Editing False color (section)

=== True color ===
The concept behind '''true color''' can help in understanding false color. An image is called a ''true-color'' image when it offers a natural [[color]] rendition, or when it comes close to it. This means that the colors of an object in an image [[color vision|appear to a human observer]] the same way as if this same observer were to directly view the object: A green tree appears green in the image, a red apple red, a blue sky blue, and so on.<ref name="autogenerated1">{{cite web|url=http://www.crisp.nus.edu.sg/~research/tutorial/opt_int.htm |title=Principles of Remote Sensing - Centre for Remote Imaging, Sensing and Processing, CRISP |publisher=www.crisp.nus.edu.sg |access-date=2012-09-01}}</ref> 

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| header            = Two [[Landsat]] satellite images showing the same region: <br/>Land around the [[Chesapeake Bay]]<ref>{{cite web |url=http://landsat.gsfc.nasa.gov/?page_id=11/compositor/ |title=The Landsat 7 Compositor |publisher=landsat.gsfc.nasa.gov |date=2011-03-21 |access-date=2012-09-01 |archive-date=21 September 2013 |archive-url=https://web.archive.org/web/20130921121348/http://landsat.gsfc.nasa.gov/?page_id=11%2Fcompositor%2F |url-status=dead }}</ref>
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| image1    = True-color-image.png
| caption1  = This true-color image shows the area in actual colors, e.g., the vegetation appears in green. It covers the full [[visible spectrum]] using the red, green and blue / green spectral bands of the satellite mapped to the [[RGB color model|RGB color space]] of the image.
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| image2    = False-color-image.png
| caption2  = The same area as a false-color image using the [[infrared|near infrared]], red and green spectral bands mapped to RGB – this image shows vegetation in a red tone, as vegetation reflects most light in the near infrared. 
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[[File:Burns cliff.jpg|thumb|Burns Cliff inside of [[Endurance (crater)|Endurance crater]] on [[Mars]]. The color is approximate true color because, instead of the red spectral band, infrared was used. The result is a metameric failure in the color of the sky, which is slightly green in the image – had a [[human]] observer been present, then that person would have perceived the actual sky color to have a bit more orange in it. The ''Opportunity'' rover which captured this image does have a red filter, but it is often not used, due to the higher scientific value of images captured using the infrared band and the constraints of data transmission.]]

Absolute true-color rendering is impossible.<ref name="universetoday1">{{cite web|author=Nancy Atkinson |url=http://www.universetoday.com/11863/true-or-false-color-the-art-of-extraterrestrial-photography/ |title=True or False (Color): The Art of Extraterrestrial Photography |publisher=www.universetoday.com |date=2007-10-01 |access-date=2012-09-01}}</ref> There are three major sources of color error ([[Metamerism (color)|metameric]] failure):
* Different [[Spectral sensitivity|spectral sensitivities]] of the human eye and of an [[image capture device]] (e.g. a [[camera]]).
* Different spectral emissions / reflections of the object and of the [[image render process]] (e.g. a [[Printer (computing)|printer]] or [[Computer monitor|monitor]]).
* Differences in [[spectral irradiance]] in the case of reflective images (e.g. photo prints) or reflective objects – see [[color rendering index]] (CRI) for details.
The result of a metameric failure would be for example an image of a green tree which shows a different shade of green than the tree itself, a different shade of red for a red apple, a different shade of blue for the blue sky, and so on. [[Color management]] (e.g. with [[ICC profile]]s) can be used to mitigate this problem within the physical constraints.

Approximate true-color images gathered by spacecraft are an example where images have a certain amount of metameric failure, as the spectral bands of a spacecraft's camera are chosen to gather information on the physical properties of the object under investigation, and are not chosen to capture true-color images.<ref name="universetoday1"/>

{{Wide image|MarsEndurance.jpg|1024px|This approximate true-color [[panorama]] shows the impact crater [[Endurance (crater)|Endurance]] on [[Mars]]. It was taken by the panoramic camera on the ''[[Opportunity rover|Opportunity]]'' rover and is a composite of a total of 258 images taken in the 480, 530 and 750 [[nanometer]] spectral bands (blue / green, green and near infrared).}}