Consider a small object sitting on a desk in your living room. The object is illuminated by light sources from all directions—this includes direct sources such as the sun or overhead lights, but also indirect sources, like the foliage outside that scatters sunlight through your window. The appearance of the object and the surface that it rests upon results from the complex interaction between the incident illumination and the geometry and material properties of the object and the desk. In this paper we ask the question—if the geometry and material properties of the observed scene are known, how well can we reconstruct the incident illumination pattern?
In our work we primarily make use of shadows cast by an object onto nearby surfaces. Cast shadows are particularly easy to interpret when an object is illuminated from a single direction. For example, one can immediately determine the position of the sun by looking at a sundial. Estimating the illumination incident from all directions simultaneously is more challenging, and is a linear but ill-posed inverse problem.