针对线状光栅仅适用于调幅图像的属性,研究了基于调频图像为载体的相位调制潜像防伪技术。采用相位调制法将潜像隐藏在误差扩散加网图像上,将图像互信息值作为隐藏效果的评价指标;基于光栅提取原理,设计一种不规则光栅;基于不规则光栅的设计理念,探究其在调幅图像上的适用范围。实验结果表明:不规则光栅能清晰地提取调频图像中的潜像,还可用于调幅图像的不同阶调。该研究实现了相位调制光栅防伪技术对调频加网方式和调幅全阶调潜像的提取,依赖原稿生成的不规则光栅具有抗复制性,使该防伪方法具有天然的防伪性能。

Linear gratings are only suitable for the amplitude modulation of images. To overcome this limitation, the anti-counterfeiting technology for phase-modulated latent images is studied based on the frequency-modulated image. The latent image is hidden in an error diffusion-screened image using the phase modulation method. Mutual information is considered to be the evaluation index of the hiding effect. An irregular grating is designed based on the grating extraction principle. Further, the application scope of the amplitude-modulated images is explored based on the concept of irregular grating design. The experimental results show that irregular gratings can clearly extract latent images from the frequency-modulated image and are suitable for the different tonality of the amplitude-modulated image. Thus, the applicability of the anti-counterfeiting technology based on phase-modulated grating for the frequency-modulated screening mode and amplitude-modulated full-tone latent image extraction is verified. The irregular grating obtained by relying on the original manuscript exhibits the property of anti-duplication, and endows the technique with natural anti-counterfeiting capability.