Digital Watermarking Algorithms Based On Threshold-Adjustment For Halftone Images

In many printing and publishing applications, it is desirable to embed data in halftone images for copyright and authentication purposes. So, it is significant to take more efforts to work over halftone digital watermarking different from regular digital watermarking.The key question to research halftone digital watermarking is hiding information in halftone images of limited information entropy through forming rules, which ensures the vision effect of halftone images and embedding capability of watermarking at the same time. Mainly aiming at the deficiency of embedding capability and the dissatisfying vision effect of watermarking halftone image at particular conditions of two existing halftone digital watermarking algorithms, this paper adds digital Scramble to increase vision effect and watermarking embedding capability, uses chaos digital sequence in the process of watermarking embedding halftone, encrypts the halftone digital watermarking to ensure the security of watermarking. Finally, the paper proposes a new threshold adjustment strategy to resolve the disadvantages of the two algorithms, which uses a smaller threshold adjustment matrix, human vision system being considered, halftone quality and watermarking embedding capability taken into account also.Through the quality measurement method based on human vision system, it is proved that the new proposed algorithm in the paper greatly improves the vision effect, increases the capability distinctly through watermarking image anti-noise tests, improves greatly the security is due to the watermarking encrypting. Moreover, it can be used on more than ten regular error diffusion halftone cores generally.