
Figure 20.2
Luminance and lightness.
The dependence of lightness (L*) or value (V) upon rela-
tive luminance (Y) has been modeled by polynomials, power functions, and logarithms. In all of
these systems, 18% "mid-gray" has lightness about halfway up the perceptual scale. For details,
see Fig. 2 (6.3) in Wyszecki and Stiles,
Color Science
(cited on page 231).
The L* symbol is pronounced
EL-star.
Lightness (CIE L*)
In
Contrast sensitivity,
on page 198, I explained that
vision has a nonlinear perceptual response to lumi-
nance. Vision scientists have proposed many functions
that relate relative luminance