- 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. [ [http://www.nature.com/nrn/journal/v5/n8/box/nrn1476_BX2.html Box 2 : Visual objects in context : Nature Reviews Neuroscience ] ] In the general population of adults, the threshold for spatial frequency discrimination is about 7%. It is often poorer in dyslexic individuals [ [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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