Goniophotometric System for Measuring Object Surface Reflection Using Robot Arms

This paper proposes a goniophotometric system for measuring light reflection on an object surface using two commercial robot arms and a digital camera. It allows four degrees of freedom in incident and viewing angles necessary for full parametrization of a reflection model. Collected images are transformed as if they were all captured from the same viewing direction. A database of measured surface reflection is then constructed directly from the pixel values of the transformed images at each individual point on the object surface for a whole set of incident and viewing angles. From the collected image database, the parameters for the Torrance-Sparrow surface reflection model, such as diffuse reflectance, specular reflectance and surface roughness, are estimated. The proposed system enables two-dimensional pixel-wise measurement and modeling of surface reflectance, and thus, can deal with objects with spatially nonuniform surface reflectance. Experiments were performed on colored polyvinyl chloride sheets. The estimated Torrance-sparrow reflection models showed good agreement with the measurement data obtained by the proposed system.