Patent ID: 7796248

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: 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; determining, based on a contrast of an image of a defect candidate obtained by the search, whether a real image or a virtual image was formed; and determining, based on an appearance pattern of the real image or the virtual image, whether the defect candidate is located on the main surface, inside, or on the rear surface of the transparent plate material.