Research Of Digital Hologram Watermarking Resistant To Print-Scan Attack

With the development of information technology and the widely used of digital works, watermarking, as one of the important tools of information secrecy, is widely used in identity authentication and copyright protection. The hardcopy of digital works is often used in daily life, and watermarking technology resistanted print-scan need to be solved quickly.Already existed watermarking algorithms have a good development in performance and ability against attack. but, there still some problems, such as capacity of embedded, complexity of algorithm, the reconstruction of watermarking. The algorithm includes the following several aspects.Firstly, this section researches the change of image after print and scan in physical equipment, resolution, noise, etc, and summaries of attacks and distortion. There is two basic kinds of watermarking algorithm, one is about distortion correction, another is about find invariant feature. We introduce the traditional watermark produce methods, and proposed watermark produce method based on digital holographic.Secondly, this section researches watermarking algorithm resistant to print-scan based on discrete fourier transform (DFT). The improved algorithm is that, a hologram of two watermark is embedded into the middle amplitude spectral magnitude of the image, and the same embedded of the central semmetry block. A Peak Signal to Noise Ratio(PSNR) threshold adapted to the texture of the host image is set to adjust the watermark strength. The proposed approach shows advantages in invisibility, robustness, embedding capacity, resistance the attack of scaling, noise, JPEG compression. The watermark can be extracted from the scanned version of a printed hardcopy of the watermarked image.Finally, this section researches watermarking algorithm resistant to print-scan based on colored image. Color image watermarking algorithm is difficult to achieve because color space is changed after print-scan process. Hologram watermarking method based on discrete wavelet transform (DWT) is proposed, the watermark is embedded in the vertical component of secondary wavelet coefficients of red component. We can extraction watermark information blindly. Experimental results show that watermark can be extracted from print-scan attack.