50%
CIELAB
The CIELAB color space, also referred to as ''L*a*b*'', is a color space defined by the International Commission on Illumination (abbreviated CIE) in 1976. It expresses color as three values: ''L*'' for perceptual lightness and ''a*'' and ''b* ...
lightness
(
Y = %)
In
photography
Photography is the visual arts, art, application, and practice of creating images by recording light, either electronically by means of an image sensor, or chemically by means of a light-sensitive material such as photographic film. It is empl ...
,
painting
Painting is a Visual arts, visual art, which is characterized by the practice of applying paint, pigment, color or other medium to a solid surface (called "matrix" or "Support (art), support"). The medium is commonly applied to the base with ...
, and other visual arts, middle gray or middle grey is a tone that is perceptually about halfway between black and white on a
lightness
Lightness is a visual perception of the luminance (L) of an object. It is often judged relative to a similarly lit object. In colorimetry and color appearance models, lightness is a prediction of how an illuminated color will appear to a stand ...
scale; in photography and printing, it is typically defined as 18% reflectance in visible light.
Light meters, cameras, and pictures are often calibrated using an 18%
gray card
A gray card is a middle gray reference, typically used together with a reflective light meter, as a way to produce consistent image exposure and/or color in video production, film, and photography.
A gray card is a flat object of a neutral-gr ...
[''Film and Its Techniques'' by Raymond Spottiswoode] or a
color reference card such as a
ColorChecker. On the assumption that 18% is similar to the average reflectance of a scene, a gray card can be used to estimate the required exposure of the film.
[
]
History
Following the Weber–Fechner law
The Weber–Fechner laws are two related scientific law, scientific laws in the field of psychophysics, known as Weber's law and Fechner's law. Both relate to human perception, more specifically the relation between the actual change in a physica ...
, at the start of the 20th century human lightness perception was assumed to be logarithmic. In 1903, ''The New International Encyclopædia'' illustrated this concept by stating that given a black and white with a luminance ratio of 1:60 ( : ), the geometric mean
In mathematics, the geometric mean is a mean or average which indicates a central tendency of a finite collection of positive real numbers by using the product of their values (as opposed to the arithmetic mean which uses their sum). The geometri ...
had to be used to find the middle gray. That is equivalent to a relative luminance of 12.9% ( ).
When Albert Henry Munsell
Albert Henry Munsell (January 6, 1858 – June 28, 1918) was an American painter, teacher of art, and the inventor of the Munsell color system.
He was born in Boston, Massachusetts, attended and served on the faculty of Massachusetts Normal Art ...
was developing his color system, he tried to ascertain the relation between luminance and perceived lightness. As early as 1906, he wrote: 'Should we use logarithmic curve or curve of squares?' In 1920 Priest, Gibson, and McNicholas showed using both a König-Martens spectrophotometer and an apparatus designed by Gibson where the outputs of two photocells are balanced that the shades in Munsell's 1915 atlas followed a square root curve, which was later confirmed by extensive experiments. In Munsell's system, the shades of neutral gray were labelled N1 to N9, with N5 in the middle and 0 and 10 denoting the unachievable ideal black and perfect white.
In 1933, Alexander Ector Orr Munsell (Albert Henry Munsell's son) found "that a series of neutral reflecting surfaces whose reflectances are...18.0...and 100.0 percent...form for the average observer a series of equal differences in value."
From the 1930s onward various lightness curves were proposed, but halfway through the 20th century, the proposals settled on cube-root-based curves. In 1976 the International Commission on Illumination
The International Commission on Illumination (usually abbreviated CIE for its French name Commission internationale de l'éclairage) is the international authority on light, illumination, colour, and colour spaces. It was established in 1913 a ...
defined the CIELAB color space
The CIELAB color space, also referred to as ''L*a*b*'', is a color space defined by the International Commission on Illumination (abbreviated CIE) in 1976. It expresses color as three values: ''L*'' for perceptual lightness and ''a*'' and '' ...
, an extension of which would become the standard for the coming decades in a variety of applications.[Kenichiro Masaoka, Fu Jiang, Mark D. Fairchild & Rodney L. Heckaman, ''Analysis of color volume of multi-chromatic displays using gamut rings''] Following research in the 80s and 90s, more and more advanced models of color vision were developed, the first major step being CIECAM97s
A color appearance model (CAM) is a mathematical model that seeks to describe the perceptual aspects of human color vision, i.e. viewing conditions under which the appearance of a color does not tally with the corresponding physical measurement of ...
; see Lightness § 1933 for details.
Table of middle grays
Below are various "middle" grays based on various criteria.
The shades in the rightmost column will only be correct if viewed on a calibrated monitor.
Note that LCD screens, even when correctly calibrated, often have a brightness that varies considerably depending on the viewing angle.
Quarter luminance list (typical monitor calibrated to 2.2 gamma, 50% luminance gray has RGB hex 0xBA value, which is 0.5^(1/2.2)*255)
* Context-dependent; an estimate is displayed here taking the environment where it appears in the article into account and assuming a neutrally lit surround of 200 cd/m2.
References
{{DEFAULTSORT:Middle Gray
Science of photography