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modulation transfer-functions OF LOW-VISION AIDS - COMPARISON WITH SPATIAL-FREQUENCY REQUIREMENTS IN LOW VISION

APPLIED OPTICS 1992年第19期31卷 3637-3645页

作者： LEAT, SJ RUMNEY, NJ UNIV WALES COLL CARDIFF DEPT OPTOMETRYCARDIFF CF1 3YJWALES

modulation transfer functions (MTF's) of 26 low-vision aids (LVA's) were measured by using the EROS solid-state system. The object and image distances of the LVA's were as in normal usage by a patient. The contrast thresholds of patients who use LVA's were also measured. All LVA's measured have more than adequate contrast transmission at the low frequencies that are important for these subjects, but many have wasted transmission at medium and high frequencies. LVA's with poorer high-frequency MTF can be used successfully by low-vision patients. It is suggested that in future design high resolution should be sacrificed for a greater lens diameter while maintaining a high MTF at low spatial frequencies.

关键词： modulation transfer functions LOW-VISION AIDS LOW VISION CONTRAST SENSITIVITY

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NUMERICAL-CALCULATION OF modulation transfer-functions FOR LOW-FREQUENCY MECHANICAL VIBRATIONS

NUMERICAL-CALCULATION OF MODULATION TRANSFER-FUNCTIONS FOR L...

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CONF ON AIRBORNE RECONNAISSANCE 14

作者： FISHER, M HADAR, O KOPEIKA, NS Ben-Gurion Univ. of the Negev (Israel)

ISBN: (纸本)0819404039

Numerical calculations of modulation transfer functions (MTFs) for low-frequency mechanical vibrations are presented. The problem is significant in practical reconnaissance where primary vibrations are at frequencies too low to be described by the usual closed form Bessel function MTF. The low vibration frequency situation involves random process blur radii and MTFs which can only be handled statistically since no closed form solution is possible. This is illustrated here. Comparisons are made to a closed form approximate MTF solution suggested previously. Agreement is generally good, especially for relatively large and linear blur radius situations.

关键词： modulation transfer functions Spatial frequencies Airborne reconnaissance Image quality Sensors Image resolution modulation Image processing Imaging systems Reconnaissance

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STREAK TUBE modulation transfer-functions 7

STREAK TUBE MODULATION TRANSFER-FUNCTIONS

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CONF ON ULTRAHIGH SPEED AND HIGH SPEED PHOTOGRAPHY, PHOTONICS, AND VIDEOGRAPHY 89

作者： WHITESON, A EG&G Energy Measurements (United States)

An exponential model is proposed for streak tube MTFs (modulation transfer functions) based on line spread function measurements. This model is used to derive performance characteristics such as temporal resolution, c... 详细信息

ISBN: (纸本)0819401919

关键词： modulation transfer functions Performance modeling Point spread functions High speed photography modulation Photography Contrast transfer function Fourier transforms Temporal resolution Imaging systems

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Edge-response functions, line-spread functions, and point-spread functions corresponding to electro-optical modulation transfer functions of the form exp-(f/fc)n

Edge-response functions, line-spread functions, and point-sp...

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Developments in Electronic Imaging Techniques II 1972

作者： Johnson, C.B. Bendix Research Laboratories SouthfieldMI United States

The modulation transfer functions (MTFs) of many optical and electro-optical imaging devices have the form (Ref. 1); T(f) = exp -(f/fc)n (1) where T(f) is the MTF, f is the spatial frequency in cycles/mm, fc is the frequency constant in cycles/mm, and n is the MTF index. It is usually possible to find values for the two MTF parameters fc and n such that the measured MTF agrees with equation (1) to within +0.05. Electro-optical devices have been classified (Ref. 2) in terms of the MTF parameters associated with each device. Now it is found that it is possible to extend this method of classification to optical devices and image transfer/display systems. In addition, the edge-response functions, line-spread functions, and point-spread functions associated with MTFs of this form are described, and the transformation equations are given.

关键词： modulation transfer functions Electro optics Optical components Image intensifiers Imaging devices Diffraction Atmospheric optics Silicon Electro optical imaging Spatial frequencies

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TEMPORAL-modulation transfer-functions IN PATIENTS WITH COCHLEAR IMPLANTS

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JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 1992年第4期91卷 2156-2164页

作者： SHANNON, RV House Ear Institute 2100 W. 3rd Street Los Angeles California 90057

Thresholds for the detection of amplitude modulation were measured in cochlear implant patients as a function of modulation frequency. Three types of threshold measures were taken: detection of amplitude modulation, detection of low-frequency sinusoidal current waveforms, and detection of beats in two-tone complexes. The temporal modulation transfer function (TMTF), defined as the plot of modulation detection thresholds as a function of modulation frequency, show low-pass filter characteristics with similar cutoff frequencies for all three tasks. The similarity of these three measures suggests a common temporal mechanism. While modulation detection differs somewhat in normal-hearing and implanted listeners, both exhibit the same general characteristics. The TMFTs are low pass with a cutoff frequency near 70 Hz for normal-hearing listeners and near 140 Hz for implanted listeners. Patients with cochlear implants can best detect temporal modulation at modulation frequencies below 300 Hz, and are most sensitive to 80- to 100-Hz modulation. At high carrier levels many implant patients could detect smaller modulation amplitudes than normal-hearing listeners, a finding that is consistent with the smaller intensity DLs for some implanted listeners at high levels. These results demonstrate that, while implant listeners cannot discriminate steady-state, high-frequency stimuli, speech information might be conveyed by the envelope of the high-frequency components of speech.

关键词： Cochlear implants modulation transfer functions Speech Time measurement Electric measurements

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TEMPORAL-modulation transfer-functions BASED UPON modulation THRESHOLDS

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JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 1979年第5期66卷 1364-1380页

作者： VIEMEISTER, NF Department of Psychology University of Minnesota Minneapolis Minnesota 55455

The detectability of amplitude modulation in the absence of spectral cues provides a quantitative description of temporal resolution for steady‐state signals with relatively small amplitude changes. modulation thresholds for sinusoidally amplitude‐modulated wideband noise were measured as a function of modulation frequency. The resulting ’’Temporal modulation transfer Function’’ (TMTF) shows a lowpass characteristic for modulation frequencies below about 800 Hz. The lowpass characteristic is extended up to approximately 2 kHz when the increment in average power produced by modulation is eliminated. The important parametric effects are summarized as follows: (1) TMTFs are independent of overall level, except at very low intensities; (2) the time constant indicated by the TMTF decreases as the center frequency of the band‐limited, modulated noise is increased; (3) modulation thresholds generally decrease with increasing duration of modulation, particularly at low modulation frequencies; (4) when the carrier is gated for the duration of modulation, the TMTF shows a highpass segment at low modulation frequencies. Although the TMTFs are not directly consistent with the attenuation characteristic of a simple lowpass filter, a model which incorporates such a filter, with a time constant of 2.5 ms, describes the entire TMTF and also describes the modulation functions obtained with square‐wave and pulse modulation. The wide bandwidth of initial filtering indicated by the model raises the important question of the role of peripheral filtering in determining the detectability of high‐frequency modulation.

关键词： Band models modulation transfer functions

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TEMPORAL modulation transfer-functions FOR AUDITION

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JOURNAL OF THE ACOUSTICAL SOCIETY OF AMERICA 1973年第1期53卷 312-+页

作者： VIEMEISTER, NF UNIV MINNESOTA MINNEAPOLIS MN 55455 USA

Systems analysis has been extensively used to study the spatial and temporal processing of visual inputs and recently has been applied to auditory filtering. Two techniques are discussed in the present paper, which extend this approach to auditory temporal processing. In the “modulation‐threshold” procedure, the threshold modulation amplitude of a sinusoidally modulated waveform (either sinusoids or noise) is determined. The function relating this threshold to modulation frequency is a temporal modulation transfer function (TMTF) and ideally is the attenuation characteristic of the temporal processing system. TMTFs obtained with this procedure show only low‐pass filtering and are 3 dB down at approximately 10 Hz. In the “temporal probe technique,” the threshold amplitude of a brief probe (either a bandpass filtered or a wide‐band pulse) is determined at several temporal locations in a noise masker whose amplitude is sinusoidally modulated. The function relating probe amplitude to its time of occurrence (the masking curve) can be well‐fitted by a sinusoid with a dc component. The amplitude spectrum (TMTF) and phase spectrum are determined from masking curves obtained at several modulation frequencies. The empirical TMTF indicates a shorter time constant and steeper attenuation rates than those obtained with the modulation‐threshold procedure. [This research was supported by the National Institutes of Health and by a Special Traineeship from NINDS.]

关键词： modulation transfer functions Wave attenuation Bandpass filters Noise propagation Spatial analysis

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An intercomparison of the modulation transfer functions of square and circular focal spots

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Medical Physics 1974年第4期1卷 204-209页

作者： Rao, Gopala U. V. Soong, An Liang Department of Radiology and Radiological Science The Johns Hopkins School of Medicine Baltimore Maryland 21205 United States

In field emission x ray tubes, the target is conical in shape and the projection of the focal spot along the central axis a circular disk. To determine the resolution capability of such tubes, a theoretical expression has been derived for the MTF of a circular focal spot. It has been shown that the MTF is given by the equation MTF = 2J1[Ïf0Î´(m â 1) / m] / [Ïf0Î´(m â 1) / m] where m is the magnification factor, f₀ the spatial frequency in the object plane, and Î´ the diameter of the focal spot. J₁ stands for the Bessel function of the first order. The above expression has been tested experimentally and used to compare circular focal spots with square focal spots. © 1972, The U. S. Secretary of Commerce on behalf of the United States. All rights reserved.

关键词： modulation transfer functions Field emission Tube theories

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A design study and advantages of meta-Alvarez lenses

A design study and advantages of meta-Alvarez lenses

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Photonic Instrumentation Engineering XII 2025

作者： Ding, Yijun Stone, Bryan D. Otake, Motoyuki Synopsys Incorporated 199 S. Los Robles Ave. Suite 400 PasadenaCA91101 United States

ISBN: (纸本)9781510684942

We study the aberrations of a meta-Alvarez lens introduced by an air gap between the two elements. We find that four aberrations change with the air gap thickness: Spherical, Tetrafoil, Coma, and Trefoil. These aberrations grow linearly with the air gap thickness;hence as the air gap increases, the image quality degrades. These results reveal an important benefit of using metalens for Alvarez systems: The flat profile of metalens enables minimal separation between the two lenses, hence potentially better imaging performance than refractive Alvarez lens. © 2025 SPIE.

关键词： Design Lenses Imaging systems Wavefronts Metalenses modulation transfer functions Code v Wavefront aberrations Aberration theory Optical aberrations Zernike polynomials

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Digital image acquisition and processing in medical x-ray imaging

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JOURNAL OF ELECTRONIC IMAGING 1999年第1期8卷 7-22页

作者： Aach, T Schiebel, U Spekowius, G Philips GmbH Res Labs D-52066 Aachen Germany

This contribution discusses a selection of today's techniques and future concepts for digital x-ray imaging in medicine. Advantages of digital imaging over conventional analog methods include the possibility to archive and transmit images in digital information systems as well as to digitally process pictures before display, for example, to enhance low contrast details. After reviewing two digital x-ray radiography systems for the capture of still x-ray images, we examine the real time acquisition of dynamic x-ray images (x-ray fluoroscopy). Here, particular attention is paid to the implications of introducing charge-coupled device cameras. We then present a new unified radiography/fluoroscopy solid-state detector concept. As digital image quality is predominantly determined by the relation of signal and noise, aspects of signal transfer, noise, and noise-related quality measures like detective quantum efficiency feature prominently in our discussions. Finally, we describe a digital image processing algorithm for the reduction of noise in images acquired with low x-ray dose. (C) 1999 SPIE and IS&T. [S1017-9909(99)00401-8].

关键词： Signal to noise ratio Interference (communication) X-rays Sensors X-ray imaging modulation transfer functions Fluoroscopy Spatial frequencies Electrons Image processing

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