Separating Partially-Polarized Diffuse and Specular Reflection Components under Unpolarized Light Sources

Separating diffuse and specular reflection components observed on an object surface is important for preprocessing of various computer vision techniques. Conventionally, diffuse-specular separation based on the polarimetric and color clues assumes that the diffuse/specular reflection components are unpolarized/partially polarized under unpolarized light sources. However, the diffuse reflection component is partially polarized in fact, because the diffuse reflectance is maximal when the polarization direction is parallel to the outgoing plane. Accordingly, we propose a method for separating partially-polarized diffuse and specular reflection components on the basis of the polarization reflection model and the dichromatic reflection model. In particular, our method enables us not only to achieve diffuse-specular separation but also to estimate the polarimetric properties of the object surface from a single color polarization image. We experimentally confirmed that our method performs better than the method assuming unpolarized diffuse reflection components.