Study Of Biological Image Processing Based On Optical Encryption

Since optical encryption technology can process two-dimensional image data quickly and in parallel while hiding important information in different dimensions,it can provide more degrees of freedom for biological information security.The most traditional encryption technique is the double random phase encoding technique,which uses two random phase masks located at the spatial and spatial frequency domains respectively to encode the original image into white noise.However,the encryption key of the random phase encoding system is the same as the decryption key,i.e.,the encryption process is the same as the decryption process,which reduces the security of the system to some extent.In order to improve the security of double random phase encryption system,researchers have proposed many different encryption techniques based on the Fresnel transform,the fractional Fourier transform,the Gyrator transform,the Hartley transform.The distance of propagation and fractional order in the Fresnel transform and the fractional Fourier transform can be used as additional degrees of key dimension for the optical system.These extra keys add difficulty to the illegal attacker and increase the security of the system to some extent.The Fourier transform,Fresnel transform,and fractional Fourier transform belong to the category of the linear canonical transform,which can be optically implemented using quadratic phase systems.The Gyrator transform is also applied to optical encryption technology,where the parameters of the rotation angle provide additional degrees of freedom for the encryption system.Based on the random phase encoding technique,we try to explore new encryption techniques that provides more degrees of freedom.The main research contents of this paper are as follows:1.Optical heterodyne scanning encryption system for information security.In this system,the original image is encrypted and decrypted using random phase masks and an iris key.The phase and amplitude information of the optical wave field is completely preserved by incoherent light illumination.The process of encryption and decryption is very similar.One important difference is the pupil function.Different pupil functions make the optical transfer function different in the encryption and decryption process.Under the circumstance of the coding distance of encryption process is the same as the decoding distance of decryption process,the pupil function satisfies certain conditions and use the correct iris key and phase masks,the correct decryption image can be obtained.2.A novel fully phase encryption system is proposed in the fourth chapter based on optical interference principle and iterative phase retrieval algorithm.In the proposed encryption system,a random phase mask is applied as the unique encryption key.With the help of encryption key,the input secret image is numerically encoded into two phase masks,from which the diffraction patterns are visibly unrecognizable but comprises sufficient information for decryption.In encryption,the image to be encrypted and the encryption key are respectively used as the constraints in the input and output planes,from which the phase distributions of the encrypted results,i.e.,two phase masks that respectively placed in the input plane and the Fourier domain,can be calculated by using the proposed iterative phase retrieval algorithm.The encryption key used in the iterative process introduces the pixel scrambling of phase distribution in the input plane.Both the random phase mask,i.e.the encryption key and the two phase masks produced by using the iterative algorithm are indispensable in decryption.3.The fifth chapter proposes an image encryption technology based on phase recovery algorithm and divergent illumination.In this system,the fingerprint image is encoded into a preselected fake image by using an improved phase recovery algorithm.The encryption process of the algorithm cascades four phase-truncated Fourier transforms and inverse Fourier transforms.The decryption process is performed by an asymmetric coding system in which two phase masks are placed in the input plane and the conjugate plane,respectively.4.Optical image encryption and authentication based on the combination of random phase encryption technique and meta-surface materials.In this method,only a small number of pixels are used to encode the hologram phase information,while authentication results are still obtained successfully.