A Robust Printed Image Watermarking Based on Iterative Halftoning Method

Abstract

In this paper, we propose a noble watermark embedding and extraction method for printed images. Watermark bits are hidden at pseudo-random locations within a printed halftone image during halftoning process. To remove the artifacts and distortion due to the inserted watermark bits, iterative error minimizing technique is used. During each iteration the pattern which decreases the halftone error is selected as the next pattern where the halftone error is defined as the difference of HVS-filtered printed halftone image and grayscale image. The inserted watermarks are extracted from the scanned images after a series of image processing operation which is described in detail. In order to be robust to cropping and rotation, the watermark is inserted periodically in halftone images. Experiments using real scanned images show that the proposed method is feasible method to hide the large amount of data within a halftone image without noticeable distortion and the watermark is robust to cropping and rotation.