Waltz's algorithm can be used in an inage processing pipeline after edge detection to label each edge as being either a boundary where one object partially obscures another, ora convex or concave folded edge within an object. It uses the fact that these different forms of edges have constraints where they meet; for example, two convex edges cannot normally meet at a point with a concave one. Waltz's algorithm can fail either because there is ambiguity or if here is no consistent labelling. The latter can occur with crafted images, such as those of Escher, which are locally sensible, but globally inconstent, or becasue {[uncertanty}} in lower levels of processing mean that are errors in edge detection.
Defined on page 263
Used on pages 260, 263, 266, 267, 271, 284, 285, 286
Applying Waltz's algorithm: Pass 1: Label the lines at the boundary of the scene; Pass 2: Find vertices where the currently labelled lines are sufficient to determine the type of the vertex; Pass 3: Label the rest of the lines from those vertices accordingly.