Research On Robust And Semi-fragile Watermarking Algorithms For Digital Image Based On DWT

With the great development of multimedia technology and the popularity of Internet, distributing of digital products through Internet is more and more convenient. Meanwhile, the problem of multimedia copyright protection becomes increasingly serious. In recent years, robust and semi-fragile digital watermarking techniques become significant solutions to copyright protection. After analyzing the existing watermarking algorithms, a robust digital watermarking system and a semi-fragile digital watermarking system based on DWT and HVS are proposed. When subject to various attacks algorithms, the performance of them is good.In terms of robust digital watermarking, the embedding and detecting algorithms are analyzed sufficiently. First, the watermark is srambled by means of Zigzag transformation, and is pre-processed by means of Spread Spectrum. After those processing, a safe watermark sequence is acquired. Second, based on the characters of HVS, the watermark sequence is embedded into LL2 component of the two-stage DWT, which shows good robustness when attacked by various algorithms such as adding noise, quantification, and geometric attacks.In terms of semi-fragile digital watermarking, the embedding and authenticating algorithms are analyzed profoundly. A semi-fragile digital watermarking algorithm based on DWT is proposed. By means of the characteristics of HVS and DWT, the watermark signals are embedded into HL2, LH2, HH2 of the three-stage DWT, which shows good performance in the aspect of perceptive transparency of the watermark signals and authentication of the host picture.In the end, the proposed semi-fragile watermarking is analyzed compared with the typical semi-fragile watermarking in the aspect of detection of tamper, security, reliability, imperceptions. Theoretical analysis and experimental result show that the proposed algorithm is effectively resistance to counterfeiting attack, and also keep sharp partial tamper detecting. So it's a safe, effective and reliable semi-fragile watermarking algorithm.