QFT-QSVD Domain Colour Image Watermarking Scheme

Watermarks can be embedded in the pixel domain or a transform domain. Discrete Fourier Transform (DFT), Discrete Cosine Transform (DCT), Discrete Wavelet Transform (DWT) and Singular Value Decomposition (SVD) have been used as mathematical tools for embedding data into an image. In this paper, we present a new robust hybrid watermarking scheme for colour images based on Quaternion Fourier Transform (QFT) and Quaternion Singular Value Decomposition (QSVD). After applying the QFT to the cover image, we map the QFT coefficients into four quadrants, and apply the QSVD to each quadrant. The singular values in each quadrant are then modified by the singular values of the QFT-transformed visual watermark. The quality of the watermarked image and extracted watermark is measured using peak signal to noise ratio (PSNR) and normalized correlation (NC) respectively. Robustness of proposed algorithm is tested for various attacks. We assume that the size of the visual watermark is one quarter of the size of the image.