Middle gray

Following the Weber–Fechner law, 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 had to be used to find the middle gray.{{cite book | title = The New International Encyclopædia |author1=Daniel Coit Gilman |author2=Harry Thurston Peck |author3=Frank Moore Colby |name-list-style=amp | publisher = Dodd, Mead and Company | year = 1903 | url =https://archive.org/details/newinternationa06gilm/page/128}} That is equivalent to a relative luminance of 12.9% (　).

When Albert Henry Munsell 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?'{{cite journal|title=The early development of the Munsell system|first=Rolf G.|last=Kuehni|volume=27|issue=1|pages=20–27|doi=10.1002/col.10002|date=February 2002|journal=Color Research & Application}} 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 balancedFirst the photocells are illuminated by lamps and their outputs are balanced without the sample present; then the sample is placed at one cell and the lamp illuminating the other cell is moved further away until the outputs rebalance. For a more detailed description see K.S. Gibson, Photoelectric spectrophotometry using the null method. that the shades in Munsell's 1915 atlas followed a square root curve, which was later confirmed by extensive experiments.{{Cite journal|first1=Irwin G.|last1=Priest|last2=Gibson|first2=K.S.|last3=McNicholas|first3=H.J.|title=An examination of the Munsell color system. I: Spectral and total reflection and the Munsell scale of Value|journal=Technical Paper 167|page=27|issue=3|publisher=United States Bureau of Standards|date=September 1920}}Munsell AEO, Sloan LL, Godlove IH. Neutral value scales I, Munsell neutral value scale. J Opt Soc Am 1933;23:394 – 401 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.{{Cite journal|first1=Irwin G.|last1=Priest|last2=Gibson|first2=K.S.|last3=McNicholas|first3=H.J.|title=An examination of the Munsell color system. I: Spectral and total reflection and the Munsell scale of Value|journal=Technical Paper 167|page=27|issue=3|publisher=United States Bureau of Standards|date=September 1920}}

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."Munsell AEO, Sloan LL, Godlove IH. Neutral value scales I, Munsell neutral value scale. J Opt Soc Am 1933;23:394 – 401

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 defined the CIELAB color space,CIE Colorimetry–Part 4: 1976 L* a* b* Colour Space an extension of which would become the standard for the coming decades in a variety of applications.H. Pauli, Proposed extension of the CIE recommendation on "Uniform color spaces, color difference equations, and metric color terms"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; see Lightness § 1933 for details.

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.

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Category:Science of photography