Deep shadows in a shallow box

We present a fast, low-cost technique to gather high-contrast 'relightable' photographs of desktop-sized objects. Instead of an elaborate light stage, we follow Mohan et al.; we place the object and a digitally-steered spotlight inside a white cardboard box, aim the spotlight at the box interior, and move the spot to light the object from N repeatable lighting directions. However, strong ambient lighting from box interreflections causes 'shallow' shadows and reduces contrasts in all basis images. We show how to remove this ambient lighting computationally from the N images, by measuring an N × N matrix of coupling factors between lighting directions using a mirrorsphere light probe. This linear method, suitable for any light stage, creates physically accurate 'deep shadow' basis images, yet imposes only a modest noise penalty, and does not require external light metering or illumination angle measurements. Results from our demonstration system support these claims.