Patent ID: 7420671

Claim:
A defect inspection method for a transparent plate material for detecting a bubble, a scratch, a foreign matter, and another defect existing on or in the transparent plate material, the method comprising the steps of: capturing a first image of a main surface of the transparent plate material by using a first reflective bright-field optical system disposed at a main surface side of the transparent plate material, the first optical system comprising a first linear light source and a first camera; capturing a second image of a rear surface of the transparent plate material by using a second reflective bright-field optical system disposed at a rear surface side of the transparent plate material, the second optical system comprising a second linear light source and a second camera; searching for a defect candidate in each of the first and second images; checking, based on a result of the search, whether the defect candidate is located at positions corresponding to each other in the first and second images; regarding the defect candidate as a defect, when the defect candidate is located in both the first and second images; and regarding the defect candidate as a pseudo defect, when the defect candidate is located in only one of the first and second images.