U.S. Philips Corporation

Bastiaan J Van Donselaar

Willem D Van Amstel

An on-line method of and apparatus for inspecting an apertured mask sheet to be formed into a shadow mask for a color cathode ray tube are disclosed. In one of several embodiments described the mask sheet is linearly scanned by a laser spot transverse to the direction of advancement of the mask sheet. The peak values of the grey levels of the laser light transmitted by the mask sheet are detected and the data is convoluted electronically to form a series of convolution windows. The grey levels of the successively formed convolution windows are compared to at least one reference value and an output is produced at least in those cases where an error in the mask aperture size is detected.

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Eindhoven, Netherlands

Bastiaan J Van Donselaar