Filter may refer to:

Chemistry, engineering and materials

In chemistry, engineering, or household usage, a device to separate mixtures. See:

• Filter (chemistry)
• Water filter
• Air filter
• Oil filter
• Pneumatic filter

Optics and photography

In optics and photography, a device to remove, or to enhance, certain ranges of wavelengths (colors) of light. See:

• filter (optics)
• photographic filter
• infrared filter
• H-alpha filter
• Chelsea filter

Signal processing

In signal-processing applications (such as telecommunications, music, and picture processing): a mathematical algorithm, or an electrical or mechanical device, to modify the contents of signals and to extract their salient features. See:

• electronic filter
• audio filter
• line filter
• digital filter
• Wiener filter
• Kalman filter

See filtering problem (stochastic processes) for the mathematical formalism.

Computing

In computing:

• filter (higher-order function)
• A program to process a data stream:
• filter (software)
• filter (Unix)
• mail filter
• Internet filter
• wordfilter
• DirectShow
• BPF filter expression used in the qualification of network data

Philosophy

• Category-based filtering of perception — according to (objectivist interpretations of) Kant
• interpretive filtering through concepts according to existentialism

Other

• In mathematics, a certain kind of subset of a partially ordered set. See
• filter (mathematics).
• In psychology, a type of learning blockage. See
• affective filter.
• In transportation, filtering forward, a practice that cyclists use to pass slow or stopped congested traffic.
• An aquarium filter.

Proper name

• Filter (band), an industrial rock band
• Filter (television), a show on the G4 channel:
• Filter (magazine), an off-beat indie music magazine
• Helicon Filter, a raster graphics editor

See also

• Filter coffee, a method for preparing coffee
• Filter feeder, an animal that strains food particles from water
• Philter, a magical potion
• Filtration
• Conversion