基于扩频调制和视觉掩蔽的彩色图像盲水印算法

为了更好地实现彩色图像的版权保护，首先，从理论上说明了应该选择彩色图像绿色分量嵌入水印，然后提出了一种新的适应彩色图像的盲水印算法。该算法先对宿主图像的绿色分量以8×8pixels分块进行DCT变换；然后将二值水印图像用两个互不相关的伪随机序列进行扩频调制；最后为了最大限度地增强水印强度，且不影响透明性，通过引入人眼视觉掩蔽因子，将调制好的水印根据视觉掩蔽因子大小，不同强度地嵌入到DCT变换域的中频子带系数上。该算法是通过比较两个伪随机序列和水印化图像的相关性大小来提取水印，不需要原始图像的参与，为盲水印算法。实验结果证明，该算法能有效抵抗JPEG压缩、加噪、剪切、滤波等常见攻击,而且在绿色分量中嵌入水印比在红色和蓝色分量中嵌入水印能更好地抵抗JPEG压缩的攻击。

Color Image Blind Watermark Algorithm Based on Spread Spectrum Modulation and Visual Masking

In order to better protect the copyright of the color image, this paper explained theoretically why the green color image component should be chosen to embed into a watermark, and thus proposed a new blind watermark algorithm for a color image. First, the green component of the original image was divided block by block with size 8×8 pixels, and transformed with discrete cosine transformation (DCT). Second, the binary watermark image was spread spectrum modulated by two uncorrelated random sequences. At last, in order to maximize the enhanced watermark strength without affecting transparency, human visual masking factor was imported. And the modulated watermark with different intensities was embedded in mid-frequency region coefficients of DCT domain based on visual masking factor magnitude. The watermark was extracted by comparing the relativity between two random sequences with watermarked image, and the process did not need the original image, which means a blind watermark algorithm. Experimental results demonstrated that this method was invisible and robust against some usual attacks such as JPEG compression, cropping, adding noise, and embedding watermark in a green component is more robust against lossy compression than embedding watermark in a red or blue component.