Pattern alignment generator

The invention concerns apparatus for comparing two patterns translated into electronic data streams, one pattern being a Reference Pattern with which the other pattern, referred to as an Inspection Pattern, is to be compared. The apparatus comprises means for reading each of the patterns pixel and includes first comparison means (90) for comparing a Reference Pattern pixel with a plurality of adjacent pixels in the Reference Pattern to determine the presence or absence of edges, means (80) for comparing pixels of the Reference Pattern with nominally corresponding pixels of the Inspection Pattern to determine whether or not the pixels are the same, and alignment means (81) for automatically incrementing or decrementing the coordinates of the pixels of the Inspection Pattern to compensate for discrepancies between edges in the Reference Pattern and nominally corresponding edges in the Inspection Pattern thereby to bring the two patterns into effective alignment.