A robust image watermarking scheme based on image normalization and contourlet transform

It is a challenging work to solve the geometric attack in the field of digital watermarking. In order to solve the synchronization between the host image and the watermark, image normalization is introduced. Firstly, the geometrically invariant space of image is constructed by using image normalization, and a region of interest (ROI) is obtained from the normalized image by utilizing the invariant centroid theory. Then, the contourlet transform is performed on the ROI. Low-pass sub-band coefficients are divided into non-overlapping blocks. Finally, as the energy of the blocks are not the same, an adaptive quantization step is used to embed the binary watermark information on the maximum singular value of the block. The experimental results demonstrate that the watermarked images exhibit high visual quality, and the scheme is effective against common image processing and geometric distortions.