Beyond perspective dual photography with 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 nonperspective and multiviewpoint 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 then extend this technique for multiple views by both building a virtual shadow camera array and by exploiting area sources. We also capture nonperspective 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. We demonstrate a variety of indoor and outdoor results and show a rendering application for capturing the light-field of a light-source.