Turning Corners into Cameras:         

Principles and Methods

Katherine L. Bouman,       Vickie Ye,      Adam B. Yedidia,      Fredo Durand,
     Gregory W. Wornell       Antonio Torralba       William T. Freeman

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We construct a 1-D video of an obscured scene using RGB video taken with a consumer camera. The stylized diagram in (a) shows a typical scenario: two people—one wearing red and the other blue—are hidden from the camera’s view by a wall. Only the region shaded in yellow is visible to the camera. To an observer walking around the occluding edge (along the magenta arrow), light from different parts of the hidden scene becomes visible at different angles (see sequence (b)). Ultimately, this scene information is captured in the intensity and color of light reflected from the corresponding patch of ground near the corner. Although these subtle irradiance variations are invisible to the naked eye (c), they can be extracted and interpreted from a camera position from which the entire obscured scene is hidden from view. Image (d) visualizes these subtle variations in the highlighted corner region. We use temporal frames of these radiance variations on the ground to construct a 1-D video of motion evolution in the hidden scene. Specifically, (e) shows the trajectories over time that specify the angular position of hidden red and blue subjects illuminated by a diffuse light.

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.

In the News

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Acknowledgements

This work was supported in part by the DARPA REVEAL Program under Contract No. HR0011- 16-C-0030, NSF Grant 1212849, Shell Research, and an NDSEG Fellowship (to ABY). We thank Yoav Schechner, Jeff Shapiro, Franco Wang, and Vivek Goyal for helpful discussions.