Brightness is an attribute of
visual perceptionin which a source appears to emit or reflect a given amount of light. In other words, brightness is the perception elicited by the luminanceof a visual target. This is a subjective attribute/ propertyof an object being observed.
"Brightness" was formerly used as a synonym for the photometric term "
luminance" and (incorrectly) for the radiometricterm " radiance".As defined by the US "Federal Glossary of Telecommunication Terms" (FS-1037C), "brightness" should now be used only for non-quantitative references to physiological sensations and perceptions of light. [“ [http://www.its.bldrdoc.gov/fs-1037/dir-005/_0719.htm Brightness] ” in Federal Standard 1037C, the "Federal Glossary of Telecommunication Terms" (1996)]
A given target luminance can elicit different perceptions of brightness in different contexts; see, for example,
White's illusionand Wertheimer-Benary illusion.
RGB color space, brightness can be thought of as the arithmetic mean"μ" of the Red, Green, and Blue 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): [ [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)."] :
Brightness is also a color coordinate in the HSB or
HSV color space(hue, saturation, and brightness or value).
With regard to
stars, brightness is quantified as apparent magnitudeand absolute magnitude.
Brightness of sounds
The term "brightness" is also used in discussions of sound
timbres, in a rough analogy with visual brightness. Timbre researchers consider brightness to be one of the perceptually strongest distinctions between sounds [D. Wessel, [http://mediatheque.ircam.fr/articles/textes/Wessel78a/ Timbre space as a musical control structure] , Computer Music Journal, 3 (1979), pp. 45–52.] , 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.
* [http://www.poynton.com/ColorFAQ.html Poynton's Color FAQ]
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