Imaging Behind Occluders Using Two-Bounce Light

We introduce the new non-line-of-sight imaging problem of imaging behind an occluder. The behind-an-occluder problem can be solved if the hidden space is flanked by opposing visible surfaces. We illuminate one surface and observe light that scatters off of the opposing surface after traveling through the hidden space. Hidden objects attenuate light that passes through the hidden space, leaving an observable signature that can be used to reconstruct their shape. Our method uses a simple capture setup—we use an eye-safe laser pointer as a light source and off-the-shelf RGB or RGB-D cameras to estimate the geometry of relay surfaces and observe two-bounce light. We analyze the photometric and geometric challenges of this new imaging problem, and develop a robust method that produces high-quality 3D reconstructions in uncontrolled settings where relay surfaces may be non-planar.