low-pass filter

Definition: Filter of optical or software type that lets through low-frequency data and blocks higher frequency data. * Optical type: softening filters used for portraiture are low-pass: they let through the low-frequency data of facial shape and main features, but block high-frequency data such as wrinkles and spots. * Software type: used to reduce noise by smoothing out differences in values of adjacent pixels e.g. by replacing the value of each pixel with the average of that pixel plus its neighbours. * Also known as spatial averager.

Related Terms: convolution, descreening

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