A Study Of Image Digital Watermarking Technique Based On Wavelet Transform

Digital watermarking technique is a useful method to solve the problem of copyright protection and information security for multimedia content. Because wavelet transform has many predominance such as space-frequency localization, multi-resolution representation and its compatibility with the new image coding standard—JPEG2000, wavelet based watermarking techniques become the hotspot of the field, In this thesis, detailed researches are done about the image watermarking algorithms in wavelet domain. The main works and creations are as the following:1. The background and current research of digital watermarking are researched, and the basic principle of wavelet transform is studied. The basic process of watermarking algorithms in wavelet domain is introduced.2. The basic principle of error correction code is researched. An adaptive watermarking algorithm in wavelet domain is proposed and the hamming code is used to correct the wrong code. The factors which influence the digital watermark's robustness are discussed. The watermark is embedded into the low-frequency band of the wavelet image representation by changing the median value. The algorithm is safe and robust against common attacks. The quantization step is determined adaptively in accord with different images.3. A semi-blind fragile watermarking algorithm for image authentication is proposed. The problem of selection of wavelet basis is researched. Experimental results show that the proposed watermarking scheme is invisible and robust against common image processing such as JPEG compression and image enhancement. The algorithm is fragile to content modification such as blurring and adding noise and can effectively detect the tampered regions by cropping.4. A watermarking algorithm for the copyright protection of remote sensing image is proposed. The perceptually significant wavelet coefficients are selected by using human visual system and the strength of embedded watermark is determined by the just noticeable distortion. The watermark is detected hierarchically to save detection time.5. The color image watermarking algorithms are researched. The watermark's impact on image classification is studied. A military map is embedded into a color remote sensing image. The robustness of watermarking algorithms into different component of the color image is compared and analyzed. The experimental results show that the watermark embedded into the green component is robust against JPEG compression especially, while the watermark embedded into the blue component performs better when attacked by sharpening and filtering.