基于空域-分频域混合编码的光学图像加密

为了提高现有光学安全系统的安全性能，首次提出“空域-分频域(分数傅里叶域)”混合编码的光学图像加密方法。该方法对图像分别进行一次菲涅耳变换和分数傅里叶变换，并在图像的菲涅耳域和分数傅里叶域上分别利用随机相位版施行相位编码。在加密过程中，上述两次变换的参数均可以设计成密钥．波长因子也可以引入加密过程，这样系统密钥被设计在两个不同的变换域上，提高了系统的安全性能。计算机仿真试验表明，该加密方法能够成功实现图像的加密和解密，系统对密钥参数十分敏感．非授权认证方在不知道密钥参数的情况下几乎不可能对加密图像正确解密。

Encrypting optical image based on compound encoding on space-fractional domain

For the improvement of security capability of existing optical security system, a novel method for encrypting optical image using encoding on both space domain and fractional Fourier domain is presented. In this paper, image is Fresnel transformed and Fractional Fourier transformed successively, and phase encoding is implemented in both Fresnel domain and Fractional Fourier domain. The parameters in two transform can be designed as keys, and the wavelength-key can also be introduced into the encryption process successfully, then the keys of the security system are set on different domains, which can improve the security capability of the system. Computer simulation indicates that the method proposed in this paper can encrypt and decrypt image successfully, and the decrypted results are very sensitive to the keys, people unauthorized can hardly decrypt the image correctly without knowing them.