The change in reflectance of a diffuser, due to a known change in the ratio of its absorption and scattering coefficients, can be predicted from the simple Kubelka–Munk equations or from Giovanelli’s more detailed theory. These predictions may differ by up to about 0.01 in reflectance. Differences of this magnitude have also been found between reflectance changes predicted by Giovanelli’s theory and measured changes. There is evidence that diffuser theory cannot give greater accuracy unless based on a scattering distribution which is more realistic than isotropic scattering. In the absence of such a theory, the Kubelka–Munk theory is as reliable as any for practical reflectance problems with opaque diffusers.
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