A robust adaptive blind color image watermarking for resisting geometric attacks

Due to the differences of observation equipment and technical means, the size of the color digital image is not the same. In addition, most of digital watermarking methods used to protect the copyright of color digital images have weak robustness against geometric attacks. Therefore, this paper proposes a robust adaptive blind watermarking method to protect the copyright of color digital images. In the proposed method, the frequency domain characteristics of Slant transform are used to directly calculate the maximum energy coefficient of the pixel block, the maximum element of the coefficient matrix obtained after Slant transform in the spatial domain, and the color digital watermark is embedded by quantifying the maximum energy coefficient. At the same time, the adaptive strategies, which including the adaptive image size, the adaptive quantization step, the adaptive watermark encoding and the adaptive watermark embedding position, are proposed in this paper. Moreover, the proposed method can use geometric features of the image to correct many attacked images. Compared with the state-of-the-art watermarking methods, the proposed method can achieve acceptable imperceptibility and has larger watermark capacity, stronger robustness, higher security and better real-time performance.