Viewing the hidden side of a playing card
Posted on December 15, 2015
This one of several blogs about light fields and computational photography that I am planning on writing.
The authors of the paper Dual Photography develop a technique not only capturing the a photograph from a point of view of the camera, but to computationally reverse the light rays and recreate a dual photograph from the point of view of a light source in a scene. The underlying principle is Helmholtz reciprocity and effectively switches the role of a light source and a camera.
In the figure below, a projector is used to shine light onto a scene containing a playing card and a book. The face of the card is hidden from the camera. Helmholtz reciprocity lets us use the camera to capture the scene, but then reconstruct a dual image that would be seen from the point of view of the projector, which can see the face of the card.
The following video accompanies the paper discusses this phenomenon at a high level with a number of a examples and applications. The playing card example is at roughly 4:20.
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