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antialiasing filter (AAF)

Aliasing is interference-induced noise that occurs primarily at high frequencies. Aliasing can show up in electrical signals and optically captured images and can manifest itself in different types of interference and distortion. To avoid aliasing, there are different approaches to antialiasing.

Antialiasing filter for electrical signals

For electrical signals, antialiasing is performed by antialiasing filters(AAF). These are low-pass filters that are connected upstream of the A/D converter or the electronic signal processing and reduce the bandwidth to such an extent that their frequencies comply with the sampling theorem. Higher input frequencies cannot pass through the AAF filter and therefore cannot cause aliasing. This allows the sampled signal to be interpreted unambiguously.

Characteristics of the antialiasing filter

Characteristics of the antialiasing filter

Antialiasing filter in digital photography

In image sensors, the antialiasing filter is an optical low-pass filter (OLPF) that acts as a soft focus and is located in front of the optics. The effect of aliasing is due to the pixel pitch. If captured image motifs are similarly finely structured as the pixel raster, then moirés or rainbow-colored structures occur. These interference effects are due to the fact that it is no longer possible to interpolate between the different pixels. These effects are avoided by antialiasing filters, which make the captured image slightly blurred.

Antialiasing filters for digital and video cameras, photo:

Antialiasing filters for digital and video cameras, photo:

Optical antialiasing filters consist of several different crystal layers such as lithium niobate that refract light into multiple beams, polarize and refract it, direct it to different pixels on the image sensor, and activate them. The wavelengths transmitted by the optical antialiasing filter can be changed by altering the spacing between the crystal layers.

Englisch: antialiasing filter - AAF
Updated at: 16.12.2021
#Words: 274
Links: interference (I), noise (N), distortion, aliasing, upstream
Translations: DE

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