Practical image encryption and decryption by phase-coding technique for optical security systems.

A method of image encryption and decryption is proposed for optical security systems. A phase-coded image to be encrypted together with a random phase pattern is Fourier transformed and the result of the complex-valued data is used as an encrypted pattern. The decryption is simply performed by an inverse-Fourier transform for the addition of the encrypted pattern and the Fourier transform of the random phase. The intensity of the inverse-Fourier transformed image gives the exact result forthe decryption. Further, the binarization of the encrypted pattern is performed for the easiness of the optical and electronic readout of the images, and it also gives rise to the enhancement of the degree of security for the encryption. The binary pattern is optimized by a statistical iteration technique and an excellent decryption image is obtained by the optimization.