New gray-scale watermarking algorithm of color images based on Quaternion Fourier Transform

A scheme of embedding gray-scale watermark image into an RGB carrier image based on the fast Quaternion Fourier Transform (QFT) is proposed. In this algorithm, the R, G, B color components are represented respectively by the three imaginary parts of a pure imaginary quaternion. Then the gray-scale watermark image is inserted into the real part of the carrier image which is transformed by the 2D-QFT. According to the special symmetrical characteristic of the real part, the insertion of the gray-scale watermark image without lose is realized. Experiments show that the watermark inserted in the scheme has the biggest imperceptibility with the best PSNR when compared with other gray-scale watermarking schemes.