These departures from mere background - layout always involve an occluding edge. An edge is projected in an optic array. There are seven occluding edges in this diagram, and four corners . The converging lines do not represent rays of light but lines of sight. Compare this picture with Fig.
All occlusion is temporary occlusion.
The fact that a closed contour on a black field almost always suggests a detached object in front of a vague surface and almost always suggests an aperture or window in that surface implies only that. The specification of occlusion in a frozen optic array is less than perfect. Ambiguity may arise in certain circumstances as to object or aperture, as to cliff or overhang. The occluding edge . An occluding surface necessarily has an occluding edge which hides, covers, screens, or interposes.