Esmail Ahouzi

Performance of double phase encoding encryption technique using binarized encrypted images

We investigate the performance of an image encryption tech- nique 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 decryp- tion. 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 re- constructed 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 re- cover the original image with low mean squared error.

Phase-only filter with improved discrimination

The optimization of a phase-only filter (POF) in terms of discrimination capability is presented. The notion of a phase-difference histogram and its modification are proposed for selecting the support function of the POF. Some numerical results obtained with the conventional POF and the optimized POF are given. The discrimination capability is increased significantly.

Nonlinearity effects in the pure phase correlation method in multiobject scenes

The nonlinearity used in the pure phase correlation method can improve pattern recognition, but it causes high-order harmonics in the correlation plane in the case of multiobject scenes. High-order harmonics and the presence of aliasing may cause false alarms. We show that these effects are strongly diminished when the periodicity in the scene is broken (by different objects, random distribution, etc.).

Diffraction and signal processing experiments with a liquid crystal microdisplay

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.

Optoelectronic pure phase correlator

Abstract An architecture based on a classical convergent correlator to obtain the pure phase correlation is proposed. The effects of the amplitude transmission of the filter and the effects of the quantization introduced by the CCD camera are studied in terms of correlation performance by computer simulation.

Optical image encryption technique based on deterministic phase masks

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. 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.

Binary amplitude phase-only filter with high multiobject discrimination capability

Universidad Auto´noma de BarcelonaDepartamento de Fi´sicaBellaterra, Barcelona 08193SpainE-mail: ifop1@cc.uab.esAbstract. Binary amplitude phase-only filters (BAPOFs) with high dis-crimination capability (DC) are presented. This enhancement is achievedby designing the region of support of the phase-only filters (POFs). Wepropose different approaches for maximizing the DC based on analyticalexpressions of the correlation function for real-valued input scenes.Computer simulation and experimental results are presented and dis-cussed. The experimental results coincide with the numerical analysisand demonstrate that the optimized BAPOFs obtained with this newtechnique produce high discrimination capability among several objects.For comparison, the optimization of the DC of the POF is formulated asan annealing problem.

Optimization of the polychromatic discrimination capability in multichannel pattern recognition

We present the improvement of color pattern recognition by the optimization of a new parameter, the polychromatic discrimination capability. We use the polychromatic correlation obtained as the addition of the three correlation intensities obtained with the RGB components of the input color scene and the corresponding components of the color target. The polychromatic discrimination capability is defined in this fused correlation plane. We propose a method to optimize this perfor- mance parameter, which represents a global criterion for the optimization of the polychromatic correlation. The approach involves the design of regions of support to be used with the matched phase-only filters to optimize the polychromatic discrimination. We present simulation results illustrating the improvements obtained after the optimization process. We also include experimental results obtained with an optical real-time cor- relator that uses two spatial light modulators. Experimental data confirm the numerical results and show the capacity of the proposed technique to improve color pattern recognition.

Pure Phase Correlation with Improved Discrimination Capability

Pure phase correlation with improved discrimination capability is proposed. The improvement is achieved by designing a region of support based on the discrimination capability (DC). We propose four approaches for designing this region; some of them consider the input scene in the design, while others are input scene invariant. The performances of these approaches are compared by numerical simulation. The DC is improved significantly for the multi-object scenes even when using an input scene invariant region of support design.

Multichannel pattern recognition of color images

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.