Image Understanding

3.3Shape from Shading

In contrast to the techniques in photometric stereo and structure from motion that need to at least capture two images of a scene, the technique of shape from shading can recover the shape information of a 3-D scene from a single image.

3.3.1Shading and Shape

When an object is illuminated in a scene, different parts of its surface will appear with different brightness, as they are oriented differently. This spatial variation of brightness is referred to as shading. The shading on an image depends on four factors: The geometry of the visible surface (surface normal), the radiance direction and radiance energy, the relative orientation and distance between an object and an observer, and the reflectance property of the object ...