基于光学菲涅耳衍射,设计了一种新的“盲数字水印”计算方法。水印图像通过离散菲涅耳衍射变换成一复矩阵,将此复矩阵的实部和虚部分开,分别嵌入到宿主图像的不同位置中。通过将水印嵌入点的宿主图像的像素值更改为其近邻像素值的均值,而实现“盲水印”的提取。数值计算结果表明:该水印计算法对像素变换攻击具有很强的鲁棒性,如图像亮度、对比度和灰度曲线的调整;能抵抗JPEG有损压缩、剪切和噪声污染攻击;能抵抗对图像的重采样攻击,可从显示屏幕拷贝的图像中提取水印。由于该方法为使用者提供了灵活的水印嵌入方式和双重密钥的选取,以及提取水印不需要原始图像数据,因而使该方法具有很高的安全性和实用价值。

A new blind digital watermarking algorithm based on optical Fresnel diffraction is proposed. The watermarking image is transformed into a complex matrix after discrete Fresnel diffraction. The complex matrix is separated into real and imaginary parts, which are embedded into the host image for different positions, respectively. The blind watermark is obtained by replacing the value of the embedded pixel of the original host image with the average of adjacent pixels. Numerical calculation shows that the algorithm is robust to the attack of the pixel modifications, such as brightness, contrast and gray curve, and has the resistance to the JPEG lossy compressing, cropping and superposing noise. It's also robust to the resampling attack and can be drawed from the image by the screen copy. Because the watermark can be embedded in the image flexibly, the double keys are designed in the large degrees of freedom, and the watermark can be retrieved from the published image without the original image, the algorithm has high security and practical value.