In
signal processing, a
filter is a device or process that removes from a
signal some unwanted component or feature. Filtering is a class of signal processing, the defining feature of filters being the complete or partial suppression of some aspect of the signal. Most often, this means removing some
frequencies and not others in order to suppress interfering signals and reduce background
noise. However, filters do not exclusively act in the
frequency domain; especially in the field of
image processing many other targets for filtering exist. Correlations can be removed for certain frequency components and not for others
without having to act in the frequency domain.