  Casual photography is often performed in uncontrolled lighting that can
result in low quality images and degrade the performance of downstream
processing. We consider the problem of estimating surface normal and
reflectance maps of scenes depicting people despite these conditions by
supplementing the available visible illumination with a single near infrared
(NIR) light source and camera, a so-called "dark flash image". Our method takes
as input a single color image captured under arbitrary visible lighting and a
single dark flash image captured under controlled front-lit NIR lighting at the
same viewpoint, and computes a normal map, a diffuse albedo map, and a specular
intensity map of the scene. Since ground truth normal and reflectance maps of
faces are difficult to capture, we propose a novel training technique that
combines information from two readily available and complementary sources: a
stereo depth signal and photometric shading cues. We evaluate our method over a
range of subjects and lighting conditions and describe two applications:
optimizing stereo geometry and filling the shadows in an image.
