Spread Spectrum Watermark for Color Image Based on Wavelet Tree Structure

This paper proposes a spread spectrum watermark for color image based on wavelet tree structure. It embeds a pseudo-random sequence representing one bit of the original watermark into a four-fork tree in the DWT of Y component of YUV. This distributes the information of one bit into several frequency sub-bands, such as low, intermediate and high frequency sub-band, which improves the robustness of watermark against different attacks. In addition, we apply denoising method to watermark image extracted from the attacked watermarked image to remove the salt-and-pepper noise introduced by the attacks to host image, which improves the NC of watermark. Experimental results prove that the algorithm is very robust to image processing attacks such as JPEG compression, Gaussian noise, filtering, cropping and contrast enhancement, and it has a good transparency.