Patent ID: 7415150
Filing Date: 2008-08-19
Classification: G03F,G06T

Abstract:
1. A method for computing translational differentials between a database-image and a scanned-image of a photomask, the method comprising: receiving a noise-free database-image and a scanned-image that is generated by an imaging process; computing a set of candidate-translational-differentials using the database-image and the scanned-image; generating one or more sets of translated directional-gradient-images based on the set of candidate-translational-differentials and using the database-image and the scanned-image; converting the database-image into a set of smoothed directional-gradient-images; and computing translational differentials by performing a normalized correlation using the set of smoothed directional-gradient-images and the one or more sets of translated directional-gradient-images; wherein the computational time is significantly reduced because the method performs normalized correlation using the set of candidate-translational-differentials, instead of exhaustively performing normalized correlation using all possible translational differentials.