A Parallel-Hierarchical Method For Grouping Line Segments Into Contours

A highly parallel technique for linking line segments into curved contours or boundaries has been developed. This bottom-up organization of the line segments utilizes information in the line data itself and perceptual organization rules which are domain independent. The line segments can be detected on a local basis and are amenable to parallel computation.1 A line pyramid structure is employed where the two bottom levels of the pyramid hold the line segments extracted from predefined image windows (e.g. 4 x4 and 8x8). The pyramid is based on a 4 x4 overlapping neighbourhood and each processing element is connected to four parents and sixteen children. Starting from the lower level, each processing element performs grouping on the line data supplied by all of its children but it only keeps the grouped line segments supplied by its central 2x2 children for passing on to the parents. The main grouping criteria employed to achieve the aggregation of line segments are proximity, Mares theta-aggregation,2 curvilinearity, continuity and similarity in line contrast. By the time the root processor of the pyramid is reached, all the groups of line segments are formed and they are then replaced by contours. The main features of the method are its parallel implementation on a pyramid architecture computer and use of domain independent perceptual grouping principles.