spatial frequency


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frequency, spatial

The rate of alternation of the luminance in a visual stimulus as a function of length, usually expressed in cycles per degree. See cycle per degree; Fourier analysis; contrast sensitivity function.
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann
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Data are reported as means [+ or -] SE for each spatial frequency (A: 0.5, 1.25, 2.5, 4, 10, and 20 cpd) and for each angular frequency stimuli (B: 1,2,4, 24, 48, and 96 cycles/360[degrees]) for n = 20 in each group.
The spatial frequency is proportional to the square root of the shear modulus and inversely proportional to the square root of the film thickness and the apparent surface stress in contrast to the surface modulation of an elastic half space.
Although it was not possible with the present equipment, it would be interesting to measure individuals on the task using even larger letter sizes in order to engage other channels at the lower end of the spatial frequency range.
The mean logarithmic values of FACT scores measured in each spatial frequency of the insulin resistant group and control group were in normal range (1.51[+ or -]0.19 vs 1.45[+ or -]0.16, p=0.2 at 1.5 cpd; 1.67[+ or -]0.25 vs 1.62[+ or -]0.20, p=0.4 at 3 cpd; 1.66[+ or -]0.26 vs 1.63[+ or -]0.18, p=0.5 at 6 cpd; 1.32[+ or -]0.25 vs 1.25[+ or -]0.16, p=0.2 at 12 cpd; and 0.95[+ or -]0.33 vs 0.82[+ or -]0.29, p=0.1 at 18 cpd).
Conventional letters particularly vary in their low spatial frequency content (the energy near the centre of the spectrum in Figure 4) so that two letters that are very different in their low spatial frequency information such as the letters 'A' and 'U', can remain distinguishable from one another for far longer than two letters that are more similar in their low spatial frequency information but differ in their high-frequency information, for example, the letters 'O' and 'Q'.
In this paper, a new Gabor histogram is constructed by including the spatial frequency domain information and spatial location information, and the entropic thresholding method based on Gabor histogram is proposed, which can effectively distinguish foreground/background, edge and noise of image.
This method is based on calculating the probability of the participant making consecutive hits, that is, in approximately 100 presentations with two stimuli to choose from (test stimulus and neutral stimulus), the spatial frequency (test stimulus) is perceived by the participant approximately 79% of the time.
where [f.sub.1] and [f.sub.2] represent, respectively, the lower and upper limits of the chosen spatial frequency range.
When considering the walk-off effect, the sidelobes of the pump spectrum caused by its intensity modulation are not met the phase-matching condition, and these spatial frequency components are accordingly suppressed during the OPA process.
Therefore, automatic pairing of the estimated spatial frequency p and Doppler frequency V can be realized by decomposition of complex matrix [[PHI].sub.[mu]] + j[[PHI].sub.v], that is,
For each given value of n there is a specific spatial frequency component [f.sub.s] = n[DELTA], and there are N - 1 terms.
Objective evaluation of quality is made in terms of 7 indexes, such as the information entropy (IE), spatial frequency (SF), mean gradient (AG) [14], clarity (MC), mutual information (MI), standard deviation (SD) [15], and edge information delivery factor ([Q.sup.AB/F] high weight evaluation index) [16-19].

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