Lab meeitng 22 Sep., 2006 (Eric): Dual Photography

Authors: Pradeep Sen, Billy Chen, Gaurav Garg, Stephen R. Marschner, Mark Horowitz, Marc Levoy, Hendrik P. A. Lensch

From: ACM SIGGRAPH 2005 conference proceedings

Abstract: We present a novel photographic technique called dual photography,
which exploits Helmholtz reciprocity to interchange the lights
and cameras in a scene. With a video projector providing structured
illumination, reciprocity permits us to generate pictures from
the viewpoint of the projector, even though no camera was present
at that location. The technique is completely image-based, requiring
no knowledge of scene geometry or surface properties, and
by its nature automatically includes all transport paths, including
shadows, inter-refections and caustics. In its simplest form, the
technique can be used to take photographs without a camera; we
demonstrate this by capturing a photograph using a projector and
a photo-resistor. If the photo-resistor is replaced by a camera, we
can produce a 4D dataset that allows for relighting with 2D incident
illumination. Using an array of cameras we can produce a 6D
slice of the 8D re-refectance feld that allows for relighting with arbitrary
light felds. Since an array of cameras can operate in parallel
without interference, whereas an array of light sources cannot, dual
photography is fundamentally a more effcient way to capture such
a 6D dataset than a system based on multiple projectors and one
camera. As an example, we show how dual photography can be
used to capture and relight scenes.

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