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 sinusoidal components (as determined by the Fourier transform) of the structure repeat per unit of distance. The SI unit of spatial frequency is cycles per meter. In image processing applications, spatial frequency is often expressed in units of cycles per millimeter and sometimes incorrectly in units of line pairs per millimeter (incorrect since a line pair may describe a square wave but not a sinusoidal wave).
In wave mechanics, the spatial frequency is commonly denoted by or sometimes, although the latter is also used to represent temporal frequency. It is related to the wavelength by the formula
Likewise, the wave number (e.g. in radians per meter) is related to spatial frequency and wavelength by
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Famous quotes containing the word frequency:
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—Jean Marzollo (20th century)