Quaternion Image Watermarking using the Spatio-Chromatic Fourier Coefficients Analysis

In this paper, a new color watermarking algorithm that uses the quaternion fourier transform (QFT) to mark the La∗b∗ components of color images is presented. First, we propose an interpretation of the QFT coefficients using the Spatio-Chromatic Fourier analysis, so the effects of any changes to the coefficients can be predicted. Next, watermark casting is performed by modifying the positive and negative coeffi-cients together. The idea is twofold: Robustness is achieved by embedding a color watermark in the coefficient with pos-itive frequency, which spreads it to all components in the spatial domain. On the other hand, invisibility is satisfied by modifying the coefficient with negative frequency, such that the combined effects of the two are insensitive to human eyes