Image`s defects determining method, for disc-shaped object e.g. substrate, involves recording images of surface of object, and executing comparison operation when three comparison images with same image content are present in buffer store

摘要

The method involves recording individual images (20-21) of a surface of a disc-shaped object, and storing the images in a buffer store. A comparison operation is executed when three adequate comparison images with approximately same image content are present in the store, where the recording of the images proceeds parallel to the operation. The shifting of the images against each other is measured for alignment of the images.