Modeling specular goniochromatic materials using near-specular and diffuse reflectance

Accurate characterization of goniochromatic materials, which show angle-dependent color variations, is a challenging task due to their complex optical behavior resulting from diffraction, thin-film interference, and structural coloration. The bidirectional reflectance distribution function (BRDF) is an effective tool for characterizing these materials. In this work, we examine a recently proposed empirical goniochromatic BRDF model and assess its performance for our highly specular and highly goniochromatic samples. Using a few measurements obtained from a handheld goniospectrophotometer, we propose a separation between the near-specular and diffuse components. This modification significantly enhances the original model's performance, enabling more accurate representation and analysis of our goniochromatic materials.