Turning Corners into Cameras: Principles and Methods

Abstract:

We show that walls, and other obstructions with edges, can be exploited as naturally-occurring “cameras” that reveal the hidden scenes beyond them. In particular, we demonstrate methods for using the subtle spatio-temporal radiance variations that arise on the ground at the base of a wall’s edge to construct a one-dimensional video of the hidden scene behind the wall. The resulting technique can be used for a variety of applications in diverse physical settings. From standard RGB video recordings, we use edge cameras to recover 1-D videos that reveal the number and trajectories of people moving in an occluded scene. We further show that adjacent wall edges, such as those that arise in the case of an open doorway, yield a stereo camera from which the 2-D location of hidden, moving objects can be recovered. We demonstrate our technique in a number of indoor and outdoor environments involving varied floor surfaces and illumination conditions.

Interesting. I realised a few years ago that I automatically look down any time I approach a blind corner (when walking through an office, for example). Once I noticed it took me a while longer to figure out that I was looking for the subtle diffuse shadowing that means you're about to walk into someone.

video: https://www.youtube.com/watch?v=p5_tpq5ejFQ

page: http://graphics.stanford.edu/papers/dual_photography/