[7][8][9] 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.
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.
When Albert Henry Munsell was developing his color system, he tried to ascertain the relation between luminance and perceived lightness.
[13][14] 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 1976 the International Commission on Illumination defined the CIELAB color space,[17] an extension of which would become the standard for the coming decades in a variety of applications.