Lightness
perceived luminance
see color science, luminance, cielab, gamma correction, math notation, luma
notation \(J\) (used in CIECAM02), \(L^*\) (used in cielab and CIELUV)
definition in color science, lightness is a linear prediction of the perceived brightness of a color by the human eye --- Wikipedia
when green luminance equals red luminance equals blue luminance, green lightness is greater than red lightness is greater than blue lightness
cameras automatically set their exposure to achieve an average cie 1931› xyz luminance of \(Y = 0.184\) in the image, which is a lightness (perceived luminance) of \(50\%\) and a cielab lightness of \(50\%\). this is why so-called 18% gray cards can be used to calibrate exposure --- https://youtu.be/a4kU3ZUX44Y and https://en.wikipedia.org/wiki/Middle_gray
representation
