Lightness Scales

The early Munsell lightness scale assumed that lightness is just proportional to the square root of luminance. This is approximately correct when the samples of a grey scal are viewed on a white background. If the samples are viewed against a background of middle grey the equation must be modified (Godlove 1933, Munsell 1933) to take into account the reflectance of the baclground, A slight modification of this relationship led to the Munsell Value scale (Newhall 1943), Later Glasser showed that a cube-root function is a good approximation to the Munsell value equation for reflectance greater than 1%

Examples of lightness equations are: