- Spatial frequency
In

mathematics ,physics , andengineering ,**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. TheSI unit of spatial frequency is cycles permeter . Inimage processing applications, the spatial frequency often is measured as lines permillimeter , which is 1000 times smaller than the SI unit.In

wave mechanics , the spatial frequency $u$ is related to the wavelength $lambda$ by:$u\; =\; \{\; 1\; over\; lambda\; \}$

Likewise, the

wave number "k" is related to spatial frequency and wavelength by:$k\; =\; 2\; pi\; u\; =\; \{\; 2\; pi\; over\; lambda\; \}$

**Visual perception**In the study of

visual perception , sinusoidalgrating s are frequently used to probe the capabilities of the visual system. In these stimuli, spatial frequency is expressed as the number of cycles per degree ofvisual angle .

Different spatial frequencies convey different information about the appearance of a stimulus. High spatial frequencies represent abrupt spatial changes in the image. such as edges, and generally correspond to configural information and fine detail. Low spatial frequencies, on the other hand, represent global information about the shape, such as general orientation and proportions. [*[*] In the general population of adults, the threshold for spatial frequency discrimination is about 7%. It is often poorer in dyslexic individuals [*http://www.nature.com/nrn/journal/v5/n8/box/nrn1476_BX2.html Box 2 : Visual objects in context : Nature Reviews Neuroscience*]*[*] .*http://www.ncbi.nlm.nih.gov/pubmed/15031099?ordinalpos=4&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum Sequential spatial frequency discrimination is consistently impaired among adult dyslexics*]**References****ee also***

Fourier transform

*Fourier analysis

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