Image fault detection system - uses optical filter in plane of spatial frequency diffraction spectrum blocking correct spectrum

摘要

A method of detecting faults in image patterns, e.g. in integrated circuit masking, uses optical filtering. It is designed to isolate statistical errors and to simplify fault detection by reducing production complexity. The spatial frequency diffraction spectrum of the image is stopped with a flat laminar amplitude filter (4) in preferred directions defined by the preferred directions of the desired image structure. Faults in the image cause light to be transmitted. Signals due to residual light which cannot normally be filtered are separated from the error signals using a threshold detector. Light detection is by television or photoelectrical methods.