System for inspecting pad-printed characters using the normalized correlation of the segmented character images

A system has been developed for checking the quality of pad-printed characters on video cassettes using digital image processing. This system can detect blurred characters, characters with missing parts, and undesirable spots. A character is divided into several segments and the normalized correlation for each segment is calculated so that the result can be reflected by small defects and becomes similar to that of visual inspection. This special inspection algorithm has also improved the inspection speed. It takes less than 1.2 s to inspect one cassette by using five high-speed image-processing boards