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=== False color === [[Image:Lasvegas.terra.1500pix.jpg|thumb|A traditional false-color satellite image of Las Vegas. Grass-covered land (e.g. a golf course) appears in red.]] In contrast to a true-color image, a '''false-color image''' sacrifices natural color rendition in order to ease the [[feature detection (computer vision)|detection of features]] that are not readily discernible otherwise – for example the use of near infrared for the detection of vegetation in satellite images.<ref name="autogenerated1"/> While a false-color image can be created using solely the visual spectrum (e.g. to accentuate color differences), typically some or all data used is from [[electromagnetic radiation]] (EM) outside the [[visual spectrum]] (e.g. [[infrared]], [[ultraviolet]] or [[X-ray]]). The choice of spectral bands is governed by the physical properties of the object under investigation. As the human eye uses three spectral bands (see [[trichromacy]] for details), three spectral bands are commonly combined into a false-color image. At least two spectral bands are needed for a false-color encoding,<ref name="Mars Art Gallery Articles">{{cite web|url=http://www.marsartgallery.com/color.html |title=Mars Art Gallery Articles |publisher=www.marsartgallery.com |access-date=2012-09-01}}</ref> and it is possible to combine more bands into the three visual RGB bands – with the eye's ability to discern three channels being the limiting factor.<ref>{{cite web |url=http://www.nasaimages.org/luna/servlet/detail/nasaNAS~12~12~64086~168431:NGC-3627--M66- |archive-url=https://web.archive.org/web/20110901014618/http://www.nasaimages.org/luna/servlet/detail/nasaNAS~12~12~64086~168431%3ANGC-3627--M66- |archive-date=2011-09-01 |title=NGC 3627 (M66) - NASA Spitzer Space Telescope Collection |publisher=www.nasaimages.org |date=2005-09-15 |access-date=2012-09-01 |url-status=dead }}</ref> In contrast, a "color" image made from one spectral band, or an image made from data consisting of non-EM data (e.g. elevation, temperature, tissue type) is a ''pseudocolor image'' (see below). For true color, the [[RGB]] channels (red "R", green "G" and blue "B") from the camera are mapped to the corresponding RGB channels of the image, yielding a "RGB→RGB" mapping. For false color this relationship is changed. The simplest false-color encoding is to take an RGB image in the visible spectrum, but map it differently, e.g. "GBR→RGB". For traditional false-color satellite images of [[Earth]] a "NRG→RGB" mapping is used, with "N" being the near-infrared spectral band (and the blue spectral band being unused) – this yields the typical "vegetation in red" false-color images.<ref name="autogenerated1"/><ref>{{cite web |author=GDSC, {{lang|nl|Nationaal Lucht- en Ruimtevaartlaboratorium}} (National Laboratory of Air and Space Transport), Netherlands |publisher={{abbr|GDSC|Geospatial Data Service Centre}}, {{lang|nl|Nationaal Lucht- en Ruimtevaartlaboratorium}} (National Laboratory of Air and Space Transport), Netherlands |title=Band combinations |url=http://gdsc.nlr.nl/gdsc/en/information/earth_observation/band_combinations |url-status=dead |archive-url=https://web.archive.org/web/20120817005009/http://gdsc.nlr.nl/gdsc/en/information/earth_observation/band_combinations |archive-date=2012-08-17 }}</ref> False color is used (among others) for satellite and space images: Examples are [[remote sensing]] satellites (e.g. [[Landsat]], see example above), [[space telescope]]s (e.g. the [[Hubble Space Telescope]]) or [[space probe]]s (e.g. ''[[Cassini-Huygens]]''). Some spacecraft, with [[Rover (space exploration)|rovers]] (e.g. the [[Mars Science Laboratory]] ''Curiosity'') being the most prominent examples, have the ability to capture approximate true-color images as well.<ref name="universetoday1"/> [[Weather satellite]]s produce, in contrast to the spacecraft mentioned previously, grayscale images from the visible or infrared spectrum. {{multiple image | align = center <!-- Header -->| header = Examples for the application of false color: <!-- Image 1 -->| width1 = 327 | image1 = Daedelus comparison, remote sensing in precision farming (rotated).jpg | caption1 = These three false-color images demonstrate the application of remote sensing in [[precision agriculture]]: The left image shows vegetation density and the middle image presence of water (greens / blue for wet soil and red for dry soil). The right image shows where crops are under [[Plant stress measurement|stress]], as is particularly the case in fields 120 and 119 (indicated by red and yellow pixels). These fields were due to be irrigated the following day. <!-- Image 2 -->| width2 = 200 | image2 = Sig05-016.jpg | caption2 = This false-color composite image of the spiral galaxy [[Messier 66]] is combining four infrared spectral bands from 3.6 to 8.0 [[micrometers]]. The contribution from starlight (measured at 3.6 micrometers) has been subtracted from the 5.8 and 8 micrometer band to enhance the visibility of the [[polycyclic aromatic hydrocarbon]] emissions. <!-- Image 3 -->| width3 = 200 | image3 = Eagle_Nebula_-_GPN-2000-000987.jpg | caption3 = This iconic picture of the [[Eagle Nebula]] is false-color, as can be inferred from the pink stars. Three pictures were taken by the [[Hubble Space Telescope]], the first picking up light in the frequency of sulfur ions (arbitrarily assigned to the color red), the second hydrogen (green), and the third oxygen ions (blue). The actual color of the nebula is unknown, but if one viewed it at a distance making the 1-light-year-long "pillars" similarly visible, is probably a nearly uniform brownish grey to human eyes. }} False color has a range of scientific applications. Spacecraft often employ false-color methods to help understand the composition of structures in the universe such as nebula and galaxies.<ref>{{Cite web |title=The Truth About Hubble, JWST, and False Color |url=https://asd.gsfc.nasa.gov/blueshift/index.php/2016/09/13/hubble-false-color/ |access-date=2022-03-09 |website=NASA Blueshift |language=en-US}}</ref> The frequency of light emitted by different ions in space are assigned contrasting colors, allowing the chemical composition of complex structures to be better separated and visualised. The image of the Eagle Nebula above is a typical example of this; the Hydrogen and Oxygen ions have been assigned green and blue respectively. The large amounts of green and blue in the image show that there is a large amount of Hydrogen and Oxygen in the nebula. On 26 October 2004, the NASA/ESA Cassini-Huygens spacecraft captured a false-color image of Titan, Saturn's largest moon.<ref>{{Cite web |last=JPL |first=Carolina Martinez |title=NASA - First Close Encounter of Saturn's Hazy Moon Titan |url=https://www.nasa.gov/mission_pages/cassini/media/cassini-102504.html |access-date=2022-03-09 |website=www.nasa.gov |language=en |archive-date=14 July 2022 |archive-url=https://web.archive.org/web/20220714210218/https://www.nasa.gov/mission_pages/cassini/media/cassini-102504.html |url-status=dead }}</ref> The image was captured in Ultraviolet and Infrared wavelengths, both invisible to the human eye.<ref>{{Cite web |last=Hadhazy |first=Adam |title=What are the limits of human vision? |url=https://www.bbc.com/future/article/20150727-what-are-the-limits-of-human-vision |access-date=2022-03-09 |website=www.bbc.com |language=en}}</ref> In order to provide a visual representation, false color techniques were used. The infrared data was mapped to red and green colors, and ultraviolet mapped to blue.<ref>{{Cite web |title=NASA - Titan in False Color |url=https://www.nasa.gov/mission_pages/cassini/multimedia/pia06139.html |access-date=2022-03-09 |website=www.nasa.gov |language=en |archive-date=9 March 2022 |archive-url=https://web.archive.org/web/20220309192840/https://www.nasa.gov/mission_pages/cassini/multimedia/pia06139.html |url-status=dead }}</ref>
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