 FACTOID # 21: 15% of Army recruits from South Dakota are Native American, which is roughly the same percentage for female Army recruits in the state.

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Encyclopedia > Spatial frequency

In mathematics, physics, and engineering, spatial frequency is a characteristic of any structure that is periodic across position in space. The spatial frequency is a measure of how often the structure repeats per unit of distance. The SI unit of spatial frequency is cycles per meter. In image processing applications, the spatial frequency often is measured as lines per millimeter, which is 1000 times smaller than the SI unit. Wikibooks Wikiversity has more about this subject: School of Mathematics Wikiquote has a collection of quotations related to: Mathematics Look up Mathematics in Wiktionary, the free dictionary Wikimedia Commons has media related to: Mathematics Inter. ... Since antiquity, people have tried to understand the behavior of matter: why unsupported objects drop to the ground, why different materials have different properties, and so forth. ... Engineering applies scientific and technical knowledge to solve human problems. ... The International System of Units (abbreviated SI from the French language name SystÃ¨me International dUnitÃ©s) is the most widely used system of units. ... Cycles are series of states or conditions that repeat themselves, usually after a regular or nearly regular period. ... The metre, or meter (symbol: m) is the SI base unit of length. ... This article needs to be cleaned up to conform to a higher standard of quality. ... A millimetre (American spelling: millimeter), symbol mm is an SI unit of length that is equal to one thousandth of a metre. ...

In wave mechanics, the spatial frequency $nu$ is related to the wavelength $lambda$ by The wave equation is an important partial differential equation which generally describes all kinds of waves, such as sound waves, light waves and water waves. ... $nu = { 1 over lambda }$

Likewise, the wave number k is related to spatial frequency and wavelength by Wavenumber in most physical sciences is a wave property inversely related to wavelength, having units of inverse length. ... $k = 2 pi nu = { 2 pi over lambda }$ Results from FactBites:

 Nikon MicroscopyU: Modulation Transfer Function (4055 words) As the spatial frequency approaches very large values, the square wave response resembles that of a sinusoid, yielding graphs of the contrast transfer function and the modulation transfer function that are virtually identical. At low spatial frequencies, image contrast is the highest, but falls to zero as the spatial frequency is increased beyond a certain point (drawn in Figure 2 as a reduction in amplitude produced in the image). It is composed of sinusoidal patterns having a spatial frequency range between 0.2 and 80 line pairs per millimeter with a grayscale optical density range varying between 0.2 and 1.2 and an 80 percent modulation of the sine waves.
 Spatial Frequency (4828 words) The unit employed to express spatial frequency is the number of cycles that fall within one degree of visual angle (each cycle is one dark and one light bar). However, at intermediate spatial frequencies, the contrast in the image is degraded by the butter on the lens. If those objects contain only very low spatial frequencies (very large objects) or only very high spatial frequencies (very small objects or fine details), they will be less visible and their contrast will have to be high in order for those objects to be seen.
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