Filter

Filter may refer to:

Chemistry, engineering and materials

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

• Filter (aquarium), critical components of both freshwater and marine aquaria
• Filter (chemistry), a device (usually a membrane or layer) that is designed to physically block certain objects or substances while letting others through
• Filter paper, a semi-permeable paper barrier placed perpendicular to a liquid or air flow. It is used to separate fine solids from liquids or air
• Air filter, a device composed of fibrous materials which removes solid particulates such as dust, pollen, mold, and bacteria from the air
• Oil filter, a filter to remove contaminants from engine oil, transmission oil, lubricating oil, or hydraulic oil
• Pneumatic filter, a device which removes contaminants from a compressed air stream
• Water filter, removes impurities from water by means of a fine physical barrier, a chemical process or a biological process. Filters cleanse water to various extents for irrigation, drinking water, aquariums, and swimming pools

Optics and photography

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

• Filter (optics), including types:
  • Interference filter
  • Dichroic filter
• Photographic filter, a camera accessory consisting of an optical filter that can be inserted in the optical path
• Infrared cut-off filter, designed to reflect or block mid-infrared wavelengths while passing visible light
• H-alpha filter, a specific red visible spectral line created by hydrogen with a wavelength of 6562.8 Å
• Chelsea filter
• Astronomical filter, a telescope accessory used to enhance the details of celestial objects.

Turbulence modeling

In turbulence modeling, a procedure to dampen or remove the highest frequencies of the flow:

• Filter (large eddy simulation), in the context of large eddy simulation (LES) is a mathematical operation intended to remove a range of small scales from the solution to the Navier-Stokes equations

Signal processing

In signal processing, especially electronics, an algorithm or device for removing part(s) of a signal:

• Filter (signal processing), especially,
  • Electronic filter, an electronic circuit which processes signals, for example to remove unwanted frequency components
  • Digital filter, a system that performs mathematical operations to reduce or enhance certain aspects of a signal
  • Analogue filter, a basic building block of signal processing much used in electronics, see Passive analogue filter development

Computing

In computing:

• Filter (higher-order function), a higher-order function that processes a data structure (typically a list) in some order to produce a new data structure containing exactly those elements of the original data structure for which a given predicate returns the boolean value true
• A program to process a data stream:
  • Filter (software), a computer program to process a data stream
  • Filter (Unix), a program that gets most of its data from its standard input (the main input stream) and writes its main results to its standard output (the main output stream)
  • Filter (video)
  • Email filter
  • Internet filter
  • Wordfilter, a script typically used on Internet forums or chat rooms that automatically scans users' posts or comments as they are submitted and automatically changes or censors particular words or phrases
• BPF filter expression used in the qualification of network data
• DSL filter, a low-pass filter installed between analog devices and a telephone line

Philosophy

• Category-based filtering of perception — according to (objectivist interpretations of), Kant

Other

• In mathematics, a certain kind of subset of a partially ordered set. See
  • Filter (mathematics), a special subset of a partially ordered set
  • Filtering problem (stochastic processes), a mathematical model for a number of filtering problems in signal processing and the like
• In psychology, a type of learning blockage. See
  • Affective filter, an impediment to learning or acquisition caused by negative emotional ("affective") responses to one's environment. It is a hypothesis of second language acquisition theory, and a field of interest in educational psychology
• In transportation. See
  • Filtering forward, a practice that cyclists use to pass slow or stopped congested traffic

Proper name

• Filter (band), an American rock band
• Filter (TV series), a show on the G4 channel
• Filter (magazine), an off-beat indie music magazine
• Helicon Filter, a raster graphics editor
• Filter (theatre company)

See also

• Filter coffee, a method for preparing coffee
• Filter feeder, an animal that strains food particles from water
• Philter, a magical potion
• Filtration, a mechanical or physical operation which is used for the separation of solids from fluids (liquids or gases) by interposing a medium through which only the fluid can pass
• Cigarette filter, a part of a cigarette intended to filter the smoke inhaled by a smoker