Coherence as Texture - Passive Textureless 3D Reconstruction by Self-Interference

Passive depth estimation based on stereo or defocus relies on the presence of the texture on an object to resolve its depth. Hence, recovering the depth of a textureless objectfor example, a large white wall-is not just hard but perhaps even impossible. Or is it? We show that spatial coherence, a property of natural light sources, can be used to resolve the depth of a scene point even when it is textureless. Our approach relies on the idea that natural light scattered off a scene point is locally coherent with itself, while incoherent with the light scattered from other surface points; we use this insight to design an optical setup that uses selfinterference as a texture feature for estimating depth. Our lab prototype is capable of resolving depths of textureless objects in sunlight as well as indoor lights.