Robust periodic blind watermarking based on sub-block mapping and block encryption.

Digital watermarking is of critical importance in multimedia copyright protection. However, with the development of Internet technologies, the combined attacks of complex environments challenge to the robustness of traditional digital watermarking schemes. In order to tackle this problem, a robust periodic blind watermarking scheme based on sub-block mapping and block encryption is proposed in this paper to enhance robustness under combined attacks. Concretely, a watermark is encoded by the periodic encoding method to raise the fault tolerance rate. Then a block encryption technique is designed to encrypt periodic sub-blocks by utilizing different encoding methods to maintain the security of copyright information. To achieve high image quality, this scheme employs a sub-block mapping mechanism to map the encrypted periodic watermark into a smaller watermark to minimize the visual difference between host image and watermarked image. Finally, an improved Singular Value Decomposition (SVD) is conducted to embed a quaternary watermark that can extend to a gray-scale watermark. Experimental results demonstrate that the proposed watermarking scheme has good visual quality of watermarked images and is robust to image processing attacks, especially in cropping, scaling and combined attacks, which is better than other watermarking schemes. [ABSTRACT FROM AUTHOR]