Image encoding based on coherent superposition and basic vector operations

A new method for image encryption based on optical coherent superposition and basic vector operations is proposed in this paper. In this encryption, the original image can be directly separated into two phase masks (PMs). One is a random phase mask (RPM) and the other is a modulation of the RPM by the original image. The mathematical calculation for obtaining the two PMs is quite simple and direct resulting from the simple principle of optical coherent superposition. The arbitrarily selected RPM can be treated as the encrypted result while the PM can be taken as the key for decryption. With this technique, the same encrypted result can be obtained for different images with the same size while the keys for decryption are different. The encryption can be performed digitally and the decryption can be performed optically or digitally. The security of the proposed method is discussed and computer simulation results are presented to verify the validity of proposed method.     

Color image encryption based on orthogonal composite grating and double random phase encoding technique

A new method of color image encryption based on orthogonal composite grating and double random phase encoding technique is proposed. The red (R), green (G) and blue (B) components of a color image to be encrypted is modulated into an orthogonal composite grating. The deformed composite grating is subsequently encrypted using double random phase encoding technique. At the decoding end, the deformed composite grating is decrypted through double random phase decoding system. By filtering in frequency domain and phase demodulating, the modulated RGB components can be recovered. Computer simulation experiments have proved the validity of the new method. The proposed method is also applicable to encrypt three color images simultaneously after they have been transformed respectively into indexed formats.     

双随机相位图像加密的实值编码研究

提出了一种基于双随机相位的图像实值编码方法,该方法可应用于光学图像加密.要编码的纯相位图像分别在空间域和频域加入随机相位掩膜,其中在频域将编码范围扩大4倍,经过光学系统的变换,将生成的图像取实部作为编码图像.实值编码的图像利用与编码过程类似的方法进行解码,可以准确地重建原图像.该编译码方法简单,编码图像是一个近似随机噪声的实值图像,便于数字图像的传输与输出.     

基于gyrator变换和矢量分解的非对称图像加密方法

本文结合矢量分解和gyrator变换的数学实现得到了一种新的非对称图像加密算法,它将待加密图像先通过矢量分解加密到两块纯相位板中,然后利用从gyrator变换的数学实现中推导出来的加密算法加密其中一块相位板,获得最终的实值密文.另一块相位板作为解密密钥.算法的解密密钥不同于加密密钥,实现了非对称加密,加密过程中产生的两个私钥增大了算法的安全性.数值模拟结果验证了该算法的可行性和有效性.     

Phase-Only Encryption and Single Path Decryption System Using Phase-Encoded Exclusive-OR Rules in Fourier Domain

A phase-only encryption scheme using phase-encoded exclusive-OR (XOR) rules in a Fourier plane and a single path decryption system are presented. To generate phase-only encrypted data, a zero-padded original image, multiplied by a random phase image, is Fourier transformed and its real-valued data is encrypted with key data by using phase-encoded XOR rules. Since the original information is encrypted on the Fourier plane, the proposed encryption is more tolerant to loss of key information by scratching or cutting than previous XOR encryption in a space domain. A decryption is simply performed based on 2-f setup with spatial filter by Fourier transform for multiplication phase-only encrypted data with phase-only key data. Due to single path architecture without a reference wave, the proposed system is resistant to mechanical vibrations and fluctuation. Numerical simulations have confirmed the validity of the proposed encryption scheme and simple decryption architecture.     

Image hiding based on time-averaging moiré

Image hiding based on optical time-averaging moiré technique is presented in this paper. It is a new visual decoding scheme when the secret image is embedded into a moiré grating and can be interpreted by a naked eye only when the image is harmonically oscillated in a predefined direction. The secret image is visualized at strictly defined amplitude of oscillation. Computational and experimental examples are used to demonstrate the functionality of the method.     

Optical image encryption by random shifting in fractional Fourier domains

A number of methods have recently been proposed in the literature for the encryption of two-dimensional information by use of optical systems based on the fractional Fourier transform. Typically, these methods require random phase screen keys for decrypting the data, which must be stored at the receiver and must be carefully aligned with the received encrypted data. A new technique based on a random shifting, or jigsaw, algorithm is proposed. This method does not require the use of phase keys. The image is encrypted by juxtaposition of sections of the image in fractional Fourier domains. The new method has been compared with existing methods and shows comparable or superior robustness to blind decryption. Optical implementation is discussed, and the sensitivity of the various encryption keys to blind decryption is examined.     

基于分数阶傅里叶变换的光学加密影片

随着通信与网络的快速发展,能够包含大容量信息的影片得到了广泛应用。利用分数阶傅里叶变换的特点,提出了一种全光学加密解密影片的方法。将现有的影片加密密钥从二重变为了四重,显著增加了影片的安全性。通过改变振幅型正弦光栅的作用位置,将影片的加密解密次数由现有的每帧各一次减小为总共一次,优化了算法。仿真结果验证了该方法的有效性。     

Interferometric phase-only optical encryption system that uses a reference wave

An improved image decryption system is proposed that is based on phase-encoded images and the principle of interference and uses a reference wave. A novel technique for generating intensity patterns from the decrypted phase information consists simply of interfering a reference wave with the wave passing through the encrypted image and a phase-only decrypting key. Optical experiments have confirmed the proposed technique as a simple and robust architecture for optical encryption.     

Optical retrieval of encrypted digital holograms for secure real-time display

Secure data transmission by use of encrypted digital holograms and an optical retrieval system for secure real-time display are proposed. Original images are encrypted by a double-random phase encryption technique and then are recorded as digital holograms in a CCD, together with a reference plane wave. This digital hologram of the encrypted image can be transmitted to receivers via any conventional electronic or digital communication channels. The decryption key is also recorded as a digital hologram. At the receiver, the original image can be retrieved by an optical correlation-based reconstruction process. Both encryption and retrieval can be performed by all-optical means, and thus a real-time secure display can be implemented. We demonstrate the proposed system numerically and experimentally.     

Image encryption and decryption using fractional Fourier transform and radial Hilbert transform

A technique for image encryption using fractional Fourier transform (FRT) and radial Hilbert transform (RHT) is proposed. The spatial frequency spectrum of the image to be encrypted is first segregated into two parts/channels using RHT, and image subtraction technique. Each of these channels is encrypted independently using double random phase encoding in the FRT domain. The different fractional orders and random phase masks used during the process of encryption and decryption are the keys to enhance the security of the proposed system. The algorithms to implement the proposed encryption and decryption scheme are discussed, and results of digital simulation are presented.     

Gray-Level Image Encryption Scheme Using Full Phase Encryption and Phase-Encoded Exclusive-OR Operations

A new gray-level image encryption scheme based on phase-encoded exclusive-OR (XOR) operations and a full phaseencoding method is presented. The gray-level image can be sliced into binary images which have the same pixel level, and each of them is encrypted by phase-encoded XOR operations with each phase-encoded binary random image. We combine XORed images and phase-encoded binary random images into an encrypted image and a key image, respectively. Gray-level encrypted data and key data are obtained by the phase-encoding process of the encrypted image and the key image in a space domain. The decryption process is simply implemented by using a phasevisualization system and the performance of the proposed scheme is evaluated by computer simulation.     

Optical image encryption using Hartley transform and logistic map

We propose a new method for image encryption using Hartley transform with jigsaw transform and logistic map. Logistic map has been used to generate the random intensity mask which is known as chaotic random intensity mask. The problem of bare decryption with Hartley transform has been solved by using the jigsaw transform. In the proposed technique, the image is encrypted using two methods in which the second method is the extension of the first method. In the first method, the image is encrypted using Hartley transform and jigsaw transform. In the second method, the image is encrypted using Hartley transform, jigsaw transform and logistic map. The mean square errors and the signal to noise ratio have been calculated. Robustness of the technique in terms of blind decryption and the algorithmic complexity has been evaluated. The optical implementation has been proposed. The computer simulations are presented to verify the validity of the proposed technique.     

基于随机相位实值编码的光学图像加密

提出了一种用于图像加密的随机相位实值编码方法,待编码的纯相位图像与一个随机相位掩膜一起作傅里叶变换,取其实部作为编码图像.已编码的图像和随机相位掩膜的傅里叶变换相加作傅里叶反变换,反变换的光强可以准确地重建原图像.该编译码方法简单,编码图像是一个实值图像,便于计算机打印或显示输出.     

Optical security system employing shifted phase-encoded joint transform correlation

A new optical security system is proposed using a shifted phase-encoded joint transform correlation (JTC) architecture. In the proposed technique, at first, the address code is fed into two channels where one channel is shifted by 180°. The output signals from both the channels are phase-masked and then added with the input image to be encrypted. The joint power spectrum (JPS) obtained from one channel is subtracted from the JPS of the other channel, and the modified JPS is inverse Fourier transformed to yield the encrypted image. For decryption, the received signal is Fourier transformed and multiplied by the phase mask and the address code, which is then inverse Fourier transformed to generate the output signal. The proposed technique does not require complex conjugate of the address code otherwise required in the classical double random phase encryption. Also the decryption result is much more enhanced when compared to the output generated by alternate JTC techniques. Computer simulation results verify that the encryption and decryption are very much secure and efficient in both noise-free and noisy conditions.     

Space-variant polarization scrambling for image encryption obtained with subwavelength gratings

We present an optical encryption method based on geometrical phase, which is originated from polarization manipulation. The decrypted picture is retrieved by measuring the polarization of the beam emerging from the encrypted element. The encrypted element is achieved by using a computer-generated space-variant subwavelength dielectric grating. Theoretical analyses of the optical concept by use of Jones and Mueller formalisms, as well as experimental results including full optical decryption process are introduced. Digital implementation and the possibility of using watermarking are also discussed.     

Gyrator transform-based optical image encryption,using chaos

We propose a new method for image encryption, using gyrator transform and chaos theory. Random phase masks are generated using chaos functions and are called as chaotic random phase masks. In the proposed technique, the image is encrypted using gyrator transform and two chaotic random phase masks. Three types of chaos functions have been used to generate the chaotic random phase masks. These chaos functions are the logistic map, the tent map and the Kaplan-Yorke map. The computer simulations are presented to verify the validity of the proposed technique. The mean square errors have been calculated. The robustness of the proposed technique to blind decryption in terms of rotation angle and the seed values of the chaotic random phase mask have been evaluated. The optical implementation of the encryption and the decryption technique has been proposed.     

Image encryption based on double random amplitude coding in random Hartley transform domain

We propose an image encryption scheme based on double random amplitude coding technique by using random Hartley transform, which is defined according to the random Fourier transform. The significant feature of this algorithm is that the encrypted image is real and convenient for storage as well as transfer of the encrypted information. Moreover, the algorithm has enhanced security and the correct information of original image can be well protected under bare decryption, blind decryption and brute force attacks. Numerical simulation results are also presented in support of the proposed scheme.     

Optical image encryption technique based on compressed sensing and Arnold transformation

A new optical image encryption method based on compressed sensing and Arnold transformation is proposed. First, dimensional reduction and random projection, the characteristics of compressed sensing, are utilized to compress and encrypt a digital image. Second, Arnold transformation is used to scramble the encryption image followed by compressed sensing with low data volume. Then, the encryption image is encrypted again by double random phase encoding optical encryption technique; two random phase masks generated by sequences of irrational number are been used as secret keys. In the end, the multi-encrypted information is embedded into the host image and transmitted. At the receiver, original image information is reconstructed approximately via orthogonal matching pursuit algorithm. The peak signal-to-noise ratio and the normalized cross-correlation between the original image and the decrypted one are used to calculate the quality of the decryption image. The experimental results demonstrate that our method is secure and robust.     

The phase shift method applied to cross grating moiré measurements

The automatic evaluation of the grating deformation in a moiré image is greatly enhanced by the phase shift method. Based on three or more local grey values of a related number of phase shifted moiré patterns, the local displacement of a deformed grating against a reference grating, and hence the total displacement in one direction, is calculated. In this paper an extension to cross gratings is presented yielding a two- dimensional displacement field.