Method of and apparatus for comparing data signals in an electrooptical inspection system
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United States of America Patent
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Jul 26, 1988
Grant Date -
N/A
app pub date -
Jun 4, 1987
filing date -
Jun 4, 1987
priority date (Note) -
Expired
status (Latency Note)
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Abstract
A system of detecting abrupt optical deviations in an object such as defects in a TV tube faceplate employing a line scan camera operated at a fixed scan frequency to feed analog video signals to a log amplifier the output of which is high-pass filtered to detect on an illumination invariant basis defect indicating deviations in light emanating from the object. The passed logarithmic deviation signals are compared with threshold signal magnitudes predetermined for the areas of the object from which the deviation signals are induced and if equal to the threshold an event signal is issued. The absolute magnitude of the event is measured by high pass filtering the analog video signal so that only the abrupt deviation from background light intensity is passed to a memory enable by the event signal. In defect analysis the size of the defect is measured as a pixel count of those pixels having signals exceeding one half the maximum pixel signal magnitude within the defect.
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