Brightness
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2008-05-14T19:08:23Z
Neelix
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{{for|the folk album|The Brightness}}
'''Brightness''' (also called '''effulgence''') is an attribute of [[visual perception]] in which a source appears to emit a given amount of [[light]]. In other words, brightness is the perception elicited by the [[luminance]] of a visual target. This is a [[subjective]] [[attribute]]/[[property]] of an object being observed.
==Terminology==
"Brightness" was formerly used as a synonym for the [[photometry (optics)|photometric]] term ''[[luminance]]'' and (incorrectly) for the [[radiometric]] term ''[[radiance]]''.
As defined by the US ''Federal Glossary of Telecommunication Terms'' ([[Federal Standard 1037C|FS-1037C]]), "brightness" should now be used only for non-quantitative references to physiological sensations and perceptions of light.<ref>“[http://www.its.bldrdoc.gov/fs-1037/dir-005/_0719.htm Brightness]” in Federal Standard 1037C, the ''Federal Glossary of Telecommunication Terms'' (1996)</ref>
A given target luminance can elicit different perceptions of brightness in different contexts; see, for example, [[White's illusion]] and [[Wertheimer]]-Benary illusion.
In the [[RGB color space]], brightness can be thought of as the [[arithmetic mean]] ''μ'' of the '''R'''ed, '''G'''reen, and '''B'''lue color coordinates (although some of the three components make the light seem brighter than others, which, again, may be compensated by some display systems automatically):<ref>[http://www.poynton.com/notes/colour_and_gamma/ColorFAQ.html#RTFToC36 What are HSB and HLS?], Charles Poynton: "The usual formulation of HSB and HLS compute so-called "lightness" or "brightness" as (R+G+B)/3. This computation conflicts badly with the properties of colour vision, as it computes yellow to be about six times more intense than blue with the same "lightness" value (say L=50)."</ref>
:<math>\mu = {R + G + B \over 3 }</math>
Brightness is also a color coordinate in the HSB or [[HSV color space]] (hue, [[Saturation (color theory)|saturation]], and brightness or value).
With regard to [[star]]s, brightness is quantified as [[apparent magnitude]] and [[absolute magnitude]].
==Brightness of sounds==
The term "brightness" is also used in discussions of sound [[timbre]]s, in a rough analogy with visual brightness. Timbre researchers consider brightness to be one of the perceptually strongest distinctions between sounds<ref>D. Wessel, [http://mediatheque.ircam.fr/articles/textes/Wessel78a/ Timbre space as a musical control structure], Computer Music Journal, 3 (1979), pp. 45–52.</ref>, and formalize it acoustically as an indication of the amount of high-frequency content in a sound, using a measure such as the [[spectral centroid]].
==See also==
* [[Luma (video)]]
* [[Luminance (relative)]]
==Notes==
{{reflist}}
==External links==
{{Wiktionarypar|brightness}}
* [http://www.poynton.com/ColorFAQ.html Poynton's Color FAQ]
[[Category:vision]]
[[Category:Photometry]]
[[bg:Яркост]]
[[de:Helligkeit]]
[[ko:명도]]
[[it:Luminosità (teoria dei colori)]]
[[hu:Világosság]]
[[pt:Brilhância]]
[[th:ความสว่าง]]
[[vi:Độ trắng]]
[[zh:明度]]