Brightness
Encyclopedia
Brightness is an attribute of visual perception
in which a source appears to be radiating or reflecting 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.
root with a closely related meaning, * "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.
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):
Brightness is also a color coordinate in the HSB or HSV color space (hue, saturation
, and brightness or value).
With regard to star
s, brightness is quantified as apparent magnitude
and absolute magnitude
.
s, in a rough analogy with visual brightness. Timbre researchers consider brightness to be one of the perceptually strongest distinctions between sounds, 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
.
Visual perception
Visual perception is the ability to interpret information and surroundings from the effects of visible light reaching the eye. The resulting perception is also known as eyesight, sight, or vision...
in which a source appears to be radiating or reflecting light
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
. In other words, brightness is the perception elicited by the luminance
Luminance
Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through or is emitted from a particular area, and falls within a given solid angle. The SI unit for luminance is candela per square...
of a visual target. This is a subjective attribute/property of an object being observed.
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 *, ultimately from a PIEProto-Indo-European language
The Proto-Indo-European language is the reconstructed common ancestor of the Indo-European languages, spoken by the Proto-Indo-Europeans...
root with a closely related meaning, * "white, bright".
"Brightness" was formerly used as a synonym for the photometric
Photometry (optics)
Photometry is the science of the measurement of light, in terms of its perceived brightness to the human eye. It is distinct from radiometry, which is the science of measurement of radiant energy in terms of absolute power; rather, in photometry, the radiant power at each wavelength is weighted by...
term luminance
Luminance
Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through or is emitted from a particular area, and falls within a given solid angle. The SI unit for luminance is candela per square...
and (incorrectly) for the radiometric term radiance
Radiance
Radiance and spectral radiance are radiometric measures that describe the amount of radiation such as light or radiant heat that passes through or is emitted from a particular area, and falls within a given solid angle in a specified direction. They are used to characterize both emission from...
.
As defined by the US Federal Glossary of Telecommunication Terms (FS-1037C
Federal Standard 1037C
Federal Standard 1037C, titled Telecommunications: Glossary of Telecommunication Terms is a United States Federal Standard, issued by the General Services Administration pursuant to the Federal Property and Administrative Services Act of 1949, as amended....
), "brightness" should now be used only for non-quantitative references to physiological sensations and perceptions of light.
A given target luminance can elicit different perceptions of brightness in different contexts; see, for example, White's illusion
White's illusion
White's illusion is an optical illusion illustrating the fact that the same target luminance can elicit different perceptions of brightness in different contexts....
.
In the RGB color space
RGB color space
An RGB color space is any additive color space based on the RGB color model. A particular RGB color space is defined by the three chromaticities of the red, green, and blue additive primaries, and can produce any chromaticity that is the triangle defined by those primary colors...
, brightness can be thought of as the arithmetic mean
Arithmetic mean
In mathematics and statistics, the arithmetic mean, often referred to as simply the mean or average when the context is clear, is a method to derive the central tendency of a sample space...
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):
Brightness is also a color coordinate in the HSB or HSV color space (hue, saturation
Saturation (color theory)
In colorimetry and color theory, colorfulness, chroma, and saturation are related but distinct concepts referring to the perceived intensity of a specific color. Colorfulness is the degree of difference between a color and gray. Chroma is the colorfulness relative to the brightness of another color...
, and brightness or value).
With regard to star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
s, brightness is quantified as apparent magnitude
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...
and absolute magnitude
Absolute magnitude
Absolute magnitude is the measure of a celestial object's intrinsic brightness. it is also the apparent magnitude a star would have if it were 32.6 light years away from Earth...
.
Brightness of sounds
The term "brightness" is also used in discussions of sound timbreTimbre
In music, timbre is the quality of a musical note or sound or tone that distinguishes different types of sound production, such as voices and musical instruments, such as string instruments, wind instruments, and percussion instruments. The physical characteristics of sound that determine the...
s, in a rough analogy with visual brightness. Timbre researchers consider brightness to be one of the perceptually strongest distinctions between sounds, 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
Spectral centroid
The spectral centroid is a measure used in digital signal processing to characterise a spectrum. It indicates where the "center of mass" of the spectrum is...
.