In this thesis, a modified BRDF model for wide-angle scattering is presented. The proposed model is developed from empirical observations of several BRDF models. The model is an extention of the classical microfacet models. By replacing the two cosines of elevation angles with functions and exponent parameters, our model is able to give a special characteristic which we have not found in any other BRDF models. The characteristic at wide-angle scattering can be, for example, seen on the polyethylene material. In addition, our proposed model can greatly improve relative error from the reference model. The average relative error improvement is about 20 ercent for a cosine weighted error metric,E1 , and 10 percent for a logarithmic error metric, E 2,. Moreover, we also introduce a new optimization approach for the proposed terms. This approach can do optimization so that our proposed model gives at least an equivalent error to the reference model.