Methods and apparatuses for detecting classifying and measuring spot defects in an image of an object
First Claim
1. A method for detecting spot defects in an image of an object, the method comprising:
- acquiring an image of the object at only a single plane of focus;
aligning an alignment model with at least one object region within the image so as to provide at least one aligned object region;
estimating, using the image, a background image representing allowable and expected appearance within the at least one aligned object region, by using a median filter of a larger spatial scale to provide a mask for use with a median filter of a smaller spatial scale;
removing the background image from the image within the at least one aligned object region so as to provide a foreground image having at least one foreground region;
computing a threshold image for at least one of the foreground regions in the foreground image;
applying the threshold image to the foreground image within at least one of the foreground regions so as to provide a defect image; and
using connected component analysis to form candidate defects in the defect image.
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Abstract
A method is provided for detecting spot defects on an object when an allowable variation (called the “background”) in the appearance of the object can be modeled. Methods are also provided for measuring and classifying detected spot defects. An alignment model is used to align the image of the object, a background model is then used to estimate the (possibly different) background in each region, and each background is substantially removed from the image so as to form a foreground image on which blob analysis can be applied to detect spot defects, the blob analysis using a threshold image that accommodates different noise statistics for each region. The method facilitates robust spot defect inspection of fiber optic end faces, or of any object with different object regions. The method also allows use of blob analysis over a larger range of conditions, including conditions that make simple blob analysis infeasible.
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Citations
21 Claims
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1. A method for detecting spot defects in an image of an object, the method comprising:
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acquiring an image of the object at only a single plane of focus; aligning an alignment model with at least one object region within the image so as to provide at least one aligned object region; estimating, using the image, a background image representing allowable and expected appearance within the at least one aligned object region, by using a median filter of a larger spatial scale to provide a mask for use with a median filter of a smaller spatial scale; removing the background image from the image within the at least one aligned object region so as to provide a foreground image having at least one foreground region; computing a threshold image for at least one of the foreground regions in the foreground image; applying the threshold image to the foreground image within at least one of the foreground regions so as to provide a defect image; and using connected component analysis to form candidate defects in the defect image. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20)
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21. A method for detecting spot defects in an image of an object, the method comprising:
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acquiring an image of the object at only a single plane of focus; aligning an alignment model with at least one object region within the image so as to provide at least one aligned object region; estimating, using the image, a background image representing allowable and expected appearance within the at least one aligned object region; removing the background image from the image within the at least one aligned object region so as to provide a foreground image having at least one foreground region; computing a threshold image for at least one of the foreground regions in the foreground image by adding the gradient of the background image to the threshold image; applying the threshold image to the foreground image within at least one of the foreground regions so as to provide a defect image; and using connected component analysis to form candidate defects in the defect image.
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Specification