基于叠层衍射的数字水印算法研究

基于叠层衍射成像原理提出了一种新的衍射数字水印算法:叠层水印. 通过双随机相位编码和探针, 实现对水印图像的分块加密, 密文经过衰减处理, 加载在振幅型宿主图像的空域上, 伪探针记录下宿主图像, 并加载到传输图像的相位上. 模拟实验结果表明: 首先, 叠层水印可以很好地提取水印图像的振幅、相位信息. 其次, 叠层水印可以解决水印不可感知性与密文信息提取质量之间的矛盾. 最后, 通过鲁棒性研究验证了: 叠层水印具有很好的抗噪声和抗剪切能力, 并且可以通过增加探针的数目和交叠率进一步提高其鲁棒性, 并给出其在GIF图像上的应用.

Watermarking algorithm based on ptychographical imaging

We propose a method for watermarking algorithm using ptychographical imaging. The proposed method uses four probes and one fake probe for illumination, orderly. And five weighted double phase-encoded hidden images are added to a host image that is referred to as the transmitted image. Specifically, the amplitude of the transmitted image contains encoded and attenuated watermark image. And the phase of the transmitted image is the host image due to the application of the fake probe. We develop an analytical presentation for the experimental principle using mathematical derivation of the fake probe and ptychographical imaging. We test analytically the distortion of the transmitted image that is due to noise jamming and the effect of the occlusion of the pixels of the transmitted image. Moreover, we discuss the impact of the probe number and probe overlap rate on system robustness, respectively. Results of computer simulations are presented. First, the amplitude and phase of the watermark image are extracted well. Second, the contradiction between watermark imperceptible and watermark extraction quality can be resolved. Third, the simulations illustrate the system ability to extract the watermark image under distortions and the robustness of the transmitted image against removal trials. Furthermore, the robustness of the system is improved, as the number or overlap rate of the probe increases. In the end, the proposed method is applied to GIF images.