Affine structure and photometry

Motion of an observer relative to objects in a scene provides information about the structure of the scene. Changing patterns of shading due to motion relative to the light source provide information about surface structure, albedos, and light sources. One can stratify this photometric information into affine, unitary, and metric structure, much like the stratification of structure from motion. For Lambertian surfaces, if either motion or photometry give us more than affine structure, the two cues can be combined to yield full metric information. Edge constraints plus unitary photometry also give us full metric photometry. Affine structure alone contains much of the quantitative structure information, allowing us to judge such things as the ordinal relationships between the albedos