Shadow cameras: Reciprocal views from illumination masks

Scene appearance from the point of view of a light source is called a reciprocal or dual view. Since there exists a large diversity in illumination, these virtual views may be non-perspective and multi-viewpoint in nature. In this paper, we demonstrate the use of occluding masks to recover these dual views, which we term shadow cameras. We first show how to render a single reciprocal scene view by swapping the camera and light source positions. We extend this technique for multiple views by building a virtual shadow camera array with static masks and a moving source. We also capture non-perspective views such as orthographic, cross-slit and a pushbroom variant, while introducing novel applications such as converting between camera projections and removing refractive and catadioptric distortions. Finally, since a shadow camera is artificial, we can manipulate any of its intrinsic parameters, such as camera skew, to create perspective distortions.