针对菲涅耳域双随机相位编码提出的一种改进图像加密系统。该系统通过预先将原图像编码为相位信息克服了原算法对第一块相位模板和第一次衍射距离不敏感的缺陷。在双随机相位编码模块后基于复值图像振幅及相位替代的再次加密，使得加密图像像素值分布更为均匀。另外，改进算法引入三种不同的混沌系统来生成所需要的随机模板，借助于混沌系统的非线性性、初值敏感性，加密系统在减小密钥体积的同时增大了密钥空间、增加了系统的复杂性。仿真实验对算法进行了有效性分析、统计分析以及密钥敏感性测试，结果表明改进的算法有效提升了原算法的安全性。

Aiming at the safety of double random phase encoding system in the Fresnel domain, an improved encryption algorithm is proposed. By means of the phase encoding in advance, the new system overcome the flaws of insensitivity to the first random phase mask and the first diffraction distance in original system. After the double random phase encoding module, the secondary encryption based on the amplitude-phase substitution of complex value image makes the pixel value distribution of encrypted image is more uniform. Random masks in the proposed algorithm are generated from three different chaotic systems. With the dynamics of chaotic systems, such as nonlinearity and sensitivity to initial values, the key volume is reduced, the key space is enlarged and complexity of the system is increased. Simulation is conducted on statistical analysis, correlation analysis and key sensitivity test. The experimental results show that the improved algorithm has higher security.