This thesis presents novel research work on copyright protection of grey scale and colour digital images. New blind frequency domain watermarking algorithms using one dimensional and two dimensional Walsh coding were developed. Handwritten signatures and mobile phone numbers were used in this project as watermarks. In this research eight algorithms were developed based on the DCT using 1D and 2D Walsh coding. These algorithms used the low frequency coefficients of the 8 × 8 DCT blocks for embedding. A shuffle process was used in the watermarking algorithms to increase the robustness against the cropping attacks. All algorithms are blind since they do not require the original image. All algorithms caused minimum distortion to the host images and the watermarking is invisible. The watermark is embedded in the green channel of the RGB colour images. The Walsh coded watermark is inserted several times by using the shuffling process to improve its robustness. The effect of changing the Walsh lengths and the scaling strength of the watermark on the robustness and image quality were studied. All algorithms are examined by using several grey scale and colour images of sizes 512 × 512. The fidelity of the images was assessed by using the peak signal to noise ratio (PSNR), the structural similarity index measure (SSIM), normalized correlation (NC) and StirMark benchmark tools. The new algorithms were tested on several grey scale and colour images of different sizes. Evaluation techniques using several tools with different scaling factors have been considered in the thesis to assess the algorithms. Comparisons carried out against other methods of embedding without coding have shown the superiority of the algorithms. The results have shown that use of 1D and 2D Walsh coding with DCT Blocks offers significant improvement in the robustness against JPEG compression and some other image processing operations compared to the method of embedding without coding. The originality of the schemes enables them to achieve significant robustness compared to conventional non-coded watermarking methods. The new algorithms offer an optimal trade-off between perceptual distortion caused by embedding and robustness against certain attacks. The new techniques could offer significant advantages to the digital watermark field and provide additional benefits to the copyright protection industry.
|Date of Award||31 Dec 2013|
- The University of Manchester
|Supervisor||Patrick Gaydecki (Supervisor)|
- Discrete cosine transforms (DCT), watermarking, Walsh coding, grey image, Zena colour image