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A novel double-image encryption approach has been proposed based on optical interference and logistic map. Initially, original images are rearranged into two scrambled components with the use of the random sequence engendered based on the logistic map with the given conditions such as initial value and bifurcate parameter. One component is used as the input image of the framework of double random phase encoding and encrypted into the ciphertext. Another is decomposed into two phase masks, which are placed into the input plane and transform plane of double random phase encoding, respectively. To strength the nonlinearity of the cryptosystem, these phase masks considered as the main secret keys are further encoded by the aid of two random sequences. Because these keys are produced in the encryption process and directly related to original images, the proposed scheme has high resistance against the potential attacks such as chosen plaintext attack. Meanwhile, the parameters such as wavelength, axial distance, and conditions of the logistic map are considered as additional keys, which can enhance the security level further. Most importantly, the annoying silhouette problem existed in the interference-based encryption methods can be avoided effectively. A set of numerical simulations are presented to demonstrate the validity and feasibility of the proposed technique.

An optical approach of silhouette-free multiple-image encryption based on interference is proposed, with two layers to enhance the level of security. In the first layer, a group of plain images are encoded into an amplitude distribution, called interim, using the cascaded fractional Fourier transforms. In the second layer, the interim is encrypted into two noisy ciphertext images. The two layers are compactly combined into a single whole to assure that the inherent silhouette problem is removed through the involvement of a random phase-only mask as the built-in function of cryptosystem. In addition to the phase mask keys generated in the process of encryption, the security is enhanced further by considering the fractional order as an additional key. Numerical simulations are given to demonstrate the feasibility and validity of this approach.

A single-pixel correlated imaging scheme based on iterative phase retrieval algorithm, which can encode an original object into a series of measured intensities, is proposed in this paper. Initially, a plenty of intensity patterns are derived from the Hadamard matrix with the certain order, and a pair of noisy phase profiles can be obtained by decomposing an intensity pattern via an iterative phase retrieval algorithm. When a pair of phase profiles is cascaded and sequentially embedded into two spatial light modulators in the proposed optical configuration, a measured intensity can be recorded by the bucket detector without spatial resolution. By only making the use of second-order correlation algorithm, the object with high quality can be reconstructed with measured intensities. Meanwhile, the number of recording the measured intensities can be reduced greatly in the process of imaging, which results in high efficiency. The reported approach provides an effective alternative for enriching the related research on single-pixel correlated imaging systems.

A novel optical color image watermarking scheme considering human visual characteristics is presented in gyrator transform domain. Initially, an appropriate reference image is constructed of significant blocks chosen from the grayscale host image by evaluating visual characteristics such as visual entropy and edge entropy. Three components of the color watermark image are compressed based on compressive sensing, and the corresponding results are combined to form the grayscale watermark. Then, the frequency coefficients of the watermark image are fused into the frequency data of the gyrator-transformed reference image. The fused result is inversely transformed and partitioned, and eventually the watermarked image is obtained by mapping the resultant blocks into their original positions. The scheme can reconstruct the watermark with high perceptual quality and has the enhanced security due to high sensitivity of the secret keys. Importantly, the scheme can be implemented easily under the framework of double random phase encoding with the 4f optical system. To the best of our knowledge, it is the first report on embedding the color watermark into the grayscale host image which will be out of attacker's expectation. Simulation results are given to verify the feasibility and its superior performance in terms of noise and occlusion robustness.

A framework of computational ghost imaging based on the conditional adversarial network is proposed to efficiently implement the reconstruction of object images in this research. Although the traditional ghost imaging can recover object images with a few amount of measured intensities and corresponding speckle patterns, the visual quality of reconstructed images is seriously influenced by a lot of noise. To solve this issue, a conditional adversarial network is designed to improve the quality of the noisy images reconstructed by the traditional ghost imaging. The objective function is composed of multiple loss metrics, which avoid suffering from training instability of the network. Especially, the combination of critic loss and gradient penalty metrics guarantees that a wide variety of network architectures are used as the generator and almost no hyperparameter tuning is required in the network. Most importantly, the proposed network can be trained with simulated data without spending a long time to collect the practical training samples and considering the experimental condition. After training, the parameters of the network such as kernel weights of convolution filters are optimized from the adversarial process between the generator and the discriminator, object images can be perfectly reconstructed at a very low sampling ratio. Through the simulated and optical experiments, it is demonstrated that the proposed method has much better performance than other methods such as the traditional and compressive-sensing-based methods.

Single-pixel correlated imaging has been developed as one of the most promising techniques in the past decades. In this paper, a new mechanism of single-pixel correlated imaging is designed for multiple-image authentication. The object wave is sequentially modulated by a series of phase-only mask pairs embedded into two cascaded spatial light modulators. The modulated wave passes through the input image located in the object plane, and its intensity is recorded as one of the ciphertext values by using a single-pixel bucket detector without spatial resolution. The sparse data of plaintext images are obtained with the multiple-level wavelet transform and used to construct an interim image with the help of binary amplitude masks. The interim image with a smaller size than that of plaintext images is considered as the input of single-pixel correlated imaging, which can guarantee the number of measurements reduced. Simultaneously, the phase-only mask pairs are retrieved from the 2D patterns formed with the row vectors of the spatially orthogonal Hadamard matrix by using an efficient iterative phase retrieval algorithm. Because the redundancy between speckle patterns generated with these phase-only mask pairs is greatly restrained, the number of measurements can be further reduced. Moreover, the related binary amplitude masks are employed as the secret keys so that the security level is also extensively enhanced. Given the above, the proposed method can significantly achieve the goal of multiple-image verification and provide a different research approach for optical authentication based on single-pixel correlated imaging.

A two-layer watermarking scheme based on computational ghost imaging and singular value decomposition is proposed. In the first layer, the original watermark is encoded into a significantly small number of measured intensities in the process of computational ghost imaging to constitute a new watermark. In the second layer, the significant blocks chosen from the host image based on spatial frequency are combined to the reference image, which is used to embed the new watermark by using the singular value decomposition. Differing from other watermarking schemes, the information of original watermark can be verified without clear visualization via calculating the nonlinear correlation map between the original one and the reconstructed one. Besides optical parameters such as wavelength and propagation distance, a series of phase-only masks are used as security keys, which can enlarge the key space and enhance the level of security. The results illustrate the feasibility and effectiveness about the proposed watermarking mechanism, which provides an effective alternative for the related work.

In this paper, a novel information encryption scheme has been proposed based on the customized data container, where the primary information can be recovered completely from the ciphertext encrypted with computational ghost imaging. From two aspects, the proposed scheme solves the serious issues caused by the inherent linearity and mechanism of computational ghost imaging. First, the primary information to be encrypted is transformed into the bits of information, which is used to control the formation of the customized data container. Then, the exclusive-OR (XOR) operation is performed on it with a randomly generated data container, and the XOR encoding result is scrambled based on the random sequence engendered with the logistic map so that the linearity of the cryptosystem is destroyed. Second, instead of using random phase-only masks, a number of phase masks retrieved from 2D patterns derived from the rows of the designed Hadamard matrix are used to record the measured intensities. The redundancy between these phase masks is low, which can reduce the number of the required phase-only masks greatly. Meanwhile, the conditions of the logistic map are considered as the secret keys, which can enhance the security level greatly due to their high sensitivity to tiny variation. The validity and feasibility of the proposed method have been demonstrated with a set of numerical simulations. Published version

A novel optical image hiding scheme based on an expansion strategy is presented under the framework of computational ghost imaging. The image to be hidden is concealed into an expanded interim with the same size as the host image. This is implemented by rearranging the measured intensities of the original object after the process of ghost imaging. An initial Hadamard matrix is used to generate additional matrices by shifting it circularly along the column direction, so that enough 2D patterns are engendered to retrieve phase-only profiles for imaging. Next, the frequency coefficients of the host image are modified with that of the expanded interim by controlling a small weighting factor. After an inverse transform, the host image carrying the hidden information can be obtained with high imperceptibility. Security is assured by considering optical parameters, such as wavelength and axial distance, as secret keys due to their high sensitivity to tiny change. Importantly, differing from other computational ghost imaging based schemes, many phase-only profiles are used to collect the measured intensities to enhance the resistance against noise and occlusion attacks. The simulated experiments illustrate the feasibility and effectiveness of the proposed scheme. Published version

A novel computational ghost imaging scheme based on specially designed phase-only masks, which can be efficiently applied to encrypt an original image into a series of measured intensities, is proposed in this paper. First, a Hadamard matrix with a certain order is generated, where the number of elements in each row is equal to the size of the original image to be encrypted. Each row of the matrix is rearranged into the corresponding 2D pattern. Then, each pattern is encoded into the phase-only masks by making use of an iterative phase retrieval algorithm. These specially designed masks can be wholly or partially used in the process of computational ghost imaging to reconstruct the original information with high quality. When a significantly small number of phase-only masks are used to record the measured intensities in a single-pixel bucket detector, the information can be authenticated without clear visualization by calculating the nonlinear correlation map between the original image and its reconstruction. The results illustrate the feasibility and effectiveness of the proposed computational ghost imaging mechanism, which will provide an effective alternative for enriching the related research on the computational ghost imaging technique. Published version

A novel multiple-image encryption scheme using the nonlinear iterative phase retrieval algorithm in the gyrator transform domain under the illumination of an optical vortex beam is proposed. In order to increase the randomness, the chaotic structured phase mask based on the logistic map, Fresnel zone plate and radial Hilbert mask is proposed. With the help of two chaotic phase masks, each plain image is encoded into two phase-only masks that are considered as the private keys by using the iterative phase retrieval process in the gyrator domain. Then, the second keys of all plain images are modulated into the ciphertext, which has the stationary white noise distribution. Due to the use of the chaotic structured phase masks, the problem of axis alignment in the optical setup can easily be solved. Two private keys are directly relative to the plain images, which makes that the scheme has high resistance against various potential attacks. Moreover, the use of the vortex beam that can integrates more system parameters as the additional keys into one phase mask can improve the security level of the cryptosystem, which makes the key space enlarged widely. Simulation results are given to verify the feasibility and robustness of the proposed encryption scheme.