In this paper, a novel spatial domain color image watermarking technique is proposed to rapidly and effectively protect the copyright of the color image. First, the direct current (DC) coefficient of 2D-DFT obtained in the spatial domain is discussed, and the relationship between the change of each pixel in the spatial domain and the change of the DC coefficient in the Fourier transform is proved. Then, the DC coefficient is used to embed and extract watermark in the spatial domain by the proposed quantization technique. The novelties of this paper include three points: 1) the DC coefficient of 2D-DFT is obtained in the spatial domain without of the true 2D-DFT; 2) the relationship between the change of each pixel in the image block and the change of the DC coefficient of 2D-DFT is found, and; 3) the proposed method has the short running time and strong robustness. The experimental results on two publicly available image databases (CVG-UGR and USC-SIPI) have shown that the proposed method not only has satisfied the needs of invisibility but also has better performance in terms of robustness and real-time feature, which show the proposed method has both advantages of spatial domain and frequency domain.

In this paper, an approximate Schur decomposition-based spatial domain blind color image watermarking method is proposed to protect the copyright of color images, which has low computation complexity as same as the watermarking technique in the spatial domain and strong robustness as same as the watermarking technique in the transform domain. Firstly, the approximate maximum eigenvalue of Schur decomposition is calculated in the spatial domain by the proposed method. Secondly, the approximate maximum eigenvalue is used to embed and extract the color watermark image in the spatial domain without of the true Schur decomposition. Moreover, the procedures of the proposed watermarking method are given in details. The proposed technique is performed on the spatial domain based on the approximate Schur decomposition and belongs to blind watermarking technique. Experimental results on two publicly available image databases (CVG-UGR and USC-SIPI) have demonstrated the effectiveness of the proposed method in terms of invisibility, robustness, and the real-time feature.