A combined domain watermarking algorithm of color image

At present, some watermarking techniques have been proposed to protect the copyright of image either in frequency domain or in spatial domain. Designing a combined-domain watermarking algorithm is a difficult problem, which not only has short running time of spatial-domain watermarking algorithm but also has strong robustness of transform-domain watermarking algorithm. In this paper, a novel color image watermarking algorithm in spatial domain combining the principle of discrete Wavelet transform (DWT) is presented to embed color watermark image into color carrier image. At first, how to get the first low-frequency coefficient of DWT in spatial domain is analyzed. Then, the changing quantity of the first low-frequency coefficient in spatial domain is calculated by the presented algorithm. According to the presented features of the first low-frequency coefficient, the processes of embedding watermark and extracting watermark information are finished in spatial-domain instead of DWT. This presented algorithm has the following two innovations: (i) the first low-frequency coefficient of DWT is computed by image pixels in spatial domain; (ii) the presented algorithm is as robust as the transform-domain watermarking methods, and it is as rapid as the spatial-domain watermarking methods. The simulation data shows the presented algorithm has good watermarking performances as respect to visual imperceptibility, robustness, payload, and running time.