Color image watermarking using local quaternion Fourier spectral analysis

We propose a watermarking scheme for color images based on local quaternion Fourier spectral analysis (LQFSA).The merits of the proposed scheme include: 1) Quaternion Fourier transform is defined in a 4D vector space and thus provides a larger embedding scope for watermark than conventional monochannel transformation techniques. 2) We improve the imperceptibility of watermark with regard to human color vision properties through LQFSA. 3) We introduce invariant feature transform (IFT) and geometric correction scheme so as to enhance the robustness to extensive attacks, which is another essential factor to evaluate a watermarking scheme. 4) We adopt the nearest-neighborhood search to ensure the correctness of watermark extraction. Extensive experiments on the Stirmark platform validate the aforementioned merits.