1. A method of checking bit-map representations of an article for compliance with preselected geometrical constraints, said method comprising: feeding said bit-map in a raster scan line format to an input of a pipeline of serial neighborhood transformation stages; performing a series of neighborhood transformations in said pipeline to detect regions in the bit-map not complying with said geometrical constraints; and generating a transformed bit map at the output of the pipeline flagging said detected regions in noncompliance.