KEYWORDS: Image encryption, Computer security, Image processing, Optical image encryption, Computer programming, Simulation of CCA and DLA aggregates, Optical engineering, Resistance, Fourier transforms, Information security
We propose an optical security technique for image encryption using triple random-phase encoding (TRPE). In the encryption process, the original image is first double-random-phase encrypted. The obtained function is then multiplied by a third random-phase key in the output plane, to enhance the security level of the encryption process. This method reduces the vulnerability to certain attacks observed when using the conventional double random-phase encoding (DRPE). To provide the security enhancement of the proposed TRPE method, three attack cases are discussed: chosen-plaintext attacks, known-plaintext attacks, and chosen-ciphertext attacks. Numerical results are presented to demonstrate feasibility and effectiveness of the proposed method. Compared with conventional DRPE, the proposed encryption method can provide an effective alternative and has enhanced security features against the aforementioned attacks.
The double-random phase encoding (DRPE) scheme, which is based on a 4f optical correlator system, is considered as a reference for the optical encryption field. We propose a modification of the classical DRPE scheme based on the use of a class of structured phase masks, the deterministic phase masks. In particular, we propose to conduct the encryption process by using two deterministic phase masks, which are built from linear combinations of several subkeys. For the decryption step, the input image is retrieved by using the complex conjugate of the deterministic phase masks, which were set in the encryption process. This concept of structured masks gives rise to encryption–decryption keys which are smaller and more compact than those required in the classical DRPE. In addition, we show that our method significantly improves the tolerance of the DRPE method to shifts of the decrypting phase mask—when no shift is applied, it provides similar performance to the DRPE scheme in terms of encryption–decryption results. This enhanced tolerance to the shift, which is proven by providing numerical simulation results for grayscale and binary images, may relax the rigidity of an encryption–decryption experimental implementation setup. To evaluate the effectiveness of the described method, the mean-square-error and the peak signal-to-noise ratio between the input images and the recovered images are calculated. Different studies based on simulated data are also provided to highlight the suitability and robustness of the method when applied to the image encryption–decryption processes.
In this work we propose the use of a liquid crystal spatial light modulator (LC-SLM) as a useful tool to teach and experience diffraction and signal processing. The LC-SLM acts as a programmable pixelated diffractive mask. The Fourier spectra of the image displayed in the LC-SLM is visualized through a simple free propagation diffraction experiment. This optical system allows easily testing different diffractive elements and performing several signal processing experiments. As a demonstration we include experimental results with diffraction gratings, computer generated holograms, diffractive lenses and axicons.
In this paper we present the research line that we develop in pattern recognition of multichannel images, centered in the application of color images. Pattern recognition is performed through a multichannel correlation process. The correlation is applied to each channel, red, green and blue of the color image. The final recognition result is obtained by a combination of the information of the three monochromatic correlations. Two different approaches are proposed in order to improve the discrimination capability of the multichannel process. First, element-wise transformations over the multichannel images are used in order to enhance differences between channels. Then, the information in each channel is independent and the autocorrelation is enhanced with respect to the cross- correlations. The second approach involves the optimization of the matched phase-only filters used in every channel. This optimization is performed by means of a region of support. They are two complementary techniques that increase the discrimination capability and eliminate false alarms. The result is a better performance of the multichannel correlator for pattern recognition.
In this paper we present some results on the research line of real-time correlation applied to optical pattern recognition. We present a real time optical correlator that uses two twisted nematic liquid crystal spatial light modulators (SLM). This kind of SLM produces phase and amplitude coupled modulation. Phase modulation is useful for the implementation of phase only filters (POF), but the coupled amplitude modulation affects its performance. We present a model to evaluate the response of the phase-only filter (POF) implemented on a modulator with a restricted modulation and we show results on the optimal implementation of POF of this restricted coding domain. The phase modulation is also used for the implementation of the scene by means of a phase-encoding algorithm. The performance of the phase-only filter has been improved for several performances criteria by the design of binary amplitude masks. We present a technique for the implementation of these optimized binary amplitude phase-only filters using phase-mostly SLMs. Results obtained for the optimization of different criteria are presented. Finally, we present results on the application of these methods to color pattern recognition problems by a multichannel correlation.
In this work we summarize some of the work of our team in the last years, devoted to the use of spatial light modulators (SLM) in optical correlators and optical image processors. We have built an optical processor that uses two liquid crystal SLMs, one to implement the image to be processed and a second one to implement a Fourier filter. We analyzed the advantages of the use of SLMs, but also the restrictions they impose. We proposed several architectures and filters design to take profit of this SLM based optical processor.
In this work we present a method to implement optimized binary amplitude phase only filters with spatial light modulators that produce phase only modulation. The technique consists in the addition of linear or quadratic phase codes to the phase distribution of the phase only filter in those pixels that must not blocked in the binary amplitude phase only filter. This technique permits to separate the optimized correlation. Numerical simulation and experimental results are presented.
We compare two methods for optimizing the discrimination capability of phase only filter by designing a function of support. First, we study a method based on simulated annealing. Second, we propose a method in which we consider the correlations at the origin. The last one reduces very much the computing time. In all the cases we have studied, the proposed method arrives at better results than with simulated annealing.
A review of the multichannel correlation methods applied to discriminate color objects with the logical operation AND is presented. The effects of the color CCD camera as the acquisition system are studied. A preprocessing method is proposed to increase the discrimination. The generation of the filters is improved by applying lithographic techniques. Finally an approach of the optimal filter proposed by Yaroslavsky is applied to each channel in the correlation process. Computer and experimental results are given.
Different linear and non linear edge extraction methods applied as preprocessing to the scene to the target or to both are studied in pattern recognition based on correlation. Results for binary and grey level objects are given.