We investigate the performance of an image encryption technique that uses random-phase encoding in both the input plane and the Fourier plane, using partial information of the encrypted image. We first investigate the phase-only information of the encrypted data for decryption. A binary version of the phase-only information is also considered for decryption. Binary images are well suited for optical display and practical implementation. Using partial information of the encrypted image, a reconstructed complex image is generated, which is used for decryption. Tests are performed for both gray-scale and binary images. We show that the phase information of the encrypted image is very important in the reconstruction of the decrypted image. Computer simulations show that for the images tested here, binarization of the encrypted image can recover the original image with low mean squared error.

We propose a new technique for security verification of personal documents and other forms of personal identifications such as ID cards, passports, or credit cards. In this technique a primary pattern that might be a phase-encoded image is convolved by a random code. The information is phase encoded on the personal document. Therefore the information cannot be reproduced by an intensity detector such as a CCD camera. An optical processor based on the nonlinear joint transform correlator is used to perform the verification and the validation of documents with this technique. By verification of the biometrics information and the random code simultaneously, the proposed optical system determines whether a card is authentic or is being used by an authorized person. We tested the performance of the optical system for security and validation in the presence of input noise and in the presence of distortion of the information on the card. The performance of the proposed method is evaluated by use of a number of metrics. Statistical analysis of the system is performed to investigate the noise tolerance and the discrimination against false inputs for security verification.

In this work, we show some diffraction experiments performed with a liquid crystal display (LCD) that shows how useful this device can be to teach and experience diffraction optics and signal processing experiments. The LCD acts as a programmable pixelated diffractive mask. The Fourier spectrum of the image displayed in the LCD is visualized through a simple free propagation diffraction experiment. This optical system allows easy testing of different diffractive elements. As a demonstration we include experimental results with well-known diffractive elements like diffraction gratings or Fresnel lenses, and with more complicated elements like computer-generated holograms.

Abstract. 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. In this work, we propose a modification of the classical DRPE scheme based on the use of a novel 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 sub-keys. 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 new 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 gray-scale and binary images, may relax the rigidity of an encryptiondecryption experimental implementation set-up. To evaluate the effectiveness of the described method, the meansquare-error (MSE) and the peak signal-to-noise ratio (PSNR) 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 image encryption-decryption processes.