Digital watermarking based on color differences

In this paper, we proposed the digital watermarking for a color image. In order to embed watermark signal, we consider the characteristics of HVS(human visual system) and focus on the relatively insensitive components of a color image. In YCrCb color space, Y component is achromatic luminance and both Cr and Cb components are chromatic color. At the Cr-Cb chrominance plane, an angle of a pixel represents the hue component of a color that refers to its average spectral wavelength and differentiates different colors and a magnitude of a pixel determines the amount of purity of the color. Because the variation of saturation is less sensitive than that of hue, we modify the saturation value the magnitude in Cr-Cb chrominance plane. On changing the chrominance data, the phase of a point has to be fixed and only the magnitude of the point that represents the saturation is changed based on the acceptable degree of color difference. The proposed digital watermarking method has a good property in the field of invisibility.