Adding scale to the primal sketch

The author shows how a scale dimension can be added to Marr´s (1976) primal sketch to facilitate construction of multiscale descriptions of two-dimensional scales. In contrast to conventional scale-space approaches, this method omits any smoothing or blurring and performs grouping operations on symbolic shape tokens residing in a scale-space blackboard data structure. Two types of grouping operation are introduced: (1) fine-to-coarse aggregation of primitive-edge tokens builds coarser-scale edge maps from finer-scale information; and (2) pairwise grouping of symmetrically placed primitive edges gives rise to a primitive partial region token denoting curved-contour, primitive-corner, and bar events. The resulting collection of tokens makes the fundamental edge and region components of a shape´s geometry available to later symbolic processes, leading to shape recognition or other tasks