DT CWT and Schur decomposition based robust watermarking algorithm to geometric attacks

To improve the robustness of image watermarking algorithms against geometric attacks such as cropping, rotation, scaling, shearing, projective mapping, a robust image watermarking algorithm based on DT CWT and Schur decomposition is proposed. Firstly, we use Dual Tree Complex Wavelet Transform (DT CWT) to decompose the U component of the original image (cover image), the decomposed low frequency component is divided into non-overlapping N × N blocks, and Schur decomposition is applied in each block. Secondly, we modify maximum primary diagonal value of the upper triangular matrix of each block to embed the watermark. Finally, the Scale Invariant Feature Transform (SIFT) features of the watermarked image (stego-image) is saved as the SIFT key for watermark extraction. When extracting the watermark, we first use the SIFT features of stego-image and changed stego-image to obtain the geometric torsion, thereby a spatial synchronization can be guaranteed. And we then use the maximum election statistics to improve the quality of the extracted watermark. Experiment results show that the proposed algorithm can resist geometric attacks, and is more robust than the existing watermarking methods.