Dual Photography

In this talk, I will 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-reflections and caustics.

In its simplest form, the technique can be used to take photographs
without a camera. I will show results of images we captured using
only 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 reflectance field that allows
for relighting with arbitrary light fields. Since an array of cameras
can operate in parallel without interference, whereas an array of light
sources cannot, dual photography is fundamentally a more efficient way
to capture such a 6D dataset than a system based on multiple projectors
and one camera. As an example, I will describe how dual photography
can used to capture and relight scenes.
Pradeep Sen is a PhD candidate in Electrical Engineering in the Graphics
Laboratory at Stanford University. He received his BS degree in Computer
and Electrical Engineering from Purdue University in 1996 and his M.S. in
Electrical Engineering in 1998 in the area of electron-beam lithography.
He joined the Graphics Lab in the fall of 2000, and for his doctoral
thesis he developed a structure that embeds discontinuity information
in a texture in order to reduce rendering artifacts. These
"silhouette maps" can be applied to various problems in computer graphics
such as texture magnification and shadow mapping. Other publications in
graphics include work on real-time shading and dual photography. His
interests include real-time graphics and graphics hardware, global
illumination algorithms, computational photography and display technology.