. Then, by using the point spread function and measured MTFs at various spatial frequencies to calculating spatial frequency dependent correction table or correction parameters. This correction is applied to the raw image of the target inside a workstation using a software embodiment of the correction algorithm. The high precision, multi-spatial frequency patterns that are used in x-ray image correction are provided on the sensor, the scintillator screen and the fiber optic face plate of a sensor device to enable the user of the workstation to measure the modulation transfer functions (contrast transfer function) in the horizontal, vertical and in oblique orientations at several spatial frequencies.
25 citations
TL;DR: In this paper, the origin of multiple solution in maximum entropy image deconvolution has been analyzed for simple crystal structures and the entropy-defocus curves contain two kinds of peaks, sharp peaks originate in the loss of at least one diffracted beam due to the defined threshold for contrast transfer function.
20 citations
05 Feb 1996
TL;DR: In this article, the optical transfer function of an incoherent imaging system is modified such that it is nearly invariant to misfocus and contains no zero values, and a digital filtering of the resulting image restores the image to near diffraction limited spatial resolution.
Abstract: We modify the optical transfer function of an incoherent imaging system such that it is nearly invariant to misfocus and contains no zero values. Digital filtering of the resulting image restores the image to near diffraction limited spatial resolution. A system that is insensitive to misfocus is also insensitive to some lens aberrations. Consequently, the approach of combining optical and digital signal processing system extends the normal aberration balancing of lens design to include those aberrations that can be reduced by digital signal processing, such as spherical aberration.
12 citations
TL;DR: In this article, the image formation in paraboloidal reflectors with Seidel (fourth order) aberrations, particularly the spherical aberration, curvature of field aberration and distortion aberration was studied.
9 citations
TL;DR: In this article, the limitations of hollow-cone imaging are outlined and optimum imaging parameters are determined, assuming a coherent electron beam, and the effects of limited coherence of the electron beam upon HCI are discussed, and experimentally obtained images with a Philips CM30 ST electron microscope are shown.
TL;DR: In this paper, a detailed analysis of bar/space pattern methods used in the contrast transfer function (CTF) calculation of linear solid-state X-ray sensitive detectors (LD) is presented.
Abstract: This paper presents a detailed analysis of bar/space pattern methods used in the contrast transfer function (CTF) calculation of linear solid-state X-ray sensitive detectors (LD) The analysis presented centres on the effect of cell aperture on LD response as well as on the measurement of the LD's CTF along its main axis Various theoretical simulations are designed to obtain a better understanding of the behaviour of the LD The simulation results are also compared with the experimental CTF measurements
11 Apr 1996
TL;DR: In this paper, the authors compared the characteristics of a very high resolution film/screen system for mammography with those of a conventional mammography system using Wiener spectra, MTF and sensitometry.
Abstract: The characteristics of a novel, very high resolution film/screen system for mammography are compared with those of a conventional film/screen system for mammography. The image quality characteristics of these systems are measured in terms of Wiener spectra, MTF and sensitometry. These parameters then determine the signal-to-noise (SNR) transfer properties of these systems in terms of the contrast transfer function (CTF), the detective quantum efficiency (DQE) and the noise equivalent quantum efficiency (NEQ). Furthermore, the SNR transfer characteristics are modeled and rationalized by means of the light scattering properties of the intensifying screens and the scintillation spectra of the phosphor. The new system displays superior SNR properties ascribable to its x-ray absorption attributes and the light scattering properties of the phosphor coating.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
01 Jan 1996
TL;DR: In this article, the authors discuss the principle of bright field imaging and a drawback of the bright field technique and present the graphical presentation of bright-field hollow-cone transfer functions at optimum focus for various values of Γ 2.
Abstract: This chapter discusses the principle of bright-field imaging and a drawback of the bright-field technique. It reviews the bright-field image formation in terms of transfer functions. The chapter explains the phase contrast and amplitude contrast transfer function and discusses the spectral distributions of the illumination. It further focuses on the imaging of weakly scattering specimens in axial bright-field imaging conditions and presents the graphical presentation of bright-field hollow-cone transfer functions at optimum focus for various values of Γ 2 . The linear transfer theory depends essentially on the assumption that the unscattered beam is considerably stronger than the scattered beam, but this may well not be true for crystalline specimens, where the electrons are concentrated in spots in the back-focal plane of the objective.
TL;DR: In this paper, a new objective lens design for an electron beam probe was reported, which was a sharp (50 meV) secondary electron transfer function with low aberration coefficients for the primary beam.