在Contourlet域中,结合计算全息技术提出一种基于计算全息的强鲁棒性自适应水印算法.将两个原始水印图像利用共轭对称延拓傅立叶计算全息分别生成对应的全息水印,并利用预处理方法对全息水印进行加密处理.将原始图像进行2级Contourlet变换,得到的中频信息进行8方向分解,得到8个方向子带.利用Contourlet变换的多方向性和各向异性,将两幅加密全息水印自适应地替换中频的两个方向子带,实现水印的嵌入.实验结果表明,含水印图像与原始图像的PSNR值为38385 7 dB,水印隐蔽性好.在JPEG压缩因子为30的情况下,提取的水印信息清晰.当剪切含水印图像30%时,提取出的水印信息依然清晰可辨认.对噪声和低通滤波攻击均有很强的抵抗能力,并且可以有效抵抗打印扫描攻击.在水印提取时,不需要原始图像.本文提出的数字水印算法可以广泛应用在数字图像和印刷图像的版权保护中.

An adaptive watermarking algorithm based on computer generated holography with strong robustness is proposed.Firstly,two original watermarks are converted to holograms using the computer generated holography by the conjugate-symmetric extension.And the holograms are encrypted by the pre-process method.Then,the original image is decomposed into two pyramidal levels by Contourlet transform,and the intermediate frequency is transformed into eight directional subbands.Finally,encrypted holograms are embedded into the directional subbands adaptively.Experiments demonstrate that the PSNR of watermarked image is 38385 7 dB.The extracted watermarks can be well recognized when JPEG compression quality factor is bigger than 30 and cropping part is less than 30%.The proposed method also can well resist attacks such as Gaussian noise,salt & pepper noise,speckle noise,Gaussian filtering,median filtering and average filtering.And the watermarks extracted from print-scan experiment can be well recognized.In the phase of watermark extraction,original image is not needed.The watermarking technology proposed can be widely used in copyright protection of digital and printed images.