where DL⁄, Da⁄ and Db⁄ are the difference between the two samples
in L⁄, a⁄ and b⁄, respectively. The perception of the color difference
DE⁄ varies according to the observed color and the sensitivity
of the human eye. The human eye only distinguishes color difference
if DE⁄ is larger than 1–3. For some colors, mainly blues, DE⁄
values of 1 can be detected, but for other colors, such as red, the
same DE⁄ may not be perceptible (Bodart, de