提出了一种基于光学衍射成像原理的彩色图像加密方法.首先把彩色图像分成红、绿、蓝三基色分量, 并将三基色灰度图像分别作离散余弦变换, 得到对应的离散余弦变换谱.保留离散余弦变换谱的主要数据, 并用空间复用的方法把这三个主要数据融合于一个实值图像之中, 该图像即为复合频谱.再将此复合频谱送入光学衍射成像系统中加密, 得到单幅密文.解密过程为加密过程的逆过程, 即首先由单幅密文恢复复合频谱, 再由复合频谱分离出三基色图像的部分离散余弦变换谱, 再对这些离散余弦变换谱做逆变换得到三基色图像.由于对复合频谱设置了一个特殊数据区, 因此在利用相位恢复算法恢复复合频谱的过程中, 这些特殊数据作为输入平面的部分振幅支撑, 可以避免迭代过程的停滞问题并提高收敛速率, 从而完全恢复复合频谱, 进而恢复原始图像.本方法可以将一幅彩色图像加密成单幅具有噪声图样的强度密文, 同时, 解密恢复得到的原始彩色图像具有较高的像质.

A method for color image encryption was proposed. For encryption, a color image is separated into three components which are red, green and blue. The three grey images are transformed with Discrete Cosine Transform (DCT). Then these DCT spectrums are partially retained and merged into a single real value matrix, namely the composite spectrum. Thereafter, the matrix is encrypted by the diffractive-imaging schemes. The decryption is the inverse of the encryption. Since a special domain has been set in the composite spectrum, the algorithm for retrieving the composite spectrum has overcome the stagnation problem and converges quickly. Computer simulations show that a color image can be successfully encrypted into a single noise-like intensity pattern, and the decrypted image can be obtained with high quality.