Image analysis – Histogram processing – For setting a threshold
Patent
1987-07-22
1989-08-22
Boudreau, Leo H.
Image analysis
Histogram processing
For setting a threshold
356344, 358101, 382 50, G06K 900
Patent
active
048603716
ABSTRACT:
System for detecting pattern defects wherein images of corresponding portions of two originally identical patterns are detected and two image signals representing the images are registered with each other, a second image signal of the two registered signals is shifted by a predetermined number of pixels with respect to a first image signal, thus providing shifted second image signals. Differences in brightness between the first and second image signals as well as each of the shifted second image signals are calculated within intervals corresponding to pixels on one scanning line, thus providing a first group of difference image signals, preset values are added to and substracted from the first or second image signal to provide a sum image signal and a substraction image signal. Differences in brightness between the second or first image signal and each of the sum and substraction image signals are calculated within the intervals to provide a second group of at least two difference signals, normality of one of the two patterns is decided when the first group of difference signals and the second group of difference signals have coexistent positive and negative signs within one interval and a minimum of absolute values of the first group of difference signals and the second group of difference signals is calculated when the first and second group of difference signals have all either positive signs or negative signs within one interval, and the mimimum is detected as a true defect when the minimum exceeds a predetermined threshold.
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Ichinose Toshiaki
Matsuyama Yukio
Boudreau Leo H.
Hitachi , Ltd.
Mancuso Joseph
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