Showing papers on "Optical transfer function published in 1977"
TL;DR: In this article, the authors measured the contrast sensitivity of the human eye with sinusoidal grating targets of various spatial frequencies and found that the shape of the contrast-sensitivity function and its absolute values show good agreement among normal subjects, but the most interesting properties of this function cannot be attributed to the optics of the eye, but must be understood in terms of the image processing activities of the visual pathways.
Abstract: Like the modulation transfer function of man-made imaging devices, the contrast sensitivity of the human eye can be measured with sinusoidal grating targets of various spatial frequencies. Criterion-free psychophysical methods permit us to regard the contrast sensitivity as a direct measure of the subject's visual performance, independent of subjective factors. Under these conditions, not only the shape of the contrast-sensitivity function but also its absolute values show good agreement among normal subjects. However, the most interesting properties of this function cannot be attributed to the optics of the eye, but must be understood in terms of the image-processing activities of the visual pathways. The contrast-sensitivity function varies with the size, brightness, motion and flicker of the test target, with the adaptive state of the subject's retina, and with his eye-movements. Most of these effects can be explained in terms of known neurophysiology.
261 citations
TL;DR: In this paper, an active optical imaging system capable of correcting optical wave-front errors in real time at frequencies in the kilohertz range was developed, which can be applied to apertures of any size; experimental results were shown for a system with 21 correction zones.
Abstract: We have developed an active optical imaging system capable of correcting optical wave-front errors in real time at frequencies in the kilohertz range. Wave-front errors due to atmospheric turbulence in the propagation path, as well as optical figure aberrations and wave-front errors due to mechanical and thermal changes may be compensated. The system used an ac shearing interferometer, a parallel analog data processor, and a monolithic piezoelectric active mirror arranged in a closed-loop configuration. This compensation system can be applied to apertures of any size; experimental results are shown for a system with 21 correction zones.
250 citations
98 citations
TL;DR: The two-dimensional modulation transfer function [MTF(vx, vy)] has been determined for the EMI CT head scanner by measuring the point spread function (PSF) in different locations in the field of view by scanning a fine wire supported perpendicular to the tomographic slice.
Abstract: The two-dimensional modulation transfer function [MTF(vx, vy)] has been determined for the EMI CT head scanner by measuring the point spread function (PSF) in different locations in the field of view. This PSF was obtained by scanning a fine wire supported perpendicular to the tomographic slice. Based on these MTFs, the resolving power of the EMI scanner was found to be 3.1 line pairs/cm. Our results also verify the symmetry of the system response and the uniformity of the system resolution.
96 citations
27 Dec 1977
TL;DR: In this article, an equation for calculating the theoretical attenuation profile optical transfer function (OTF) from the geometrical dimensions of the system was derived and the results were presented.
Abstract: The geometrical limitation of the spatial resolution inherent in a CT scanner has been analyzed. In order to assess this limitation, an equation for calculating the theoretical attenuation profile optical transfer function (OTF) from the geometrical dimensions of the system was derived. Four commercially available CT units were studied which are representative of the three basic design types in use. For each unit the OTF was calculated and the results are presented. Using this information in conjunction with the pixel size and data sampling frequency of the attenuation profiles, an analysis of the factors limiting the spatial resolution of each unit was made. In addition, subtle effects on the image quality of a scan due to the geometry of the data-taking mechanics are discussed and correlated with the observations of experimental comparisons. A suggestion is made for the optimal design of a CT unit that will encompass the conclusions of this analysis.
41 citations
TL;DR: In this article, the theory of short-term average modulation transfer function developed by Fried is extended by considering the correlation between the turbulence-induced phase distortion and the residual phase aberrations after adaptive phase compensations.
Abstract: The theory of short-term average modulation transfer function developed by Fried is extended by considering the correlation between the turbulence-induced phase distortion and the residual phase aberrations after adaptive phase compensations. Calculation of the optical resolution shows that the original approximation is valid for the normalized lens diameter D/r0 less than 4.0; conversely, for D/r0 greater than 4.0 the optical resolution becomes arbitrarily large because the MTF is unrealistically overcorrected at high spatial frequencies. The extended formulation is then applied to the cases with higher-order phase compensations such as focus and astigmatism. The peak optical resolution occurs at larger values of D/r0 when the higher-order corrections are included.
38 citations
35 citations
TL;DR: Image quality, resolution and sensitivity of a scintillation camera equipped with various collimators have been investigated using high purity 123I and the modulation transfer function evaluated from the line spread functions shows a sudden drop at low frequencies for high resolution collimator due to their high degree of septa penetration.
Abstract: Image quality, resolution and sensitivity of a scintillation camera equipped with various collimators have been investigated using high purity 123I. Pulse height distributions of 123I from a thyroid phantom partly in air and partly immersed in water demonstrated the substantial septa penetration of the 440 and 529 keV gamma rays of 123I with high resolution collimators. Line spread functions were recorded and the modulation transfer function was evaluated from them. The two concepts of 'figure of merit' also used were QB=Sa mod MTF mod 2, where Sa is the plane sensitivity and QC=S2/(S+2B), where S is the true signal from the object and B is the total background or noise due to septa penetration and scatter.
29 citations
TL;DR: A simple analog technique for extracting signals from noise is discussed in this paper, where techniques for measuring and interpreting MTF (modulation transfer function), limiting resolution, temporal and spatial noise, image spreading, and image lag are discussed.
Abstract: Charge coupled imagers present special problems not encountered with beam-scanned sensors. This paper describes some of the instrumentation, procedures, and analyses used to evaluate charge coupled imagers. A simple analog technique for extracting signals from noise is discussed. Techniques are given for measuring and interpreting MTF (modulation transfer function), limiting resolution, temporal and spatial noise, image spreading, and image lag. Effects peculiar to CCDs (charge coupled devices) and CIDs (charge injection devices), such as aliasing and image smearing, are discussed.
26 citations
TL;DR: It is shown that the point spread function and optical transfer function of geometric unsharpness at any arbitrary field position can be derived from those at the central beam position.
Abstract: The basic theory of field characteristics is discussed. It is shown that the point spread function and optical transfer function (OTF) of geometric unsharpness at any arbitrary field position can be derived from those at the central beam position. At all locations in the radiation field, the OTF in a direction parallel to the x-ray tube cathode--target axis does not depend on the field position X, which is perpendicular to the to the tube axis, whereas the OTF in a perpendicular direction does not depend on the field position Y, which is parallel to the tube axis. The theoretical result is used to demonstrate the field characteristic of the uniform, square focal spot. (AIP)
26 citations
TL;DR: The quantitative data are used to determine aberration tolerances for instruments that are designed for specific visual tasks and that employ simple targets similar to those investigated, and indicate that the eye accomodates of a "best focus" when spherical aberration and astigmatism are present in the instrument.
Abstract: The effects of aberrations on images formed by a total system, including the eye, are assessed in terms of modulation threshold, grating detectability, and modulation transfer functions. The effects of approximately one and two waves of third-order spherical aberration, coma, and astigmatism on the total system modulation transfer function are investigated using three-bar resolution targets and Ronchi rulings in two separate psychophysical experiments. The results of both experiments indicate that the experimentally determined system modulation transfer function is closely approximated by the theoretically calculated modulation transfer function of the total system optics (dioptrics included) in the presence of instrument aberrations. The data indicate that the eye accomodates to a “best focus” when spherical aberration and astigmatism (but not coma) are present in the instrument. The quantitative data are used to determine aberration tolerances for instruments that are designed for specific visual tasks and that employ simple targets similar to those investigated.
TL;DR: In this paper, a simple condition is shown to be necessary and sufficient to suppress edge-ringing in optical imaging, which is valid in the presence of aberrations and apodization, and for all cases of (spatially stationary) partially coherent illumination.
Abstract: A simple condition is shown to be necessary and sufficient to suppress edge-ringing in optical imaging. This criterion is valid in the presence of aberrations and apodization, and for all cases of (spatially stationary) partially coherent illumination. The edge-ringing tendencies of an optical system may be assessed through the use of two new performance functions which form a Fourier-transform pair. One of these performance functions is related to the ‘transmission cross-coefficient’ which appears in the theory of partially coherent imaging. In the coherent limit this performance function reduces to the amplitude transfer function (pupil function), and in the incoherent limit it reduces to the Optical Transfer Function (OTF). The use of this performance function for the general assessment of partially coherent imaging systems is suggested.
TL;DR: A mathematical model to predict the system performance for both one-step and two-step copying procedures is developed, and numerous computer results of parameter variation are given.
Abstract: The halftone screen process for obtaining nonlinear functions with coherent optical systems utilizes a preiprocessing step with an ideally hard-clipping binaryinput recording medium. This paper analyzes in detail the effects of using film or other media with finite gamma and saturation density. A mathematical model to predict the system performance for both one-step and two-step copying procedures is developed, and numerous computer results of parameter variation are given. It is found that nonlinear functions with threshold or jump characteristics are the most sensitive to the nonideal effects. A precompensation technique allowingnonideal copy film to be used with minimum degradation of the transfer characteristic is presented, and an algorithm for calculating compensated halftone cell shapes is given, with examples.
26 Sep 1977
TL;DR: In this article, a technique that evaluates the narcissus effect in terms of narcissus equivalent temperature difference (NARCAT) has been developed and programmed for the computer, and computer results for several infrared optical scanning systems indicate that predicted and measured values of NARCAT agree well.
Abstract: In a typical infrared optical scanning system, the surface temperature of the detector is usually much less than the ambient. The narcissus effect occurs when the detector, through unintended reflections off internal lens surfaces, sees sources at temperatures other than the background ambient. These sources usually are reflections of the detector itself, hence the term narcissus. The resulting display shows abrupt changes in the background radiation as a function of field position. A technique that evaluates the narcissus effect in terms of narcissus equivalent temperature difference (NARCAT) has been developed and programmed for the computer. Computer results for several infrared optical scanning systems indicate that predicted and measured values of NARCAT agree well. The theory is based on the principle that radiance along any geometrical ray bundle does not vary. 1 The narcissus-induced variation of this radiance is found to be the arithmetic product of three factors, viz., (1) image-forming, (2) surface spectral reflec-tance, and (3) temperature difference. Therefore, to suppress the narcissus effect, one simply minimizes these factors. Examples illustrating both the computational approach and the suppression techniques are given.
TL;DR: A phenomenological model of the acoustooptic modulator is proposed, which shows that the temporal response of the deflected light power is a quadratic invariant function of the video signal amplitude.
Abstract: The Green's function model of the acoustooptic modulator proposed by E. I. Gordon et al. is reformulated in Fourier transform space to simplify the mathematics and to underscore the physics. Numerical studies of response to sinusoidal video signals and to square pulse trains indicate that the modulator can be approximated by a linear invariant model with a suitably scaled Gaussian impulse response. An angular scattering window analogy is proposed to explain the characteristics of the modulator.
Journal Article•
TL;DR: The procedures for recording of the LSF and calculation of the MTF are performed independently of a computer, allowing nuclear medicine laboratories without access to a computer to incorporate MTF studies into their quality-assurance programs.
Abstract: This article describes a method for the rigorous calculation of modulation transfer function (MTF) of a collimated scintillation detector using a programmable pocket calculator. The calculation utilizes a normalized discrete Fourier transform (DFT) of the line spread function (LSF) including real and imaginary terms. A method is described for recording the LSF using an Anger camera and multichannel analyzer (MCA). The procedures for recording of the LSF and calculation of the MTF are therefore performed independently of a computer, allowing nuclear medicine laboratories without access to a computer, allowing nuclear medicine laboratories without access to incorporate MTF studies into their quality-assurance programs. The results obtained using the pocket calculator were compared with those using a PDP-12 minicomputer. The pocket calculator was slightly more accurate, since it does not suffer from the round-off errors of the PDP-12. The time required to plot an 11-point MTF curve using the pocket calculator was 5 min, using the PDP-12 0.5 min.
TL;DR: In typical experiments with narrow field objects, it is shown that the zone plate behaves like a diffraction-limited lens, the gain in resolution is noticeable as the wavelength decreases, the use of the third-order focus improves the resolution of the system, and under certain conditions the depth of field can be increased without loss of resolution.
Abstract: The feasibility of optical systems for short wavelength radiations ranging from the near uv to soft x rays is supported by theoretical and experimental arguments. The major problem of absorption of these radiations by materials has been overcome in the near and middle uv by using the lens properties of a Fresnel zone plate generated on a thin self-supporting film. In typical experiments with narrow field objects, it is shown that the zone plate behaves like a diffraction-limited lens, the gain in resolution is noticeable as the wavelength decreases, the use of the third-order focus improves the resolution of the system, and under certain conditions the depth of field can be increased without loss of resolution. The chromatic aberrations of the zone plate are not restrictive for a large number of applications.
TL;DR: A method to study the loss of resolution of radiological images caused by patient motion is presented and the line spread function of a pattern of motion can be generated from the image of a long, narrow moving slit.
Abstract: A method to study the loss of resolution of radiological images caused by patient motion is presented. Optical transfer functions (OTF) are computed for motion with uniform velocity and with simple harmonic oscillation. The line spread function (LSF) of a pattern of motion can be generated from the image of a long, narrow moving slit. Once the LSF is known the OTF of the motion can be obtained by Fourier transform.
TL;DR: In this paper, the Fourier reconstruction algorithm applied to phantom radionuclide sources of nuclear medicine is discussed in relation to the angular sampling of frequency space and investigated using coherent optical techniques.
Abstract: Optical and digital processing of tomographic data is presented and discussed in the context of a Fourier reconstruction algorithm applied to phantom radionuclide sources of nuclear medicine. The point spread function of the reconstruction process is discussed in relation to the angular sampling of frequency space and investigated using coherent optical techniques. Approximations due to gammaray attenuation in the source and the non-stationarity of the point spread function of the detector system are also presented.
TL;DR: This first part of a two-part article on the design and analysis of rotating prism compensators is theoretical and provides an overview on the nature of the image in simple compensators while explaining the principles upon which complex designs are based.
Abstract: This first part of a two-part article on the design and analysis of rotating prism compensators is theoretical and provides an overview on the nature of the image in simple compensators while explaining the principles upon which complex designs are based. Some new schemes, consistent with available optical materials and engineering techniques, are developed that offer significantly improved image quality. (The second part, in preparation by the authors, addresses the specification and computer analysis of optical design, with particular emphasis on predicting the effective modulation transfer function in a high-speed rotating prism camera. A new wide-angle lens, based on theoretical considerations, was designed for a conventional 70mm camera. Measurements with the finished lens are compared with prediction and existing lenses. The computer performance of a new compensation scheme is compared with a conventional rotating prism compensator.)
28 Dec 1977
TL;DR: In this article, a review of the pertinent fundamentals of optics is presented, including concepts of incoherent, coherent, and partially coherent light, propagation of coherent light; diffraction and interference; Fraunhofer diffraction as a Fourier transformation; spatial frequency concepts; properties of image formation, amplitude impulse response, intensity impulse response and the optical transfer function.
Abstract: This tutorial consists of a review of the pertinent fundamentals of optics: concepts of incoherent, coherent, and partially coherent light; propagation of coherent light; diffraction and interference;Fraunhofer diffraction as a Fourier transformation; spatial frequency concepts; properties of image formation, amplitude impulse response, intensity impulse response, and the optical transfer function; simultaneous optical Fourier transformation and image formation; simple spatial filtering operations.
Journal Article•
01 Aug 1977
TL;DR: In this paper, the results of such measurements, made by the Air Force Avionics Laboratory, on two cameras, A Wild RC-8 R-10 and a Zeiss RMK AR 15/23, were compared with those made at the “Physikalisch-Technische Bundesanstalt” in West Germany.
Abstract: The success of using the Modulation Transfer Function (MTF) in characterizing image location and image quality for aerial mapping cameras is dependent upon the ability to successfully and accurately measure this quantity. This paper will present the results of such measurements, made by the Air Force Avionics Laboratory, on two cameras, A Wild RC-8 R-10 and a Zeiss RMK AR 15/23. MTF measurements were made on-axis and at 10°, 20°, 30°, 40° and 45° for both radial and tangential orientations. Through-focus runs at each field position were conducted. All measurements were made in filtered green light ( λ = 546.1 nm). The results are compared with those made at the “Physikalisch-Technische Bundesanstalt” in West Germany.
01 Jun 1977
TL;DR: The modulation transfer function of radiologic imaging systems is commonly obtained by determining the line spread function (LSF) of the system and computing its Fourier transform and an expression for the MTF of a finite rectangular slit is derived.
Abstract: The modulation transfer function of radiologic imaging systems is commonly obtained by determining the line spread function (LSF) of the system and computing its Fourier transform. Ideally, LSF should be obtained with infinitesimally narrow slits. The use of finite slits for obtaining the LSF is analyzed theoretically. An expression for the MTF of a finite rectangular slit is derived. Slit width correction of observed MTF is discussed as well as the correction for any generalized slit configuration.
18 Nov 1977
TL;DR: In this article, the optical transfer function (OTF) of the atmosphere has been measured over the ocean for four wavelengths from visible to far IR, using laser sources and a slit scanning telescope.
Abstract: The optical transfer function (OTF) of the atmosphere has been measured over the ocean for four wavelengths from visible to far IR, using laser sources and a slit scanning telescope. The effects of diffraction, finite slit width, and aberrations have been removed by digital Fourier processing. The shapes of the curves of long term average OTF, and the image-centered (tracked) OTF, as well as the magnitude of the wander variance, all agree well with a theoretical model by Fried. Comparisons of the path-integrated values of Cn 2 , obtained from the OTF, with the path-integrated values of Cn obtained from CT 2 , indicate that, for nonuniform Cn2, the weighting of Cn 2 as a function of position on the path, behaves as predicted. This weighting heavily emphasizes the part of the path nearest the telescope for imaging devices, whereas scintillation emphasizes the path center. The weighting that applies to imaging devices also applies to beam-forming or projection sys-tems, with the heavily emphasized part near the projection optics. Measurement with a scanning telescope thus yields directly the properly weighted value for such systems.
TL;DR: It is shown that this technique is mathematically equivalent to the multiple-sine-slit microdensitometer (MSSM) MTF measurement approach and a method for extending the OMF to high spatial frequencies is discussed.
Abstract: A modulation transfer function (MTF) measuring technique is described that employs the optical matched filter (OMF). It is shown that this technique is mathematically equivalent to the multiple-sine-slit microdensitometer (MSSM) MTF measurement approach. Similarities and differences in the implementation of the two methods are discussed. Both theoretical and experimental matched filter results are investigated. A method for extending the OMF to high spatial frequencies is discussed.
Journal Article•
12 Oct 1977
TL;DR: In this paper, the authors describe the method which is used at RAE Farnborough, to carry out laboratory evaluations of thermal imaging systems, and the major performance parameters which are measured are Minimum Resolvable Temperature Difference (MUD), Minimum Detectable Temperature Difference(MDTD), Modulation Transfer Function (MTF) and Signal Transfer Function(SiTF).
Abstract: This paper describes the method which is used at RAE Farnborough, to carry out laboratory evaluations of thermal imaging systems. The major performance parameters which are measured are Minimum Resolvable Temperature Difference (MUD), Minimum Detectable Temperature Difference (MDTD), Modulation Transfer Function (MTF) and Signal Transfer Function (SiTF). The reasons for choosing these parameters are discussed, and a description is given of the apparatus and the techniques which are used for the measurements.
08 Dec 1977
TL;DR: In this article, a new holographic implementation of a sampling technique permits straightforward representations of two dimensional space-variant optical systems, where the set of sample transfer functions required for the representation is sequentially recorded on a single holographic plate by utilizing a diffuser to produce phase-coded reference beams.
Abstract: A new holographic implementation of a sampling technique permits straightforward representations of two dimensional space-variant optical systems. The set of sample transfer functions required for the representation is sequentially recorded on a single holographic plate by utilizing a diffuser to produce phase-coded reference beams. The phase coding operation then acts to suppress crosstalk between the stored holograms when they are played back simultaneously. Because this approach does not depend on volume effects in the recording medium in an essential way, the holograms can either be produced digitally or optically. Basic concepts and the results of experimental investigations are presented and discussed.© (1977) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.