Filter, filtering or filters may refer to:

Science and technology

Computing

Filter (higher-order function) In functional programming, filter is a higher-order function that processes a data structure (usually a list) in some order to produce a new data structure containing exactly those elements of the original data structure for which a given predicat ...

, in functional programming *

Filter (software) A filter is a computer program or subroutine to process a stream, producing another stream. While a single filter can be used individually, they are frequently strung together to form a pipeline. Some operating systems such as Unix are rich with f ...

, a computer program to process a data stream * Filter (video), a software component that performs some operation on a multimedia stream *

Email filtering Email filtering is the processing of email to organize it according to specified criteria. The term can apply to the intervention of human intelligence, but most often refers to the automatic processing of messages at an SMTP server, possibly appl ...

, the processing of email to organize it according to specified criteria *

Content-control software An Internet filter is software that restricts or controls the content an Internet user is capable to access, especially when utilized to restrict material delivered over the Internet via the Web, Email, or other means. Content-control software det ...

also known as an Internet filter *

Wordfilter A wordfilter (sometimes referred to as just "filter" or "censor") is 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 w ...

, a script typically used on Internet forums or chat rooms *

Berkeley Packet Filter The Berkeley Packet Filter (BPF) is a technology used in certain computer operating systems for programs that need to, among other things, analyze network traffic. It provides a raw interface to data link layers, permitting raw link-layer packets ...

, filter expression used in the qualification of network data *

DSL filter A DSL filter (also DSL splitter or microfilter) is an analog low-pass filter installed between analog devices (such as telephones or analog modems) and a plain old telephone service (POTS) line. The DSL filter prevents interference between su ...

, a low-pass filter installed between analog devices and a telephone line *

Helicon Filter Helicon Filter, also referred to as Helicon, Filter, or as HF, was a proprietary commercial and shareware photo editing software program for Microsoft Windows, similar to such programs as Adobe Photoshop and GIMP, developed and published ...

, a raster graphics editor * Filter (large eddy simulation), a mathematical operation intended to remove a range of small scales from the solution to the Navier-Stokes equations *

Kalman filter For statistics and control theory, Kalman filtering, also known as linear quadratic estimation (LQE), is an algorithm that uses a series of measurements observed over time, including statistical noise and other inaccuracies, and produces estimat ...

, an approximating algorithm in optimal control applications and problems

Device

Filter (chemistry) Filtration is a physical separation process that separates solid matter and fluid from a mixture using a ''filter medium'' that has a complex structure through which only the fluid can pass. Solid particles that cannot pass through the filter ...

, a device which separates solids from fluids (liquids or gases) by adding a medium through which only the fluid can pass **

Filter (aquarium) Aquarium filters are critical components of both freshwater and marine aquaria.Leibel WS (1993) ''A fishkeepers guide to South American cichlids.'' Tetra Press. Belgium pg 12-14. Aquarium filters remove physical and soluble chemical waste products ...

, critical components of both freshwater and marine aquaria **

Filter paper Filter paper is a semi-permeable paper barrier placed perpendicular to a liquid or air flow. It is used to separate fine solid particles from liquids or gases. The raw materials are different paper pulps. The pulp may be made from softwood, hardwo ...

, 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 particulate air filter is a device composed of fibrous, or porous materials which removes solid particulates such as dust, pollen, mold, and bacteria from the air. Filters containing an adsorbent or catalyst such as charcoal (carbon) may als ...

, a device composed of fibrous materials which removes solid particulates such as dust, pollen, mold, and bacteria from the air **

Oil filter An oil filter is a filter designed to remove contaminants from engine oil, transmission oil, lubricating oil, or hydraulic oil. Their chief use is in internal-combustion engines for motor vehicles (both on- and off-road ), powered aircraft, r ...

, a filter to remove contaminants from engine oil, transmission oil, lubricating oil, or hydraulic oil **

Pneumatic filter {{Unreferenced, date=March 2008 A pneumatic filter is a device which removes contaminants from a compressed air stream. This can be done using a number of different techniques, from using a "media" type that traps particulates, but allows air to p ...

, a device which removes contaminants from a compressed air stream **

Water filter A water filter removes impurities by lowering contamination of water using a fine physical barrier, a chemical process, or a biological process. Filters cleanse water to different extents, for purposes such as: providing agricultural irrigation ...

, removes impurities from water by means of a fine physical barrier, a chemical process or a biological process **

Cigarette filter A cigarette filter, also known as a filter tip, is a component of a cigarette, along with cigarette paper, capsules and adhesives. Filters were introduced in the early 1950s. Filters may be made from plastic cellulose acetate fiber, paper or ...

, a part of a cigarette intended to filter the smoke inhaled by a smoker **

Coffee filter A coffee filter is a filter used for brewing coffee. Filters made of paper (disposable), or cloth, plastic, and metal (reusable) are used. The filter allows the liquid coffee to flow through, but traps the coffee grounds. Paper filters remove o ...

, a utensil used to separate coffee grounds from liquid coffee **

Fuel filter A fuel filter is a filter used to screens out foreign particles or liquids from the fuel. Most internal combustion engines use a fuel filter, in order to protect the components in the fuel system. Filters for foreign particles Unfiltered fuel ...

, found in most internal combustion engines **

Filtration (wine) In winemaking, clarification and stabilization are the processes by which insoluble matter suspended in the wine is removed before bottling. This matter may include dead yeast cells ( lees), bacteria, tartrates, proteins, pectins, various tannin ...

Sieve A sieve, fine mesh strainer, or sift, is a device for separating wanted elements from unwanted material or for controlling the particle size distribution of a sample, using a screen such as a woven mesh or net or perforated sheet material. T ...

or macroscopic filter, a device for separating wanted elements from unwanted material

Mathematics

Filter (mathematics) In mathematics, a filter or order filter is a special subset of a partially ordered set (poset). Filters appear in order and lattice theory, but can also be found in topology, from which they originate. The dual notion of a filter is an ord ...

, a special subset of a partially ordered set. *

Filter (set theory) In mathematics, a filter on a set X is a family \mathcal of subsets such that: # X \in \mathcal and \emptyset \notin \mathcal # if A\in \mathcal and B \in \mathcal, then A\cap B\in \mathcal # If A,B\subset X,A\in \mathcal, and A\subset B, then ...

, a special family of subsets that forms an (order theoretic) filter with respect to set inclusion *

Filters in topology Filters in topology, a subfield of mathematics, can be used to study topological spaces and define all basic topological notions such a convergence, continuity, compactness, and more. Filters, which are special families of subsets of some give ...

, the use of collections of subsets to describe convergence. *

Filtering problem (stochastic processes) In the theory of stochastic processes, filtering describes the problem of determining the state of a system from an incomplete and potentially noisy set of observations. While originally motivated by problems in engineering, filtering found applic ...

, a mathematical model for a number of filtering problems in signal processing and the like. *

Filtration (mathematics) In mathematics, a filtration \mathcal is an indexed family (S_i)_ of subobjects of a given algebraic structure S, with the index i running over some totally ordered index set I, subject to the condition that ::if i\leq j in I, then S_i\subseteq ...

, an indexed set of subobjects of a given algebraic structure S.

Optics

Optical filter An optical filter is a device that selectively transmits light of different wavelengths, usually implemented as a glass plane or plastic device in the optical path, which are either dyed in the bulk or have interference coatings. The optical p ...

, selectively transmits light of different wavelengths **

Interference filter An interference filter or dichroic filter is an optical filter that reflects one or more spectral bands or lines and transmits others, while maintaining a nearly zero coefficient of absorption for all wavelengths of interest. An interference filte ...

, reflects one or more spectral bands or lines and transmits others, while maintaining a nearly zero coefficient of absorption for all wavelengths of interest **

Dichroic filter A dichroic filter, thin-film filter, or interference filter is a color filter used to selectively pass light of a small range of colors while reflecting other colors. By comparison, dichroic mirrors and dichroic reflectors tend to be characteri ...

, a very accurate color filter used to selectively pass light of a small range of colors while reflecting other colors **

Hydrogen-alpha filter H-alpha (Hα) is a specific deep-red visible spectral line in the Balmer series with a wavelength of 656.28 nm in air and 656.46 nm in vacuum; it occurs when a hydrogen electron falls from its third to second lowest energy level. H-alpha ...

, an optical filter that transmits a narrow bandwidth of light centred on the H-alpha wavelength **

Photographic filter In photography and cinematography, a filter is a camera accessory consisting of an optical filter that can be inserted into the optical path. The filter can be of a square or oblong shape and mounted in a holder accessory, or, more commonly, a ...

, 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 ** Chelsea filter, a dichromatic optical filter used for identifying coloured stones **

Astronomical filter An astronomical filter is a telescope accessory consisting of an optical filter used by amateur astronomers to simply improve the details and contrast of celestial objects, either for viewing or for photography. Research astronomers, on the othe ...

, a telescope accessory used to enhance the details of celestial objects

Signal processing

Filter (signal processing) In signal processing, a filter is a device or process that removes some unwanted components or features from a signal. Filtering is a class of signal processing, the defining feature of filters being the complete or partial suppression of some aspe ...

Electronic filter Electronic filters are a type of signal processing filter in the form of electrical circuits. This article covers those filters consisting of lumped electronic components, as opposed to distributed-element filters. That is, using components ...

, an electronic circuit which processes signals, for example to remove unwanted frequency components **

Digital filter In signal processing, a digital filter is a system that performs mathematical operations on a sampled, discrete-time signal to reduce or enhance certain aspects of that signal. This is in contrast to the other major type of electronic filter, t ...

, a system that performs mathematical operations to reduce or enhance certain aspects of a signal **

Analogue filter Analogue filters are a basic building block of signal processing much used in electronics. Amongst their many applications are the separation of an audio signal before application to bass, mid-range, and tweeter loudspeakers; the combining ...

, a basic building block of signal processing much used in electronics ** Filters used in

digital image processing Digital image processing is the use of a digital computer to process digital images through an algorithm. As a subcategory or field of digital signal processing, digital image processing has many advantages over analog image processing. It allo ...

Arts and entertainment

* ''Filter'' (TV series), a show on the G4 channel * ''Filter'' (magazine), an off-beat indie music magazine * Filter Theatre, a British theatre company *

The Filter The Filter's TV personalisation products increase viewing, loyalty and revenue. Their data science underpins the business decisions of the world’s most forward thinking broadcasters. Founded in 2004, it has ties to musician Peter Gabriel an ...

, a digital content services company based in England *

Filter (band) Filter is an American rock music, rock band formed in 1993 in Cleveland, Ohio, by singer Richard Patrick and guitarist and programmer Brian Liesegang. The band was formed when Patrick desired to start his own band after leaving Nine Inch Nails a ...

, an American rock band * "Filter", a song from the album '' Bend'' by 8stops7 * "Filter", a song from the album '' Map of the Soul: 7'' by BTS

Social media

Filter (social media) Filters are appearance-altering digital image effects often used on social media. They initially simulated the effects of camera filters, and they have since developed with facial recognition technology and computer-generated augmented reality. ...

, an appearance-altering digital image effect for social media *

Beauty filter A beauty filter is a filter applied to still photographs, or to video in real time, to enhance the physical attractiveness of the subject. Typical effects of such filters include smoothing skin texture and modifying the proportions of facial fea ...

, a social media effect specifically meant to increase physical attractiveness

Other uses

Category Category, plural categories, may refer to: Philosophy and general uses * Categorization, categories in cognitive science, information science and generally *Category of being * ''Categories'' (Aristotle) *Category (Kant) *Categories (Peirce) * ...

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

Affective filter The input hypothesis, also known as the monitor model, is a group of five hypotheses of second-language acquisition developed by the linguist Stephen Krashen in the 1970s and 1980s. Krashen originally formulated the input hypothesis as just one ...

, an impediment to learning or acquisition caused by negative emotional ("affective") responses to one's environment *

Lane splitting Lane splitting is riding a bicycle or motorcycle between lanes or rows of slow moving or stopped traffic moving in the same direction. It is sometimes called whitelining, or stripe-riding. This allows riders to save time, bypassing traffic cong ...

, a practice that cyclists use to pass slow or stopped congested traffic *The ability of a person to self- censor themselves (their thoughts) whilst speaking