Digital Watermarking Algorithm Based On Wavelet Transforms

Digital watermarking technique is a leading international research field in recent years, it is an newly important branches in the information hiding technology, and also it is an effective way in copyright protections. Digital watermarking technique embeds unperceived secret information into the digital object to justify the copyright owner or to trail piratical actions.Owing to properties of total transformed ability and multiresolution analysis, digital watermarking algorithms based on wavelet transforms have currently become a well-discussed and most important research aspect.The paper studies digital watermarking models for images based on wavelet transforms, and the main contributions of this dissertation are the following:A semi-fragile watermarking algorithm based on wavelet energy is proposed: transforming images into wavelet domain, and by defining a function between the embedded watermark strength factor and the energy of the wavelet trees in wavelet domain, a new algorithm was proposed to embedded a self-adapt watermark into images. Experimental results show that the algorithm was able to detect slight changes of the watermarking images, and the detector was also sensitive to slight changes.A digital watermarking algorithm based on the wavelet transform domain was proposed: By transforming the original images into the wavelet domain, then choose the wavelet coefficients of middle layer to embed watermarking. By defining a function between the embedded watermark's strength factor and the wavelet coefficients, the paper proposed an image characteristic adaptive digital watermarking algorithm. The experimental results show that it is a high robust algorithm against JPEG compression and cropping, median filtering and noise adding.An improved JND watermarking algorithm on wavelet domain was proposed: By modifying the threshold of JND based on Human Visual System and applying the iterations of chebyshev polynomial to generate chaotic sequence as digital watermarking of images, the paper proposes a novel blind watermarking embedding and detecting algorithm, experimental results show that the algorithm has an strong robust for the usual image transforms such as median filtering, rotating, shifting, cropping, JPEG compression, noise adding, etc, especially, when the watermarked image processes all angle rotating or arbitrary shifting or cropping, the watermark can also be detected.