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Lightness (color)
 
 
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Lightness is a property of a color
Color

Color or colour is the visual perception property corresponding in humans to the categories called red, yellow, blue and others....
, or a dimension of a color space
Color space

A color model is an abstract mathematical model describing the way colors can be represented as tuples of numbers, typically as three or four values or color components ....
, that is defined in a way to reflect the subjective brightness perception of a color for humans. The Munsell value is an example of a lightness scale.

Value is a measure of where a particular color lies along the lightness–darkness axis. A color's value is its amplitude
Amplitude

Amplitude is the magnitude of change in the oscillating variable, with each oscillation, within an oscillating system. For instance, sound waves are oscillations in atmospheric pressure and their amplitudes are proportional to the change in pressure during one oscillation....
. Various color models
Color models

A color model is an abstract mathematical model describing the way colors can be represented as tuples of numbers, typically as three or four values or color components....
 have an explicit term which places the color on a scale from utter black
Black

Black is the color of objects that do not emit or reflection light in any part of the visible spectrum; they absorb all such frequencies of light....
 to pure white
White

White is a color, the Color vision#Physiology of color perception which is evoked by light that stimulates all three types of color sensitive cone cells in the human eye in near equal amount and with high brightness compared to the surroundings....
.






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Lightness is a property of a color
Color

Color or colour is the visual perception property corresponding in humans to the categories called red, yellow, blue and others....
, or a dimension of a color space
Color space

A color model is an abstract mathematical model describing the way colors can be represented as tuples of numbers, typically as three or four values or color components ....
, that is defined in a way to reflect the subjective brightness perception of a color for humans. The Munsell value is an example of a lightness scale.

Value is a measure of where a particular color lies along the lightness–darkness axis. A color's value is its amplitude
Amplitude

Amplitude is the magnitude of change in the oscillating variable, with each oscillation, within an oscillating system. For instance, sound waves are oscillations in atmospheric pressure and their amplitudes are proportional to the change in pressure during one oscillation....
. Various color models
Color models

A color model is an abstract mathematical model describing the way colors can be represented as tuples of numbers, typically as three or four values or color components....
 have an explicit term which places the color on a scale from utter black
Black

Black is the color of objects that do not emit or reflection light in any part of the visible spectrum; they absorb all such frequencies of light....
 to pure white
White

White is a color, the Color vision#Physiology of color perception which is evoked by light that stimulates all three types of color sensitive cone cells in the human eye in near equal amount and with high brightness compared to the surroundings....
. The HSV color model and Munsell color model
Munsell color system

In colorimetry, the Munsell color system is a color space that specifies colors based on three color dimensions: hue, value , and chroma . It was created by Professor Albert Henry Munsell in the first decade of the 20th century....
 have an explicit value, while the HSL color model uses a related parameter called lightness instead.

In the HSV and Munsell color models, a color with a low value is nearly black, while one with a high value is the pure color.

The image shows three hue
Hue

Hue is one of the main properties of a color described with names such as "red", "yellow", etc. The two other main properties are lightness and colorfulness....
s in the Munsell color model. Each color differs in value from top to bottom in equal perception steps. The right column undergoes a dramatic change in perceived color.

In subtractive color
Subtractive color

A subtractive color model explains the mixing of paints, dyes, inks, and natural colorants to create a range of colors, where each such color is caused by the mixture absorbing some wavelengths of light and reflecting others....
, i.e. paints, value changes can be achieved by adding black or white to the color. However, this also reduces saturation.

Chiaroscuro
Chiaroscuro

Chiaroscuro is a term in art for a contrast between light and dark. The term is usually applied to bold contrasts affecting a whole composition, but is also more technically used by artists and art historians for the use of effects representing contrasts of light, not necessarily strong, to achieve a sense of volume in modeling three-di...
 and Tenebrism
Tenebrism

Tenebrism, from the Italian language tenebroso , is a style of painting using violent contrasts of light and Darkness. A heightened form of chiaroscuro, it creates the look of figures emerging from the dark....
 both take advantage of dramatic contrasts of value to heighten drama in art. Artists may also employ shading
Shading

Shading refers to wikt:depicting depth in 3D models or illustrations by varying levels of darkness....
, subtle manipulation of value.

Relationship between lightness, value, and luminance

The Munsell value has long been used as a perceptually uniform lightness scale. A question of interest is the relationship between the Munsell value scale and the relative luminance. Aware of the Weber–Fechner law
Weber–Fechner law

The Weber?Fechner law attempts to describe the relationship between the physical magnitudes of Stimulus and the perceived intensity of the stimuli....
, Munsell remarked "Should we use a logarithmic curve or curve of squares?" Neither option turned out to be quite correct; scientists eventually converged on a roughly cube-root curve, consistent with the Stevens power law for brightness perception, reflecting the fact that lightness is proportional to the number of nerve impulses per nerve fiber per unit time. The remainder of this section is a chronology of lightness approximations, leading to CIELAB.

Note: Munsell's V runs from 0 to 10, while Y typically runs from 0 to 100 (often interpreted as a percent). Typically, the relative luminance is normalized so that the "reference white" (say, magnesium oxide
Magnesium oxide

Magnesium oxide, or magnesia, is a white solid mineral that occurs naturally as periclase and is a source of magnesium . It has an empirical formula of ....
) has a tristimulus value of Y=100. Since the reflectance of magnesium oxide (MgO) relative to the perfect reflecting diffuser is 97.5%, V=10 corresponds to Y=100/97.5%˜102.6 if MgO is used as the reference.

1920: Priest et al provide a basic estimate of the Munsell value (with Y running from 0 to 1 in this case):

1933: Munsell, Sloan, and Godlove launch a study on the Munsell neutral value scale, considering several proposals relating the relative luminance to the Munsell value, and suggest:

1943: Newhall, Nickerson, and Judd prepare a report for the Optical Society of America
Optical Society of America

The Optical Society of America is a scientific society dedicated to advancing the study of light?optics and photonics?in theory and application, by means of worldwide research, academic publishing, Academic conference and Trade fair, partnership with industry, and the education of new generations of scientists....
. They suggest a quintic parabola (relating the reflectance in terms of the value):

1943: Using Table II of the O.S.A. report, Moon and Spencer express the value in terms of the luminance:

1944: Saunderson and Milner introduce a subtractive constant in the previous expression, for a better fit to the Munsell value. Later, Jameson and Hurvich claim that this corrects for simultaneous contrast effect
Contrast effect

A contrast effect is the enhancement or diminishment, relative to normal, of perception, cognition and related performance as a result of immediately previous or simultaneous exposure to a Stimulus of lesser or greater value in the same dimension....
s.

1955: Ladd and Pinney of Eastman Kodak
Eastman Kodak

Eastman Kodak Company is a multinational corporation public company which produces imaging and photography materials and equipment. Long known for its wide range of photographic film products, Kodak is re-focusing on two major markets: digital photography and digital printing....
 are interested in the Munsell value as a perceptually uniform lightness scale for use in television
Television

Television is a widely used telecommunication mass-media for transmitting and receiving moving , either monochrome or color, usually accompanied by sound....
. After considering one logarithmic and five power-law functions (per Stevens' power law
Stevens' power law

Stevens' power law is a proposed relationship between the magnitude of a physical stimulus and its perceived intensity or strength. It is often considered to supersede the Weber-Fechner law on the basis that it describes a wider range of sensations, although critics argue that the validity of the law is contingent on the virtue of approaches...
), they relate value to reflectance by raising the reflectance to the power of 0.352:

Realizing this is quite close to the cube root, they simplify it to

1958: Glasser et al define the lightness as ten times the Munsell value (so that the lightness ranges from 0 to 100):

1964: Wyszecki simplifies this to:

This formula approximates the Munsell value function for (it is not applicable for Y<1%) and is used for the CIE 1964 color space
CIE 1964 color space

The CIE 1964 color space, CIEUVW is based on the CIE 1960 color space:where is the white point and is the luminous tristimulus value of the object....
.

1976: CIELAB uses the following formula:

where is the Y tristimulus value of a "specified white object" and is subject to the restriction . Pauli removes this restriction by computing a linear extrapolation which maps Y/Yn=0 to L*=0 and is tangent to the formula above at the point at which the linear extension takes effect. First, the transition point is determined to be , then the slope of is computed. This gives the two-part function:

The lightness is then .

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