Relief articulation techniques

We consider techniques used in the articulation of pictorial relief. The related "cue" best known to vision science is "shading". It is discussed in terms of an inverse optics algorithm known as "shape from shading". However, the familiar techniques of the visual arts count many alternative cues for the articulation of pictorial relief. From an art technical perspective these cues are well known. Although serving a similar purpose as shading proper, they allow a much flatter value scale, making it easier to retain the picture plane, or major tonal areas. Vision research has generally ignored such methods, possibly because they lack an obvious basis in ecological optics. We attempt to rate the power of various techniques on a common "shading scale". We find that naive observers spontaneously use a variety of cues, and that several of these easily equal, or beat, conventional shading. This is of some conceptual interest to vision science, because shading has a generally acknowledged ecological basis, whereas the alternative methods lack this.