Modification of the Maxwell-Beard bidirectional reflectance distribution function

A modification to the mathematical representation of shadowing and obscuration (SO) in the Maxwell-Beard BRDF model is proposed to better represent actual SO data and subsequently improve the accuracy of model predicted values of BRDF. The SO function is an empirical dual peak mathematical expression originally developed for smooth first surface layer opaque material, such as semi-gloss and gloss paints. Adding variability to forward scattering of the SO function allows a better fit to more sample types. The result is a more accurate prediction of BRDF values for model non-compliant samples such as brick, concrete, asphalt, and paints with high concentrations of extender pigment. Data were collected and analyzed for both model compliant and non-compliant samples. The proposed model changes were implemented through use of an interactive spreadsheet. Results for compliant and non-compliant samples were compared using the original and modified model. Model compliant samples showed little improvement, while non-compliant samples often showed marked improvement.