The optical image compression and encryption method based on Fresnel diffraction and discrete wavelet transform

Generally, the length of ciphertexts and encryption keys are usually longer than that of the plaintexts. In this study, an optical image compression method based on Fresnel diffraction and discrete wavelet transform is proposed. The Fresnel diffraction is used for acquiring more low-frequency information. The proposed method is a plaintext pre-processing scheme and can be adopted in any cryptosystem where the encryption key cannot be shortened effectively. In this method, we can obtain a compressed image whose length is shorter them the plaintext. By encrypting the compressed image obtained, the length of ciphertext and encryption keys can be reduced. In addition, some compression parameters naturally existed in the proposed Fresnel diffraction optical setup are also needed for decompression. Moreover, the proposed method can also further compress the plaintext if a slight increment of information loss is allowed. Besides, the realization of this scheme is simple, hence no substantial cost is added for a given optical cryptosystem. Besides the statistical analysis, extensive numerical simulations have been carried out to validate the feasibility, robustness, sensibility of the proposed method.