基于计算全息和迭代傅里叶变换算法的光学图像加密技术的研究

【作者】 王永瑛；

【导师】 王玉荣；

【作者基本信息】 山东大学 ， 光学工程， 2007， 硕士

【摘要】 随着信息技术的迅猛发展，数据加密、防伪和安全认证等信息安全问题变得越来越重要。在计算机和电子信息加密技术得到广泛应用的同时，光学加密技术的研究在过去十几年中发展很快，这源于光学信息处理技术固有的高速、并行及多维编码(相位，波长、空间频率、偏振等)信息处理能力，已有很多光学加密原理和技术系统被提出。在这些原理和技术中，最引人注目的是由B Javidi等人于1995年提出并在近几年来渐渐发展起来的双随机相位编码光学加密方案。本文总结了基于双随机相位编码光学加密的多种图像加密方法，并结合迭代傅里叶变换算法、傅里叶变换计算全息图及图像像素置乱等技术，提出了几种新的图像加密方法，并且对这些加密法进行了理论分析和数值计算。本文工作主要包括以下几个方面：(1)综述了光学图像加密技术的研究历史和现状。简要介绍了光波标量衍射、光学傅里叶变换、衍射光学元件设计、计算全息编码等基本理论与方法。(2)详细介绍了迭代傅里叶变换算法，光学4f系统，联合变换相关器，及基于上述系统的光学图像加密方法，并进行了计算机仿真与验证。(3)基于傅里叶计算全息编码和图像像素置乱技术，提出了一种新的图像加密方法，由于该方法所得的加密图像为一幅二值振幅图像，便于制作的同时，也大大增强了其鲁棒性，通过计算机模拟仿真，对该方法及其鲁棒性进行了分析，并从光学实验上验证该论文所提出的新方法。(4)基于光学4f系统及迭代傅里叶变换算法，提出前向迭代多随机相位光学图像加密方法，从迭代收敛速度、解密图像质量、相位板数目与相位量化阶数对解密图像质量的影响、以及保密与安全性能等方面，对该方法进行了分析比较研究。计算机模拟实验结果表明：该方法收敛速度快，解密图像质量好，可以降低相位板相位量化阶数有限所引起的误差对解密图像质量的影响，图像的安全与保密性能也大大提高。(5)在虚拟光学数据加密理论的基础上，基于光学4f系统及迭代傅里叶变换算法，提出利用多个相位板进行分级图像加密的方法，将不同密级的图像分别加密到不同的相位板中，此方法可将信息进行分级加密，用于对不同权限级别的用户开放，可用于安全认证和准入检查系统，给出了其原理和实现方法，并通过计算机模拟验证了该方法的有效性。更多还原

【Abstract】 With the rapid development of Internet, data encryption, anti-counterfeiting application and information security are becoming more and more important. Compare with the traditional computer and electrical systems, optical technology for information security have received increasing interests in the past decade because of its distinct advantages: (1) Optical systems have an inherent capability for parallel processing, that is, rapid transmission of information. (2) Information can be hidden in any of several freedoms, such as phase, wavelength, spatial frequency or polarization, that is, optical systems have excellent capability for encoding information. Many optical systems have been proposed and used in verification and data encryption. Among those architectures the most attractive one is the so-called double random phase encoding technique proposed by B. Javidi and coworkers in 1995.The aim of this thesis is to give a comprehensive review on the double random phase encoding technique, and then propose and numerically simulate some novel methods and techniques of optical image encryption, which are based on the Iterative Fourier Transform Algorithm (IFTA), binary Fourier transform computer-generated hologram and pixel scrambling technology. The main research work in this thesis includes the following:(1) This thesis reviews the progress of the optical image encryption, and gives a general introduction about optical scalar diffraction, optical Fourier transform, design methods for diffractive optics element and the theory of the Computer Generated Hologram.(2) The Iterative Fourier Transform Algorithm, 4/system, joint transform correlator, and the optical image encryption based on these techniques are introduced in detail, and the computer simulations are given.(3) A new method of optical image encryption with binary Fourier transform computer-generated hologram (CGH) and pixel scrambling technology is presented. Because the encrypted image is a binary image, so it is easy to be fabricated and robust against noise and distortion. Computer simulation and experimental results are given to verify the feasibility of this method and its robustness against occlusion and additional noise.(4) The method of the multiple-random-phase by use of forward iterative phase retrieval algorithm for optical image encryption is described and demonstrated with computer simulation experiments. The convergent speed of the method is significantly increased and the decrypted image is similar to the target image. The errors caused by the quantization of phase masks are decreased with the proposed method. The relationships between the numbers of phase masks and quantized phase levels are also discussed by the results of computer simulation. In addition, with more phase keys, the security and secrecy of image are greatly increased. Computer simulations are demonstrated to verify the proposed method.(5) A novel approach - multiple phase encoding for hierarchical security by use of a 4f optical system and iterative Fourier transform algorithm is presented, which is based on the methodology of virtual optics. Two or more phase masks produced by multiple iterative Fourier transform algorithm are used in this hierarchical security system, in which different target images can be retrieved by use of different numbers of phase masks. In addition to the application of hierarchical data encryption, the system can also provide the verification of the identity of the persons legally wishing to access it. Simulation results indicate that our proposed system is effective and efficient.更多还原