Joint Transform Correlator Research Articles

DNA sequencing using optical joint Fourier transform

An optical image processing technique is proposed for analyzing and exploring DNA sequences. The proposed approach uses the powerful computing capability of optical correlation to provide real-time processing of the genomic data. Instead of representing the symbolic DNA sequences in numeric form, they are converted and treated as 2-D images for matching purposes. Both images of the reference and the target DNA sequences are combined and presented as a joint input image to an optical joint transform correlator (JTC) set-up for a real-time processing. This JTC-based approach is capable to search for similarity/dissimilarity between two tested DNA sequences. The proposed optical approach facilitates the exhaustive search algorithms for locally and/or globally DNA alignment. Simulations experimental results on actual DNA sequences are presented to demonstrate the effectiveness of the proposed optical approach.

Processing of 1D signals with raster input in 2D optical correlators

The feasibility of Vander-Lugt and joint-transform optical correlators for the correlation processing of large-base 1D signals is demonstrated. The results of experiments with a joint-transform correlator with a liquid-crystal input device and raster input of a signal are presented.

Assessing the performance of a motion tracking system based on optical joint transform correlation

We present an optimized system specially designed for the tracking and recognition of moving subjects in a confined environment (such as an elderly remaining at home). In the first step of our study, we use a VanderLugt correlator (VLC) with an adapted pre-processing treatment of the input plane and a postprocessing of the correlation plane via a nonlinear function allowing us to make a robust decision. The second step is based on an optical joint transform correlation (JTC)-based system (NZ-NL-correlation JTC) for achieving improved detection and tracking of moving persons in a confined space. The proposed system has been found to have significantly superior discrimination and robustness capabilities allowing to detect an unknown target in an input scene and to determine the target’s trajectory when this target is in motion. This system offers robust tracking performance of a moving target in several scenarios, such as rotational variation of input faces. Test results obtained using various real life video sequences show that the proposed system is particularly suitable for real-time detection and tracking of moving objects.

Image rotation and translation measurement based on joint transform correlator

An image rotation and translation measurement technology based on joint transform correlator (JTC) is proposed. The reference and the target images are Fourier transformed. Then the magnitude of the Fourier transformed reference (MFR) and target (MFT) images are multiplied with a high-pass emphasis filter and transformed from Cartesian space into Polar space. The rotation between the reference and the target image is obtained by measuring the filtered MFR and MFT in polar coordinates by JTC. Rotate the target image in reverse orientation by the rotation angle to get the rotation-corrected target (RCT) image. Finally the translation between the reference and the target image is obtained through measuring the reference and the rotation-corrected target image by JTC. Simulational and experimental results are given to verify our analysis.

Optical Fourier processor with a liquid-crystal information-input device

A working prototype of an optical system has been developed for processing signals and images, using a liquid-crystal array with electronic control to input the information. A number of information-processing setups have been investigated that are implemented on the basis of the developed prototype. These include an analyzer of the spatial spectra of the images and signals, a joint-transform correlator, a spectrum analyzer, and a correlator of long signals with a convoluted spectrum. There are 1024×768 elements in the input array, and the information-renewal frequency is 70 frames per second. The prototype thus developed is used as the basis for creating a laboratory project for physically modelling and studying the operation of optical information-processing systems.

Image Blurring Estimation and Calibration with a Joint Transform Correlator

The Joint Transform Correlator (JTC) has been the most suitable technique for real time optical pattern recognition and target tracking applications. This paper proposes a new application of the JTC system for an analysis of the blurring effect of the optical images caused by a defocused lens. We present the relation between the correlation peak, optical transfer function (OTF), and the amount of blurring caused by focusing error. Moreover, we show a possibility of calibrating the blurred image by simply measuring the correlation peak.

Generalized formulation of an encryption system based on a joint transform correlator and fractional Fourier transform

We propose a generalization of the encryption system based on double random phase encoding (DRPE) and a joint transform correlator (JTC), from the Fourier domain to the fractional Fourier domain (FrFD) by using the fractional Fourier operators, such as the fractional Fourier transform (FrFT), fractional traslation, fractional convolution and fractional correlation. Image encryption systems based on a JTC architecture in the FrFD usually produce low quality decrypted images. In this work, we present two approaches to improve the quality of the decrypted images, which are based on nonlinear processing applied to the encrypted function (that contains the joint fractional power spectrum, JFPS) and the nonzero-order JTC in the FrFD. When the two approaches are combined, the quality of the decrypted image is higher. In addition to the advantages introduced by the implementation of the DRPE using a JTC, we demonstrate that the proposed encryption system in the FrFD preserves the shift-invariance property of the JTC-based encryption system in the Fourier domain, with respect to the lateral displacement of both the key random mask in the decryption process and the retrieval of the primary image. The feasibility of this encryption system is verified and analyzed by computer simulations.

Location Technology of Correlation Peaks Based on Joint Transform Correlator

By comparing the similarity of their contour information, hybrid photoelectric joint transform correlator (JTC) is used to recognize the specific target. An effective method to increase the recognition rate is to extract the contour information of target and template and decrease the noise interference in image background. The principle of joint transform correlator is given in this paper. To increase the recognizing rate, a mask algorithm is presented, with which the coordinate of the correlation peaks can be located precisely. Before the mask algorithm, edge extraction with Robert operator is carried out to enhance the target contour information and reduce the background noise. Amounts of experiments prove the mask algorithm can locate the correlation peaks precisely. As an example, an experimental result is given with a car as the detected target. The coordinate of this car is (362, 438). Experimental results confirm the feasibility and effectiveness of the mask algorithm.

Nonlinear optical security system based on a joint transform correlator in the Fresnel domain

A new optical security system for image encryption based on a nonlinear joint transform correlator (JTC) in the Fresnel domain (FrD) is proposed. The proposal of the encryption process is a lensless optical system that produces a real encrypted image and is a simplified version of some previous JTC-based encryption systems. We use a random complex mask as the key in the nonlinear system for the purpose of increasing the security of the encrypted image. In order to retrieve the primary image in the decryption process, a nonlinear operation has to be introduced in the encrypted function. The optical decryption process is implemented through the Fresnel transform and the fractional Fourier transform. The security system proposed in this paper preserves the shift-invariance property of the JTC-based encryption system in the Fourier domain, with respect to the lateral displacement of the key random mask in the decryption process. This system shows an improved resistance to chosen-plaintext and known-plaintext attacks, as they have been proposed in the cryptanalysis of the JTC encrypting system. Numerical simulations show the validity of this new optical security system.

Improvement of image deblurring for opto-electronic joint transform correlator under projective motion vector estimation

In this paper we propose an efficient algorithm to improve the performance of image deblurring based on opto-electronic joint transform correlator (JTC) that is capable of detecting the motion vector of a space camera. Firstly, the motion vector obtained from JTC is divided into many sub-motion vectors according to the projective motion path, which represents the degraded image as an integration of the clear scene under a sequence of planar projective transforms. Secondly, these sub-motion vectors are incorporated into the projective motion Richardson–Lucy (RL) algorithm to improve deblurred results. The simulation results demonstrate the effectiveness of the algorithm and the influence of noise on the algorithm performance is also statically analyzed.

Images encryption system based on a fractional joint transform correlator and nonlinear filtering

A new optical security system for image encryption based on a fractional joint transform correlator and nonlinear filtering is proposed. The position of the lens in the proposed optical encryption setup can be chosen, so that an additional key is introduced in the security system. The distributions at the input and output planes of the encryption system are related by a fractional Fourier transform (FrFT) at a given fractional order that is defined, among other parameters, by the focal length and the position of the lens in the setup; this fractional order acts as an additional key of the security system. The optical intensity of the complex distribution in the fractional Fourier domain (output plane) is captured by a CCD camera. The nonlinearity introduced in the last step of the encryption process, maintains the encrypted function as a real-valued function. The security system proposed in this work is an generalization of the encryption system based on a conventional joint transform correlator (JTC), from the Fourier domain to the fractional Fourier domain. Additional advantages of the proposed system are: new degrees of freedom for the optical setup, alleviated alignment requirement, and the introduction of an additional key (the fractional order of the FrFT) that improves security. Numerical simulations verify the validity of this new optical security system.

Ciphertext-only attack on a joint transform correlator encryption system

A ciphertext-only attack (COA) on a joint transform correlator (JTC) encryption system is proposed. From the perspective view of optical cryptanalysis, we find out that the issue to be solved in the COA scheme could be transferred into a phase retrieval problem with single intensity measurement. And in this paper, the hybrid input-output (HIO) algorithm is employed to handle this issue with the help of an inartificial signal domain support and a given frequency domain constraint. Meanwhile, we provide a set of numerical simulations to demonstrate the validity and feasibility of the presented method.

Hierarchical clustering of EMD based interest points for road sign detection

Abstract This paper presents an automatic road traffic signs detection and recognition system based on hierarchical clustering of interest points and joint transform correlation. The proposed algorithm consists of the three following stages: interest points detection, clustering of those points and similarity search. At the first stage, good discriminative, rotation and scale invariant interest points are selected from the image edges based on the 1-D empirical mode decomposition (EMD). We propose a two-step unsupervised clustering technique, which is adaptive and based on two criterion. In this context, the detected points are initially clustered based on the stable local features related to the brightness and color, which are extracted using Gabor filter. Then points belonging to each partition are reclustered depending on the dispersion of the points in the initial cluster using position feature. This two-step hierarchical clustering yields the possible candidate road signs or the region of interests (ROIs). Finally, a fringe-adjusted joint transform correlation (JTC) technique is used for matching the unknown signs with the existing known reference road signs stored in the database. The presented framework provides a novel way to detect a road sign from the natural scenes and the results demonstrate the efficacy of the proposed technique, which yields a very low false hit rate.

Cryptanalysis of an image encryption scheme based on joint transform correlator with amplitude- and phase- truncation approach

In this paper, a novel optical cryptosystem is proposed that uses amplitude- and phase-truncation approach in joint transform correlator (JTC) architecture. Due to amplitude- and phase- truncation, the encryption scheme becomes asymmetric and cryptanalysis of the scheme reveals that it is resistant to hybrid attack. This hybrid attack is the combination of specific attack on asymmetric cryptosystem and chosen-plaintext attack on JTC. We also carry out authentication verification using this correlation geometry. The scheme can be implemented digitally or optically employing a conventional JTC. Computer simulation results validate the proposed method.

Athermal Design of Infrared Telephoto Used in Joint Transform Correlator

On the basis of optical correlation detection, joint transform correlator(JTC) is widely used in military, aviation and intelligentization and so on. It has the advantages of great flexibility and high precision of recognition. The optical system is applied to receive the infrared radiation of the target. Athermalization is the key to stabilizing the optical performance with respect to off-design temperature. Therefore, the image quality of optical system in different temperatures plays an important role in JTC. In order to improve the environmental adaptability of JTC, the infrared telephoto system with high image quality and high performance-price ratio is designed for wavelength 8μm～12μm to detect target in a large range of temperature. This telephoto lens is composed of four refractive lenses. Three materials, zinc selenide, germanium and zinc sulfide are used to compensate for the temperature. The focal length is 200 mm, the relative aperture is 1:3, and the field of view is 6.4°. This system has the characteristics of small volume and compact structure. The optical system image quality is evaluated with ZEMAX optical design software. The results have shown that MTFs in the range of -40°C to +60°C are all closed to the diffraction limited curve. The spot diagram RMS radius of each field is closed to the Airy disk radius. The system meets the requirements of technical specification and improves the ability of JTC in target tracking and recognition.

Infrared Telephoto Design Used in Joint Transform Correlator

In order to meet the requirement of tank sight and improve the ability of Joint Transform Correlator(JTC) in target detection and recognition, the infrared telephoto system with high image quality and high performance-price ratio is designed for wavelength 8μm～12μm. Initial structure is composed of four refractive lenses. The focal length is 200 mm, the relative aperture is 1:2.6 and image field of view is 1 inch (CCD). Considering the fabrication process, production cost and other factors, the system structure is further improved. First the telephoto which is composed of four lenses is designed with normal spherical surface. Then on the basis of the original spherical structure, an aspheric surface is introduced. The optical system can be reduced into three lenses. The image quality of the whole system becomes much better. The optical system image quality is evaluated with ZEMAX optical design software. The result shows that MTF of each field is close to the diffraction-limited curve at the cut-off frequency 17lp/mm. The spot diagram RMS radiuses are smaller than the radius of Airy disk 25.35μm. The wave front aberrations for all the fields are less than 0.25λ. The telephoto can meet the requirement of target detection. Combining JTC with this infrared telephoto lens, the infrared target at longer distance can be detected and recognized.

Optical Correlation Recognition Research of Low Light Level Target Based on Lifting Wavelet Transform

Optical correlation technology is an important application in target recognition field, which can apply Joint Transform Correlator (JTC) to achieve target recognition. For the Low Light Level (LLL) target with low contrast and background noise interference, using optical correlation method may reduce the recognition ratio. In order to solve the problem, an effective algorithm-adaptive directional lifting based on wavelet transform (ADL) is used to process LLL target image. LLL image enhancement and target edge extraction are applied in this algorithm. Experimental results show that this algorithm can enhance the brightness of the correlation peaks and has the advantage of quick operation.

Optical image encryption based on joint fractional transform correlator architecture and digital holography

We present a hybrid configuration of joint transform correlator (JTC) and joint fractional transform correlator (JFTC) for encryption purpose. The original input is encoded in the joint fractional power spectrum distribution of JFTC. In our experimental arrangement, an additional random phase mask (master key) is holographically generated beforehand by a Mach–Zehnder interferometer with a JTC as the object arm. The fractional order of JFTC, together with the master key, can remarkably strengthen the safety level of encryption. Different from many previous digital-holography-based encryption schemes, the stability and alignment requirement for our system is not high, since the interferometric operation is only performed in the generation procedure of the master key. The advantages and feasibility of the proposed scheme have been verified by the experimental results. By combining with a multiplex technique, an application for multiple images encryption using the system is also given a detailed description.

利用附加密钥旋转在光学联合相关结构中实现多二值图像加密

利用附加密钥旋转在光学联合相关结构中实现多二值图像加密

Improved approach for target detection and recognition on optoelectronic hybrid joint transform correlator

A conventional joint transform correlator (JTC) often generates large correlation sidelobes as well as a large correlation peak width, strong zero-order peak, and low diffraction efficiency in target detection and recognition, which make the detection ability of JTC lower. To conquer these difficulties, firstly, a joint power spectrum (JPS) subtraction technique was proposed in Fourier plane, where power spectrum of reference image and power spectrum of object image are subtracted from the JPS before inverse Fourier-transform operation, it is evident that the improved JPS removes the zero-order term. Secondly, a fringe-adjusted filter (FAF) was presented to restrain sidelobes and noises. The revised JPS is multiplied by a FAF before the inverse Fourier-transform operation to obtain the cross-correlation peak. Computer simulations showed the improved method can markedly eliminate zero-order diffraction and effectively control the sidelobes and noises compared to traditional JTC, and then enhance the detection ability for JTC. Experimental results presented the sharp correlation peak and also demonstrated this approach effectiveness.