基于小波系数比较的抗打印扫描数字水印算法

A digital watermarking algorithm resistive to print-scan process based on the comparison of wavelet coefficients

提出了一种在打印监控系统中应用的图像数字水印算法。将待打印的文档图像进行相同大小的分块,依据分块数量确定嵌入容量。对每一小块图像进行三级离散小波变换(DWT),通过调整子带中不同位置系数的大小关系在中频和高频分量中重复嵌入水印信息;依据择大判决原则从各子带提取的水印中确定最终水印,提取过程不需要原始图像,扫描分辨率在75dpi以上均可正确提取。实验表明,该算法能够有效抵抗几何攻击,对打印、复印和扫描具有鲁棒性,可实现对打印文件进行版权保护和来源鉴别。

The paper proposes a digital image watermarking algorithm facing printing surveillance system. Cut the original printing document image into many same size blocks, the embedding watermark quantity depends on the number of blocks, then decomposed each image by discrete wavelet transform （DWT） for three degree. We repeat embedding watermarking by comparing and modulating the coefficients that locate different positions in middle and high detail subbands; in detecting, we extracted watermarking based on maximum likelihood decision from each subband and achieve the final watermarking without original image, this algorithm can extract the watermarking exactly while the scanning resolution is above 75 dpi. Experimental results show that the algorithm is effective to resist geometry distortion and survive the print-scan process, it can achieve the purpose of copyright protection and source authentication for the printed document.