Improvement of watermark detection ability based on blockwise image compensation for geometrical distortions

One of the important problems of watermarking techniques is the weakness against geometrical distortions because of synchronization loss. In this paper, we propose an image compensation scheme against geometrical distortions in order to extract watermarks correctly. Our scheme collects the feature points in an image so as to recover the distortions caused by geometrical distortion attacks. Such feature points are selected by the local maximal value of partitioned regions which can be obtained by several filtering operations. Based on the computer simulated results, we have searched the optimal filtering operation and interpolation, and then studied the validity of our scheme. (c) 2006 Wiley Periodicals, Inc.