【作者】 陆红强；

【导师】 赵建林；

【作者基本信息】 西北工业大学 ， 光学工程， 2005， 硕士

【摘要】 随着互联网技术的迅速发展和对大量图像信息传输需求的日益增加,图像加密技术已变得越来越重要。由于光学信息处理系统的高度并行性和超快处理速度,使得很多光学加密系统被提出并且运用于信息安全领域。本文通过对傅里叶变换、分数傅里叶变换和像素置乱技术的分析与讨论,提出了基于像素置乱技术的傅里叶变换加密法和分数傅里叶变换加密法,并且对这些加密法进行了理论分析和数值计算。本文主要内容如下: (1) 从理论和仿真计算的角度论证了基于傅里叶变换的加密法的可行性和可靠性。从仿真计算得到用部分加密图像解密也能够得到原始图像,同时还给出了解密图像的能量、噪声及其信噪比随着待解密的加密图像像素的变化曲线。由于引入了像素置乱操作,故该加密法的保密性得到提高。 (2) 由于分数傅里叶变换的空-频联合表象特性,本文提出了基于分数傅里叶变换的光学图像加密法,同时还提出了彩色图像加密法。仿真结果证实了这两种加密法,并且给出解密图像的相对误差与不同分数傅里叶变换级次偏离量△p的关系,与傅里叶变换加密法相比,这两种加密法的保密性能被大大提高。 (3) 具体地分析和讨论了线性正则变换、空间光调制器和置乱变换对维格纳分布函数的影响,从而导出了能够自动、有效地计算加密/解密过程中任意平面上信号的位置、空域宽度、频域宽度和空间带宽积的矩阵方法。通过该方法可以确定合适的加密系统和光学器件,例如输入信号的空间带宽积、变换透镜的最小孔径、空间光调制器的分辨率和像素大小、CCD的分辨率和像素大小以及入射到空间光调制器和CCD靶面上光场所需的放大倍数。更多还原

【Abstract】 With the development of Internet and the increase of the requirement for image transmission, information security and data encryption are becoming more and more important. Many optical systems have been proposed and used in data security field for the distinct advantages of processing complex two-dimensional data in parallel and transmitting at great speed. By analyzing and discussing the techniques of Fourier transform, fractional Fourier transform and pixel scrambling, methods of Fourier transform encryption as well as fractional Fourier transform encryption have been proposed and numerically simulated. The principle work is as follows:(1) The flexibility and reliability of optical image encryption methods based on Fourier transform are theoretically and simulatively proved. It is shown form numerical simulation that the original image can be reconstructed only when part of the encrypted image is used. The relationship curves between pixels number of the decrypting image and the energy, noise as well as SNR of the decoded image are given. By introducing pixel scrambling, the security strength of proposed method is greatly improved.(2) Based on the space-frequency joint representation features of fractional Fourier transform, a novel optical image encryption method and an improved color image encryption method are both proposed. These methods are proved by simulation, and the relative error between original image and decoded image versus the deviation of different fractional orders Ap is also discussed. Compared with Fourier transform encryption, the security using these two methods for optical image encryption is greatly improved due to the introduction of the fractional Fourier transform.(3) By analyzing the effects of linear Canonical transform, a spatial light modulator and pixel scrambling on the Wigner distribution function, we derive a matrix method for automatically and efficiently determining the position, spatial extent, spatial frequency extent and the space bandwidth product of the signal at any point in the encryption process including the values of the these parameters in the final encrypted image. This method also allow us to select the most efficient way from the bulk optical systems and available recoding methods, i.e., identifying the space bandwidth product of the input signal, the minimum size of lens apertures, the sample space and total sample number of CCD and spatial light modulator, the need of magnification before the signal passes through a SLM or when the signal reaches the camera.更多还原