| 摘要 |
A front side surface of a cover glass of a solid state imaging device is focused, and a front side image is captured. Next, a rear side surface of the cover glass is focused, and a rear side image is captured. The front side image and the rear side image are combined with each other to create a composite image. A first threshold value is set for each pixel in the composite image by dynamic thresholding. An image composed of pixels whose gray values exceed the first threshold value is identified as a defect candidate image. The maximum gray value of the defect candidate image is multiplied by a constant rate to set a second threshold value. An image composed of pixels whose gray value is less than the second threshold value is eliminated as a blurred image from the defect candidate image. Thereby, only a spot defect image, an allowable defect image, and a stain defect image remain in the composite image.
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