The relationship between the Kubelka–Munk (K–M) and the transport scattering coefficient is obtained through a semi-empirical approach. This approach gives the same result as that given by Gate [Appl. Opt. 13, 236 (1974)] when the incident beam is diffuse. This result and those given by Star et al. [Phys. Med. Biol. 33, 437 (1988)] and Brinkworth [Appl. Opt. 11, 1434 (1972)] are compared with the exact solution of the radiative transfer equation over a large range of optical properties. It is found that the latter expressions, which include an absorption component, do not give accurate results over the range considered. Using the semi-empirical approach, the relationship between the K–M and the transport scattering coefficient is derived for the case where the incident light is collimated. It is shown that although the K–M equation is derived based on diffuse incident light, it can also represent very well the reflectance from a slab of infinite thickness when the incident light is collimated. However, in this case the relationship between the coefficients has to include a function that is dependent on the anisotropy factor. Analysis indicates that the K–M transform achieves the objective of obtaining a measure that gives the ratio of absorption to scattering effects for both diffuse and collimated incident beams over a large range of optical properties.
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