A white reference (W) image
(99.9% reflectance) was acquired from a white reference ceramic tile, and a dark reference (D) image (0% reflectance) was
obtained with the light source off and the camera lens completely
covered with its opaque cap. These two reference images were
then used to calculate a relative reflectance image (R) of the
sample using the following equation:
R ¼ ð Þ R02D =ð Þ ð W2D 1