Filter - AbsoluteAstronomy.com

Chemistry, engineering and materials

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

Filter (aquarium)
Filter (aquarium)
Aquarium filters are critical components of both freshwater and marine aquaria. Aquarium filters remove physical and soluble chemical waste products from aquaria, simplifying maintenance...

, critical components of both freshwater and marine aquaria
Filter (chemistry)
Filter (chemistry)
In chemistry and common usage, a filter is a device that is designed to physically block certain objects or substances while letting others through. Filters are often used to remove solid substances suspended in fluids, for example to remove air pollution, to make water drinkable, and to prepare...

, a device (usually a membrane or layer) that is designed to physically block certain objects or substances while letting others through
Filter paper
Filter paper
Filter paper is a semi-permeable paper barrier placed perpendicular to a liquid or air flow. It is used to separate fine solids from liquids or air.-Properties:Filter paper comes in various porosities and grades depending on the applications it is meant for...

, 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
Air filter
A particulate air filter is a device composed of fibrous materials which removes solid particulates such as dust, pollen, mold, and bacteria from the air. A chemical air filter consists of an absorbent or catalyst for the removal of airborne molecular contaminants such as volatile organic compounds...

, 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
Pneumatic filter
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 pass through to a venturi, to a membrane that only allows air to pass through.-...

, 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)
Filter (optics)
Optical filters are devices which selectively transmit light of different wavelengths, usually implemented as plane glass or plastic devices in the optical path which are either dyed in the mass or have interference coatings....

, including types:
- Interference filter
  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...
- Dichroic filter
  Dichroic filter
  A dichroic filter, thin-film filter, or interference filter is a very accurate 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 characterized by the color of light that they...
Photographic filter
Photographic filter
In photography and videography, a filter is a camera accessory consisting of an optical filter that can be inserted in the optical path. The filter can be a square or oblong shape mounted in a holder accessory, or, more commonly, a glass or plastic disk with a metal or plastic ring frame, which...

, 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
H-alpha
H-alpha is a specific red visible spectral line created by hydrogen with a wavelength of 656.28 nm, which occurs when a hydrogen electron falls from its third to second lowest energy level...

, a specific red visible spectral line created by hydrogen with a wavelength of 6562.8 Å
Chelsea filter
Chelsea filter
In gemmology, a Chelsea filter is a dichromatic optical filter used for identifying coloured stones.-History:The "chelsea" filter was originally devised by Anderson and Payne in 1934 of the Gem testing Laboratory of the London Chamber of Commerce & Industry...
Astronomical filter
Astronomical filter
An astronomical filter is sometimes a telescope accessory used by amateur astronomers to simply enhance the details of celestial objects...

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

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

, especially,
- Electronic filter
  Electronic filter
  Electronic filters are electronic circuits which perform signal processing functions, specifically to remove unwanted frequency components from the signal, to enhance wanted ones, or both...
  
  , an electronic circuit which processes signals, for example to remove unwanted frequency components
- Digital filter
  Digital filter
  In electronics, computer science and mathematics, 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, the analog filter, which is...
  
  , 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
  Passive analogue filter development
  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 and later separation of multiple telephone conversations...

Computing

In computing:

Filter (higher-order function)
Filter (higher-order function)
In functional programming, filter is a higher-order function that processes a data structure 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.-Example:In Haskell, the code...

, 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)
  Filter (software)
  A filter is a computer program to process a data stream. Some operating systems such as Unix are rich with filter programs. Even Windows has some simple filters built into its command shell, most of which have significant enhancements relative to the similar filter commands that were available in...
  
  , a computer program to process a data stream
- Filter (Unix)
  Filter (Unix)
  In Unix and Unix-like operating systems, a filter is a program that gets most of its data from its standard input and writes its main results to its standard output . Unix filters are often used as elements of pipelines...
  
  , 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)
  Filter (video)
  A video filter is a software component that is used to decode audio and video. Multiple filters can be used in a filter chain, in which each filter receives input from its previous-in-line filter upstream, processes the input and outputs the processed video to its next-in-line filter downstream...
- Email filter
- Internet filter
- Wordfilter
  Wordfilter
  A wordfilter 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 words or phrases.The most primitive wordfilters search only for a specific string and replaces it...
  
  , 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
Berkeley Packet Filter
The Berkeley Packet Filter or BPF provides, on some Unix-like systems, a raw interface to data link layers, permitting raw link-layer packets to be sent and received...

filter expression used in the qualification of network data
DSL filter
DSL filter
A DSL filter is an analog low-pass filter installed between analog devices and a plain old telephone service telephone line, in order to prevent interference between such devices and a digital subscriber line service operating on the same line...

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

Philosophy

Category-based filtering
Category (Kant)
In Kant's philosophy, a category is a pure concept of the understanding. A Kantian category is a characteristic of the appearance of any object in general, before it has been experienced...

of perception — according to (objectivist interpretations of), Kant

Other

In mathematics, a certain kind of subset
Subset
In mathematics, especially in set theory, a set A is a subset of a set B if A is "contained" inside B. A and B may coincide. The relationship of one set being a subset of another is called inclusion or sometimes containment...

of a partially ordered set
Partially ordered set
In mathematics, especially order theory, a partially ordered set formalizes and generalizes the intuitive concept of an ordering, sequencing, or arrangement of the elements of a set. A poset consists of a set together with a binary relation that indicates that, for certain pairs of elements in the...

. See
- Filter (mathematics)
  Filter (mathematics)
  In mathematics, a filter is a special subset of a partially ordered set. A frequently used special case is the situation that the ordered set under consideration is just the power set of some set, ordered by set inclusion. Filters appear in order and lattice theory, but can also be found in...
  
  , a special subset of a partially ordered set
- Filtering problem (stochastic processes)
  Filtering problem (stochastic processes)
  In the theory of stochastic processes, the filtering problem is a mathematical model for a number of filtering problems in signal processing and the like. The general idea is to form some kind of "best estimate" for the true value of some system, given only some observations of that system...
  
  , 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)
Filter (band)
Filter is a rock group formed in 1993 in Cleveland by singer Richard Patrick and guitarist/programmer Brian Liesegang. Filter has released five studio albums, the most recent being The Trouble with Angels, which was released on August 17, 2010....

, an American rock band
Filter (TV series)
Filter (TV series)
Filter is an American television series on the G4 cable television channel which follows a countdown format. It was canceled in December 2005, resurrected in a re-formatted form, and then once again was canceled in August 2006. It is currently airing as a commercial break hosted by Candace Baily....

, a show on the G4 channel
Filter (magazine)
Filter (magazine)
FILTER, the publication that promises us that "Good music will prevail," is a seasonal American music and off-beat entertainment magazine. It features commentary and photos of up-and-coming musicians and filmmakers ranging from actors to writer-directors...

, an off-beat indie music magazine
Helicon Filter
Helicon Filter
Helicon Filter, also referred to as Helicon, Filter, or as HF, is a proprietary commercial and shareware photo editing software program for Microsoft Windows, similar to such programs as Adobe Photoshop and GIMP, developed and published by Helicon Soft Ltd...

, a raster graphics editor
Filter (theatre company)