Spatial frequency

The spatial frequency ( the spatial frequency and, symbols, or R k ) is the reciprocal of the spatial period length.

Physics

In general, the notion of a time-periodic change in size is associated with the term period. However, the term of the period can easily be expanded to arbitrary periodic functions, as well as to spatially varying sizes.

Is the considered physical size of about one-dimensional position -dependent, so the period length has the dimension of length and is in the international system of units in meters ( m) specified. Accordingly, the number of periods per unit length of the spatial frequency indicates, that has the dimension 1/length. Thus, for the spatial frequency of electromagnetic waves, the wave number in cycles per centimeter in use and for frequency broom (Fig.), the unit of line pairs per millimeter ( lp / mm).

The characterization of a locally varying function after minority with determining spatial frequencies is not as graphic as the decomposition of a sound in fundamental and harmonic tones, yet it provides the basis for the Fourier optics and image compression algorithms such as JPEG.

Psychology

In the psychology of perception of vision called " spatial frequency " is the number of edges (see edge detection ) per degree of visual angle. Images with low spatial frequency are blurred and flat images with high spatial frequency are rich in detail and with easily recognizable outlines. In the visual cortex, there are neurons that are specialized to analyze the spatial frequency of an image. The perceived contrast is here by the contrast sensitivity function (English: Contrast Sensitivity Function ( CSF) ) specified. Is recognized Optimal rasterization of about 9 pairs of lines (ie switching between lighter and darker lines) per degree of visual angle. At four times that amount of spatial frequency, ie, at about 36 line pairs per degree, the contrast is perceived by the people, only about 10 percent.