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What is a filter


product-30-0a-bd-2c9dc0d43d2ecac4281372906dChemistry, engineering and materials

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 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.


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


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


In mathematics. 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
Lane splitting, a practice that cyclists use to pass slow or stopped congested traffic

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