A Watermarking Method for Halftone Images Based on Direct Binary Search

Abstract

Watermarking techniques previously developed deal with on-line digital data. In this paper we deal with printed images rather than on-line data. Printed image watermarking is performed by exploiting the printing process itself i.e. halftoning. It hides watermark data at pseudo-random locations within a halftone image. The proposed method tries to find the best halftone image which has the least perceived halftoning error by iterative direct binary search method. The artifacts due to the inserted watermark are removed by finding the best neighborhood pixel pattern. By integrating data hiding into halftoning operation, relatively large amount of data can be hidden within a halftone image while the visual quality of final halftone image is maintained. Experimental result shows that the proposed method generates watermarked halftone images with good visual quality.