In an image of a scene illuminated by a single source, such as a landscape in sun light, the light field is approximately the same at all locations in the scene. This is apparent from the common direction of cast shadows, the common polarity of illuminated and shaded parts of convex objects, and so forth. Here we concentrate upon the statistics of texture due to 3D surface corrugations. We show that patches of roughly uniform texture reveal the local direction of the illumination. In this way we are able to map the global structure of the "illuminance flow" through simple image processing techniques. We propose a theoretical treatment of texture due to illuminaton of rough surfaces and we present experiments on real textures and scenes. The illuminance flow is a robust indicator of the light field and thus reveals global structure in a scene. It is an important entity for many subsequent inferences from the image such as shape from shading.
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