Revealing Pentimenti Through Raking Angle Photography

Discovering hidden details in historical paintings, such as pentimenti, can help reveal historical influences and changing intentions of an artist. Top-down photographs of visible light historical paintings do not capture much of the finer surface detail on the object being photographed. We present a technique using only visible light photography with a specially constructed octagonal reflector to aid the discovery of hidden details in historical paintings, by measuring Fresnel reflectance effects through raking angle photography. We exploit the significantly higher reflectance of dielectric surfaces at low angles to reveal hidden details that are otherwise not visible through ordinary photography. We also present a way to explore the details both statically and interactively.