提出一种新的基于信息光学的数字水印方法。该方法将水印信息隐藏于半色调编码的计算全息图之中。通过相位复原技术将需隐藏的水印信息编码为相位函数嵌入在复波前中,其振幅定义为宿主图像,通过计算全息记录复波前并对全息图进行半色调编码完成水印信息的嵌入。水印的提取过程只需对含有水印信息的半色调图像进行光学或数字的傅里叶变换即可完成。并给出了算法有效性的理论分析和仿真实验结果。结果证明这种水印技术对于各种数字图像处理操作具有很高的稳健性,且半色调编码图的二值特性使嵌入水印具有很强的抗打印、抗复印、抗扫描的能力。

A new approach of digital watermark based on information optics is presented. The watermark information is hidden in a halftone encoded computer-generated hologram. The watermark is encoded as a phase function of wave front by means of phase retrieval technique while the host information is taken as the amplitude of wavefront. Furthermore, the encoded wavefront is recorded through the computer generated hologram, and followed by a halftone encoding to achieve the watermark embedding process. The watermark can be retrieved by using either optical or digital Fourier transform on halftone images containing the watermarked information. The simulation results are presented and show good agreement with theoretical analysis. It is shown that the proposed watermarking technique is robust to various image processing operations. The binary characteristic of halftone encoded image grants the embedded watermark the ability to resist printing, hardcopy and scanning.