US Patent 10495581 Defect detection device and defect detection method

A plurality of images is acquired while changing the direction of light emission. Each captured image is compared with a corresponding reference image to acquire first dark regions from the captured image. Second light regions are acquired from the captured image. In a combination of one of a plurality of first dark region images indicating first dark regions and one of a plurality of second light region images indicating second light regions, a region of overlap between a first dark region and a second light region is acquired as a defect candidate region, and the existence of a defect is detected on the basis of the defect candidate region.