System for detecting and analyzing rounded objects

Abstract

A system is described which determines the characteristics of a substantially rounded feature, such as via hole in a printed circuit board. The system includes an image scanner for providing a serial flow of a raster scan image of pixels which represent the rounded feature. Tangent detecting circuits are further provided which select groups (i.e., neighborhoods) of pixels from the scan image, each group including pixels clustered about a plurality of chosen azimuths and adjacent to a tangent to a boundary of the rounded feature. Processing circuits are further provided to trim each selected group of pixels to eliminate pixels not lying on the tangent line. The pixels which remain after the trim operation are representative of the limits (e.g., diameter, radius, etc.) of the rounded feature and enable an analyzing circuit to determine the characteristics of the rounded feature by examining the relationships between the tangent line pixels. A second system is described which reduces the apparatus required for trimming the selected pixel groups. A tangent segment is fed into a plurality of parallel networks which initially identify right and left shoulders of the tangent segment. The identified shoulders are expanded and used as a mask on the original tangent segment to disconnect a central plateau thereof from its next lower and non-central plateaus. Subsequent trimming enables the central plateau to be identified.