WordNet

the location of a visual perception along a continuum from black to white
intelligence as manifested in being quick and witty (同)cleverness, smartness
high level or degree; the property of being intense (同)intensiveness
the amount of energy transmitted (as by acoustic or electromagnetic radiation); "he adjusted the intensity of the sound"; "they measured the stations signal strength" (同)strength, intensity level
the tendency for a visual object to be perceived as having the same brightness under widely different conditions of illumination
the strength of a radio wave picked up by a radio telescope

PrepTutorEJDIC

輝き;明るさ;(自の)あざやかさ
(感情・行動・熱・色などの)『強烈さ』,熱烈さ,強度

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2015/06/22 19:16:30」(JST)

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Decreasing brightness with depth (underwater photo as example)

Brightness is an attribute of visual perception in which a source appears to be radiating or reflecting light.^[1] 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 and one of the color appearance parameters of color appearance models.

Terminology

The adjective bright derives from an Old English beorht with the same meaning via metathesis giving Middle English briht. The word is from a Common Germanic *berhtaz, ultimately from a PIE root with a closely related meaning, *bhereg- "white, bright". "Brightness" was formerly used as a synonym for the photometric term luminance and (incorrectly) for the radiometric term 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.^[2]

A given target luminance can elicit different perceptions of brightness in different contexts; see, for example, White's illusion.

In the 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):^[3]

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 magnitude and absolute magnitude.

Brightness is, at least in some respects, the antonym of darkness.

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,^[4] 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.

Notes

^ Merriam-Webster.com Merriam-Webster Dictionary definition of bright
^ “Brightness” in Federal Standard 1037C, the Federal Glossary of Telecommunication Terms (1996)
^ 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)."
^ D. Wessel, Timbre space as a musical control structure, Computer Music Journal, 3 (1979), pp. 45–52.

External links

Poynton's Color FAQ

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