A Portable Measurement System for Spatially-Varying Reflectance Using Two Handheld Cameras

In this paper, we propose a system that can measure the spatially-varying reflectance of real materials. Our system uses two handheld cameras, a small LED light, a turning table, and a chessboard with markers. The two cameras are used as a view and light cameras respectively to acquire incoming and outgoing light directions simultaneously, and the brightness at each position on the target material. The reflectance is approximated by using the Ward BRDF (Bidirectional Reflectance Distribution Function) model. The normal directions and all model parameters at each position on the material are estimated by non-linear optimization. As the result of experiment, the normal directions for all spatial points were properly estimated, and the correct colors of rendered materials were reproduced. Also, highlight changes on the surfaces were observed when we moved the light source or the rendered materials. It was confirmed that our system was easy to use and was able to measure the spatially-varying reflectance of real materials.