Coherence As Texture – Passive Textureless 3D Reconstruction by Self-interference

Passive depth estimation based on stereo, defocus, or shading relies on the presence of the texture on an object to resolve its depth. Hence, recovering the depth of a textureless object---for 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 light scattered off a scene point is fully coherent with itself, while incoherent with others; we use this insight to design an optical setup that uses self-interference as a criterion for estimating depth. Our lab prototype is capable of resolving depths of textureless objects in sunlight as well as indoor lights.