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...
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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.
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 ...
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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.
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...
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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...
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ISBN:
(纸本)0819401919
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, channel width and pixel size. These results are compared with those predicted by a Gaussian model for the MTF.
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 fr...
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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.
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, d...
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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 modulationtransfer 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.
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 thresh...
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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 modulationtransfer 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 modulationfunctions 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.
Photon counting CT (PCCT) uses energy-resolving detectors to count and assign individual incident x-ray photons to preset energy bins, offering improved image quality, energy discrimination capability, and dose effici...
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Sightful is a leading innovator in extended reality (XR) productivity solutions, founded in 2020. Our software integrates with current market hardware to enhance workplace efficiency and user experience. Since our inc...
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We present metrology methodologies for projectors used in AR glasses, focusing on image quality, pupil quality, and boresight measurements. Accurate metrology is critical for AR technology, requiring different approac...
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