Method of and apparatus for inspecting transparent object for defect

摘要

In a method of and an apparatus for inspecting a transparent object for a defect wherein the presence or absence, and the shape and kind of a defect can be detected accurately, a pitch of stripes (7, 8) of a reference pattern (1a) is detected first. Then, an inspection object (4) is placed in position, and light of the reference pattern is projected upon the object to photograph transmission light by an image sensor (11). A threshold value (UTH, LTH) is set from an average value between two picture element data spaced from each other by one half (P/2) the detected pitch (P). The picture element data are successively compared with the threshold value to determine the bright or the dark thereof. A defect (9) of the object is discriminated from numbers of thus determined bright and dark picture elements.