Surface defect inspection system and method

A system for detecting defects on a coated surface, the system comprising:

• a source of diffuse light arranged for emitting an elongated line of light having a leading edge and a trailing edge onto a moving substrate having a direction of travel substantially perpendicular to said line of light such that said substrate passes therethrough, a workpiece to be inspected being supported by said moving substrate;
• an area detector for viewing said substrate and capturing images of the received light scattered by a surface of said workpiece, said detector being operative to view a portion of the surface of the workpiece including that illuminated by said line of light, said detector having a frequency of operation selected so that each portion of the surface of said workpiece is imaged at least twice during said workpiece's traversal through the field of view of the detector;
• means for generating digital signals, including first and second sets of digital signals corresponding to the amplitude of scattered light received by said detector during said two captured images of a portion of said workpiece;
• and
• means for comparing said first and second sets of digital signals to isolate and amplify variations in the amplitude of received light caused by a defect in said workpiece surface, wherein the means for comparing said first and second sets of digital signals includes substracting first and second sets of digital signals one from the other to form a composite set of digital signals and applying a finite impulse response filter to the composite set of digital signals such that the filter is designed to detect correlation in accordance with the speed of the workpiece and the time between the two captures images.