A real-time programmable joint transform correlator

A real-time programmable joint transform correlator (PJTC) utilizing a magneto-optic device (MOD) with a liquid crystal light value (LCLV) is presented. Object functions to be correlated are written into a light MOD with a programmable microcomputer, as input signals. Real-time correlation is taken place by a LCLV, as a square low detector, with a coherent read out. Cross correlation between the input functions can be obtained through the inverse Fourier transform of the read-out coherent illumination. A brief discussion of the proposed PJTC and a few experimental results are provided.     

CRT－LCLV and photorefractive crystl BSO based real－time joint transform correlator

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Optics based biohashing using joint transform correlator

Most authentication process uses password and personal identification numbers (PIN) for security purposes. In order to remove the problem of hacking or stealing of the password and PIN numbers, there has been an increased interest in the utilization of specific biometric feature of the user. Recently, biohashing systems have been introduced for automatic biometric recognition. In a biohashing system, biohash codes are generated using the feature of the biometric. A basic biohashing system involves two steps. First is the extraction of the feature from the input biometric image and second is the discretisation of the obtained feature vector by using ortho-normalized random numbers. In this paper, a new biohashing system has been proposed in which joint transform correlator (JTC) has been used for extraction of the specific feature of the biometric. In the enrolment process, a biohash code has been generated by using a single face image and then stored. In the verification process, this biohash code is matched with the verification codes for recognition purpose. The main advantage of the proposed biohashing method is the possibility of the optical implementation of the feature extraction of the face image. Experimental as well as simulation results have been given to validate the proposed technique. Normalized Hamming distance has been calculated to discriminate the genuine and impostor face images. By varying the dimension of the feature matrix, the study of the variation of the normalized Hamming distance with the density of the population has been undertaken. For the performance evaluation of the proposed technique the false rejection ratio (FRR) and false acceptance ratio (FAR) have also been calculated.     

Typewritten text identification using joint transform correlator

We describe some new results on the analysis of typewritten text using a joint transform correlator. The characters we consider are almost identical and binary (i.e. black on white) and we show that small differences, e.g. single pixel differences, cannot necessarily be detected from the correlation peak, but that the mean value of several pixels in the vicinity of the peak provides a discrimination measure.     

Contrast-improved joint transform correlator using spatial light modulators

When real time optical pattern recognition is carried out by means of spatial light modulators, a practical situation may arise in which the size of the Fourier transform and the intensity of the light source are fixed. Then, provided the input scene and the size of the spatial light modulator allow it, an interesting possibility for improving the overall intensity in the Fourier plane is the replication of the scene, either along a regular lattice structure or a random replication. In this work we analyse the usefulness of these methods, both to obtain diffraction images or cross-correlation between images in a joint transform correlator.     

利用液晶光阀作为位相调制器实现二元联合变换相关器

研究了液晶光阀(LCLV)作为位相调制器的特性,并用它实现了二元联合变换相关器.     

Wavelet-modified fringe-adjusted joint transform correlator

In this paper, we implement a wavelet-modified fringe-adjusted joint transform correlator (JTC) for real-time target recognition applications. In real-time situation the input scene is captured using a charge-coupled device (CCD) camera. The obtained joint power spectrum is multiplied by a pre-synthesized fringe-adjusted filter and the resultant function is processed with an appropriately scaled wavelet filter. Three performance measure parameters: correlation peak intensity, peak-to-sidelobe ratio, and signal-to-clutter ratio have been calculated for fringe-adjusted joint transform correlator (FJTC) and wavelet-modified fringe-adjusted joint transform correlator (WFJTC). The WFJTC has been found to yield better results in comparison to conventional FJTC. To suppress the undesired strong dc, the resultant function is differentiated. Differential processing wavelet-modified fringe-adjusted joint power spectrum removes the zero-order spectra and hence improves the detection efficiency. To focus the correlation terms in different planes in order to capture one of the desired autocorrelation peaks and discard the strong dc and another autocorrelation peak, chirp-encoding technique has also been applied. Targets with Gaussian and speckle noise have also been used to check the correlation outputs. Computer simulation and experimental results are presented.     

多目标识别的联合变换相关器的研究

提出了一种可用于多目标识别的联合变换相关器。为改善相关信号的性能,对功率谱作了优化处理。为消除相关面上的零级项和目标间的相关项,可用联合功率谱减去纯目标输入的功率谱和参考图像的功率谱;为增强和锐化相关峰,将相减的功率谱作指数函数滤波处理。分析了指数滤波参数对相关结果的影响。计算机模拟结果表明,这种相关器所输出的相关信号比经典联合变换相关器和二元联合变换相关器输出的相关信号更好,互相关得到了抑制,自相关得到了增强,具有很好的抗噪能力。     

Extended fractional wavelet joint transform correlator

An extended fractional wavelet joint transform correlator is implemented for real-time target recognition applications. The real-time input scene captured using a charge-coupled device camera along with the reference image is fractional Fourier transformed. The obtained joint power spectrum is multiplied by an appropriately scaled wavelet filter and the resultant function is differentiated. The application of wavelet filter enhances the correlation outputs and differential processing of wavelet-filtered joint power spectrum improves the detection efficiency by reducing the zero-order spectra. Targets with Gaussian and speckle noise have also been used to check the correlation output. The performance metrics: correlation peak intensity, peak-to-correlation energy, peak-to-sidelobe ratio and signal to clutter ratio have been calculated. The experimental results are presented in support of the proposed idea.     

Optical encryption using phase-shifting interferometry in a joint transform correlator

We propose an optical encryption technique where the encrypted field and the decrypting key are obtained by three-step phase-shifting interferometry and registered as digital Fresnel holograms in a joint transform correlator architecture. Decryption can be achieved by digital or optical means. The technique allows the complete process to be achieved at high speed and data to be transfered via digital communication channels. Experimental implementation is performed in a system based on a programmable liquid-crystal TV display working in pure phase mode to represent the input data and to introduce the required phase shifts. A CCD is used to register the output data.     

Compressive optical image watermarking using joint Fresnel transform correlator architecture

A new optical image watermarking technique based on compressive sensing using joint Fresnel transform correlator architecture has been presented. A secret scene or image is first embedded into a host image to perform optical image watermarking by use of joint Fresnel transform correlator architecture. Then, the watermarked image is compressed to much smaller signal data using single-pixel compressive holographic imaging in optical domain. At the received terminal, the watermarked image is reconstructed well via compressive sensing theory and a specified holographic reconstruction algorithm. The preliminary numerical simulations show that it is effective and suitable for optical image security transmission in the coming absolutely optical network for the reason of the completely optical implementation and largely decreased holograms data volume.     

Double-image encryption on joint transform correlator using two-step-only quadrature phase-shifting digital holography

A new double-image encryption method on the joint transform correlator using two-step-only quadrature phase-shifting digital holography, based on the calculated intensity of reference beam is proposed. The technique realizes the double-image encryption using one random phase encoding on the joint transform correlator; and only records two quadrature-phase holograms on CCD camera without recording reference-wave intensity or object-wave intensity. With the acquired reference-wave intensity from 2-D correlation coefficient and the keys known, the clear retrieved image can be obtained at high speed by certain algorithm. Its feasibility and validity were verified by a series of computer simulations.     

Subband mutiresolution by multi-object phase-only joint transform correlator

Subband multiresolution technique presents decomposition and reconstruction properties for 2D images using multichannel spatial filtering. Each subband image represents multiresolution of the input image. In this paper, optic subband multiresolution architecture is proposed based on multi-object phase-only joint transform correlator (JTC). Multichannel filtering is realized using multi-object input joint image that includes bipolar data. The bipolar data (containing positive, zero and negative values) is encoded by phase in the input and Fourier planes of the phase-only JTC. For image decomposition and reconstruction, two optoelectronic subband multiresolution architectures have been developed. Each architecture has been tested using a simulation program.     

Performance of an image-encrypted joint transform correlator for pattern recognition

An image-encrypted joint transform correlator for pattern recognition is proposed and evaluated. The correlator performs twofold correlation for recognizing the primary image and cipher, and the encrypting cipher acts to enhance or inhibit the correlation peak if the cipher is correctly input. By incorporating the original image with an appropriate cipher, the correlator achieves better pattern discrimination and is robust against distortion. Simulation results show that the pixel number and the cell size of cipher affect the characteristics of the correlator.     

Image displacement detection using double phase-encoded joint transform correlator based on wavelet denoising

Since double phase-encoded joint transform correlator (DPEJTC) cannot directly detect the motion between image frames of a video sequence with inadequate exposure, an image displacement detection method using DPEJTC based on log-Gabor wavelet denoising is proposed. The method uses a log-Gabor wavelet transform to denoise the reference and the target image obtained in the condition lack of enough exposure, preserving the phase information of them. Experimental results show that the method can successfully accomplish the motion detection. The technology improves the detection ability in conditions of low illumination and low contrast, showing great promise for motion detection under these circumstances. A possible hybrid electronic–optic setup is proposed.     

Effects of threshold on single-target detection by using modified amplitude-modulated joint transform correlator

Effects of threshold value on detection performance of the modified amplitude-modulated joint transform correlator are quantitatively studied using computer simulation. Fingerprint and human face images are used as test scenes in the presence of noise and a contrast difference. Simulation results demonstrate that this correlator improves detection performance for both types of image used, but moreso for human face images. Optimal detection of low-contrast human face images obscured by strong noise can be obtained by selecting an appropriate threshold value.     

Displacement measurement for color images by a phase-encoded joint transform correlator

Displacement measurement for color images using phase-encoded joint transform correlator (PJTC) is proposed. Color reference and target images are decomposed into red, green and blue components. We form new monochromic target and reference images by spatially arranging the three channels. The corresponding displacement of the color images is obtained using the PJTC with the new monochromic target and reference. Our method generates only one sharp peak, and could detect out the displacement of color images accurately. An appropriate hybrid-setup is proposed for pragmatic implementation.     

Known-plaintext attack on a joint transform correlator encrypting system

We demonstrate in this Letter that a joint transform correlator shows vulnerability to known-plaintext attacks. An unauthorized user, who intercepts both an object and its encrypted version, can obtain the security key code mask. In this contribution, we conduct a hybrid heuristic attack scheme merge to a Gerchberg-Saxton routine to estimate the encrypting key to decode different ciphertexts encrypted with that same key. We also analyze the success of this attack for different pairs of plaintext-ciphertext used to get the encrypting code. We present simulation results for the decrypting procedure to demonstrate the validity of our analysis.     

Chosen-plaintext attack on a joint transform correlator encrypting system

We demonstrate that optical encryption methods based on the joint transform correlator architecture are vulnerable to chosen-plaintext attack. An unauthorized user, who introduces three chosen plaintexts in the accessible encryption machine, can obtain the security key code mask. In this contribution, we also propose an alternative method to eliminate ambiguities that allows obtaining the right decrypting key.     

Displacement measurement based on joint fractional Fourier transform correlator

A displacement measurement technology based on joint fractional Fourier transform is firstly proposed. Contrast to conventional displacement measurement based on joint Fourier transform correlator, the position of cross correlation peak in the proposed technology could be fixed arbitrarily according to the order of fractional Fourier transform. The optical setup in the proposed technology is more flexible and easier to implement. Simulation and experiment results are given out to verify the analysis.