Robust Watermark Model Based on Subliminal Channel

Current watermark models cannot reflect the conflicting relationship among cover fidelity, watermark robustness and watermark capacity. And there is no effective guidance for designing robust watermark algorithms in content security applications, such as the copyright protection. A robust watermark model based on subliminal channel for content security applications is proposed. In this model, the half- symmetry of watermark communication is pointed out. Based on the model, the approaches to solve the conflicting relationship are presented as to increase entropy of cover, to decrease entropy of watermark message and to increase mutual information between cover and watermark through cover transformation, watermark encoding, public and subliminal channel encoding. The conditions and methods of the cover transformation and watermark encoding are presented. This model and its approaches will offer theory guidance for researches on robust watermark algorithms in content security applications.