Spatial frequency

Spatial frequency is the number of repeating cycles of a pattern per unit distance. It describes how finely spaced a pattern’s variations are, often in cycles per degree or cycles per millimeter.

Sinusoidal grating: A repeating pattern whose intensity varies smoothly as a sine wave across space. Its spacing and orientation provide a standard way to specify spatial frequency.
Contrast sensitivity function: A function describing sensitivity to contrast across spatial frequencies. It shows which pattern scales the visual system detects most readily.
Wavelength: The distance between corresponding points in successive cycles of a wave. For a regular pattern, spatial frequency is the inverse of its wavelength.
Spatial period: The distance required for a spatial pattern to complete one full cycle. It measures cycle length rather than cycles per unit distance.
Fourier transform: A mathematical operation that represents a signal as a combination of frequencies and phases. It decomposes an image into spatial frequencies and their orientations.
Visual acuity: The ability to resolve fine visual detail, commonly measured with standardized visual targets. High-frequency patterns probe the finest detail that vision can distinguish.
Temporal frequency: The number of repeating cycles of a signal per unit time. It counts changes over time, whereas spatial frequency counts repetitions across distance.
Spatial wavelength: The distance between corresponding points in successive cycles of a spatial pattern. It is another name for the inverse of spatial frequency in periodic patterns.
Fourier series: A representation of a periodic function as a sum of sinusoidal components. It explains how complex repeating patterns contain multiple spatial frequencies.
Modulation transfer function: A measure of how an imaging system transfers contrast at different spatial frequencies. It reveals how lenses, sensors, and displays blur fine patterns.

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