In order to improve the security of ciphertext image in transmission, a scheme of using neural network is proposed to restore the encryption-hiding images by using chaotic iris phase mask and double random phase encoding encrypted. To improve encryption performance, we replace the double random phase with chaotic iris phase masks. Firstly, the plaintext image is encrypted by improved double chaotic iris phase masks encoding, and the ciphertext image is generated. Then the ciphertext image is hidden into the carrier image through the Least Significant Bit (LSB) algorithm. It can avoid the detection to a certain extent. And a large number of hidden-plaintext image pairs are produced as a dataset. Secondly, the neural network is built in the process of continuous training and testing. The neural network selected in this paper is residual network (ResNet). The neural network to learn the logical relationship between input and output more efficiently, and successfully recovered the corresponding plaintext image. Finally, the trained neural network can fit the mapping relationship between the hidden image and the plaintext image. When decrypting, it is not necessary to extract the ciphertext image from the hidden image first and then decrypt it. This scheme can directly realize the decryption of hidden images. The paper elaborates the encryption, hiding and decryption process of the scheme in detail. Simulation experiments show that the scheme is feasible and has good robustness.
Based on chaotic biological cryptography and computer-generated holography, a symmetric–asymmetric hybrid encryption and decryption system was proposed. This method has multiple keys, in which two decryption keys are different from the encryption keys. The encryption and decryption system possesses both symmetric and asymmetric key cryptography features. The biometric code is unique and unchangeable, not easy to be stolen or lost, which further enhances the security of the system. Chaos technology can reduce the amount of information, when combined with the advantages of the digitization of computer-generated holography, which can be conducive to the preservation and the transmission of encrypted information. The numerical simulation results show that this scheme is feasible and has better security and higher robustness.
An encryption method combining optical digital holography with digital decryption on computer is proposed, which avoid the precise setup of optical devices. A digital hologram of three-dimensional (3D) object and a hologram of key information are recorded by optical method in the encryption process. The 3D object is reconstructed by filtering in spectrum domain and simple numerical calculation. The quality of reconstructed object is improved by reducing speckle noise. The robustness against occlusion and noise attacks of the system has also been analyzed. Optical experiments results are presented.
In this paper, an optical color image encryption/decryption technology based on joint fractional Fourier transform correlator and double random phase encoding (DRPE) is developed. In this method, the joint fractional power spectrum of the image to be encrypted and the key codes is recorded as the encrypted data. Different from the case with classical DRPE, the same key code was used both in the encryption and decryption. The security of the system is enhanced because of the fractional order as a new added key. This method takes full advantage of the parallel processing features of the optical system, and could optically realize single-channel color image encryption. The experimental results indicate that the new method is feasible.
A novel single-channel color image encryption technique based on joint fractional Fourier transform correlator(JFRTC)
and phase retrieval algorithm (PRA) is proposed. The target color image is decomposed into three red, green, blue (RGB)
components. A joint image is formed and encoded into two random phase masks (RPM) iteratively. The security of the
system is enhanced because of the fractional order as a new added key. The system and the operation procedure are
simplified. Simulation experiments show that the algorithm converges rapidly and has great design flexibility. The
decryption can be realized by digital or optical methods.
In this paper, a new system of multi-channel single-output
rotation-invariant joint fractional Fourier transform correlator
(JFRTC) for color pattern recognition is proposed. Due to the
shift-variant property of fractional Fourier transform (FRT),
we can obtain three correlation peaks at the output plane which show a pair of cross-correlation peaks that is desired and
one autocorrelation peak, so the noise is greatly reduced. The Synthetic discriminate function (SDF) is quoted at the
input plane to store the reference images to realize
rotation-invariant recognition. To optimize the correlation peaks, the
joint power spectrum is binarized to perform Fourier transform. The theoretical analysis and optical experiments are
discussed in detail. Experimental results are presented to demonstrate the ability of this system.
KEYWORDS: 3D image reconstruction, Digital holography, Speckle, Holograms, Holography, Digital imaging, Diffraction, Digital recording, Light scattering, Modulation
A fundamental problem in optical and digital holography is the existence of speckle noise in the reconstructed image.
Many approaches have been carried out in order to overcome this problem. In this paper a new technique to reduce the
speckle noise is proposed based on the physical nature of speckle noise. The illumination direction of the object beam is
changed to provide a different phase information for the same recorded object in an off-axis digital holographic setup
and the holograms are recorded with different illumination directions. Then the intensity information of the reconstructed
images is superposed and averaged to reduce the speckle noise. The theoretical analysis and experimental results are
shown to valid our proposal. They prove that the technique can effectively reduce the speckle noise without ruining the
object information.
Based on the extended fractional Fourier transform, we propose a zone-processing joint extended fractional Fourier
transform correlator. With the zone-processing technique, first, the high- and low-frequency zone can be obtained from
high- and low-brightness joint extended fractional Fourier transform power spectra, respectively. Second, they are
combined into new power spectra, so it can preferably include high- and low-frequency information simultaneously. The
experiment results demonstrate that this processing technique can largely improve correlation performance.
A technology for making multichannel fractional Fourier transform holograms (FRTHs) using a holographic lens array is proposed. With this method, the different-order FRTs can be produced simultaneously for multiple objects. This hologram records the information about both the object wave and the FRT system, including every fractional order, the focal length of every holographic lens, and the distance between the object and the holographic lens array. The FRTH cannot be reconstructed if system parameters are unknown, so this technology can improve the capability of optical anticounterfeiting techniques. Experiments have proved the theoretical analysis correct.
The multi-passage optical fiber faceplate, which has been successfully designed and made by us can exert direct effect on separating colors and encoding a transparent color film, so the encoded images will be sampled and compressed at the output end of the faceplate. Their coherent encoding images will be available when the three primary color images are written into a liquid crystal light valve (LCLV) and a laser beam is directed to read out these images through a polarizing beam splitter. Then, the read-out images will be transformed by a Fourier lens and recorded by a black-and-white film. Especially when the stored image is a color scene, preprocessing can be eliminated from the equipment proposed in this paper only by introducing a color CCD camera or an imaging system, coupled to the optical fiber faceplate's input end. The original color image can be also retrieved by the faceplate used in the opposite direction. The first-order diffractive image obtained from stored medium is written into the LCLV and a white light is directed to read out this image through a polarizing beam splitter, the read-out image should be accurately projected at the output end of the faceplate. These encoded images are colored by three primary color filters and transmitted to the input end of the faceplate. Thus, the stored original color image is retrieved.
A new stereogram holographic camera is designed by using the polarization and striped-speckle screen. It can be easily used to record a large scenery stereo-hologram. Furthermore, this hologram is illuminated with a white light, the stereogram can be observed without any appendant spectacles. This camera system consists of three parts: stereoscopic camera attachment, LCLV device, and rainbow holography system.
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