Joint Transform Correlator System Research Articles

Deblurring for spatial and temporal varying motion with optical computing

A way to estimate and remove spatially and temporally varying motion blur is proposed, which is based on an optical computing system. The translation and rotation motion can be independently estimated from the joint transform correlator (JTC) system without iterative optimization. The inspiration comes from the fact that the JTC system is immune to rotation motion in a Cartesian coordinate system. The work scheme of the JTC system is designed to keep switching between the Cartesian coordinate system and polar coordinate system in different time intervals with the ping-pang handover. In the ping interval, the JTC system works in the Cartesian coordinate system to obtain a translation motion vector with optical computing speed. In the pang interval, the JTC system works in the polar coordinate system. The rotation motion is transformed to the translation motion through coordinate transformation. Then the rotation motion vector can also be obtained from JTC instantaneously. To deal with continuous spatially variant motion blur, submotion vectors based on the projective motion path blur model are proposed. The submotion vectors model is more effective and accurate at modeling spatially variant motion blur than conventional methods. The simulation and real experiment results demonstrate its overall effectiveness.

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.

Binary phase only filters for rotation and scale invariant pattern recognition with the joint transform correlator

The joint transform correlator (JTC) is one of the two main optical image processing architecture which provides a highly effective way of comparing images in a wide range of applications. Traditionally, an optical correlator is used to compare an unknown input scene with a pre-captured reference image library, to detect if the reference occurs within the input. Strength of the correlation signal decreases rapidly as the input object rotates or varies in scale relative to the reference object. The aim of this paper is to overcome the intolerance of the JTC to rotation and scale changes in the target image. Many JTC systems are constructed with the use of ferroelectric liquid crystal (FLC) spatial light modulators (SLMs) as they provide fast two-dimensional binary modulation of coherent light. Due to the binary nature of the FLC SLMs used in the JTC systems, any image addressed to the device need to have some form of thresholding. Carefully thresholding the grey scale input plane and the joint power spectrum (JPS) has significant effect on the quality of correlation peaks and zero order (DC) noise. A new thresholding technique to binarise the JPS has been developed and implemented optically. This algorithm selectively enhances the desirable fringes in the JPS which provide correlation peaks of higher intensity. Zero order noise is further reduced when compared to existing thresholding techniques. Keeping in mind the architecture of the JTC and limitations of FLC SLMs, a new technique to design rotation and scale invariant binary phase only filters for the JTC architecture is presented. Filers design with this technique have limited dynamic range, higher discriminability among target and non-target objects, and convenience for implementation on FLC SLMs. Simulation and experiments shows excellent results of various rotation and scale invariant filters designed with this technique. A rotation invariant filter is needed for various machine vision applications of the JTC. By fixing the distance between camera and input object, the scale sensitivity of the correlator can be avoided. In contrast to the industrial machine vision applications, scale factor is very important factor for the applications of the JTC systems in defence and security. A security system using a scale invariant JTC will be able to detect a target object well in advance and will provide more time to take a decision.

Novel real-time joint-transform correlation by use of acousto-optic heterodyning.

To replace the film recording aspect of performing optical correlation, conventional real-time joint-transform correlation (JTC) optical systems make use of a spatial light modulator (SLM) located in the Fourier plane to record the joint-transform power spectrum (JPS) to achieve real-time processing. The use of an SLM in the Fourier plane, however, is a major drawback in these systems because SLMs are limited in resolution, phase uniformity, and contrast ratio, which are, therefore, not desirable for robust applications. We propose a hybrid (optical/electronic) processing technique to achieve real-time joint-transform correlation. The technique employs acousto-optic heterodyning scanning. The proposed real-time JTC system does not require an SLM at the Fourier plane as in other real-time JTC systems. This departure from the conventional scheme is extremely important as the proposed approach does not depend on SLM issues. We develop the theory of the technique and substantiate it with experimental results.

가상 영상을 이용한 주파수 영역에서의 광학적 암호화 및 복호화 방법

본 논문에서는 위상 변조된 가상 영상과 결합변환상관기를 이용하여 암호화 및 복호화 수준을 향상시키는 방법을 제안하였다. 원 영상은 주파수 영역에서 가상 위상 영상과 무작위 위상 영상의 곱을 퓨리에 변환하여 만든 암호화 영상과 제안한 위상 대응 규칙으로 만든 퓨리에 복호화 키를 퓨리에 변환하여 출력 평면에서 간단히 복원된다. 제안한 방법은 암호화된 영상을 허가되지 않은 사람들이 분석함으로써 있을 수 있는 복제 가능성을 원 영상의 어떤 정보도 포함하지 않은 가상 영상을 사용함으로써 배제할 수 있다. 또한 위상 변조된 영상의 자기상관성분의 세기는 1이므로 원 영상은 이 자기상관성분을 이용하여 재생되므로 결합변환상관기의 가장 큰 문제점인 자기상관성분을 제거해야 하는 문제를 해결할 수 있다 하지만 위상 암호화방법은 잡음이나 흠집에 민감하여 복원영상의 왜곡이 발생할 수 있으므로 본 논문에서는 이 문제를 분석하고 해결책을 제시하였다. 검증 실험을 통하여 분석의 타당성을 확인하고 제안한 암호화 방법이 광 암호화 시스템에 적용 가능함을 확인하였다. In this paper, we propose an improved image encryption and decryption method using a virtual image and a joint transform correlator (JTC). The encrypted image is obtained by the Fourier transform of the product of a virtual-phase image and a random-phase image, and a Fourier transform of the decrypting key generated by the proposed phase assignment rule is used as the Fourier decrypting key. Based on the solution, the original image is reconstructed using JTC in the frequency-domain. The proposed method using a virtual image, which does not contain any information from the original image, prevents the possibility of counterfeiting by unauthorized people. And also the auto-correlation terms, which are the drawback of a JTC system, contribute to reconstructing the original image rather than to disturbing its identification. But because phase-only encryptions are sensitive to noise and scratches, phase errors can be generated in fabricating the encrypted image or the Fourier decrypting key so the errors that are responsible for degradation of the quality of the reconstructed image are analyzed and the solution is demonstrated. Computer simulations show the solution, and the proposed method is very useful for JTC architecture.

Color pattern recognition in white-light joint transform correlation

We first discuss the restriction on the incoherent source and the color filters in a joint transform correlation (JTC) system for white-light color pattern recognition and then report on a novel, to our knowledge, solution of channeling in a white-light JTC system, using a tricolor grating to encode the color patterns in real time. The theoretical analyses and the experimental results show not only that the restriction on the experimental condition is relieved but also that parallel channeling of the power spectra of the encoded pattern is easily performed. In addition, the zero-order power spectrum also forms a useful channel for the shape-only correlation.

Development of an optical joint transform correlation system for fingerprint recognition

Yuji KobayashiHaruyoshi ToyodaCentral Research LaboratoryHamamatsu Photonics K.K.5000, Hirakuchi, HamakitaShizuoka 434-8601, JapanE-mail: kobayasi@crl.hpk.co.jp,toyoda@crl.hpk.co.jpAbstract. A compact joint transform correlator is designed and con-structed to test the properties of a practical application and is applied tofingerprint recognition. The system performance is evaluated on finger-print recognition accuracy under thermal conditions ranging from 0 to40°C and is found to provide a high level of identification and rapidprocessing abilities under actual environmental conditions.

Parallel joint transform correlator applied to Devanagari script recognition

A novel, to our knowledge, scheme for a parallel joint transform correlator system is demonstrated by the introduction of a five-channel zone-plate image multiplicator combined with photographic referencing and is applied to the recognition of Devanagari script. For considering the script's specific features, a partial image was obtained by means of windowing with 25 x 25 pixels out of a 64 x 64 pixel image of full-size characters and was employed for correlation. A comprehensive measurement of all 38 fundamental characters, namely, 1444 correlation pairs, showed satisfactory discrimination performance.

Influence of flatness distortion on the output of a liquid-crystal-television-based joint transform correlator system

The use of liquid-crystal panels from a commercially available Sanyo video projector as spatial light modulators in a standard joint transform correlator system is investigated. It is found that the flatness distortion of the panels disturbs the output correlation signal in general. Since the reported solutions for the flatness corrections are either expensive (liquid gates) or suffer from low light efficiency (holographic techniques), we have investigated a possibility to minimize the influence of these distortions on the correlation output without flatness correction. First, we quantify optical flatness across the transparent panel area, and then we measure the effects of flatness distortion by changing the display location of the input objects and the resulting joint power spectrum. It is found that the correlation peak is 1 order of magnitude more sensitive to phase distortions of the input scene than to the same distortions of the joint power spectrum. Choosing the flattest location on the panel allows the utilization of the panels to be demonstrated through recognition of cuneiform inscription signs.

High-efficiency hybrid joint transform correlator with pre-processed input image and replicated binary spectrum array

The performance of a hybrid joint transform correlator (JTC) is improved by the input image pre-processing method and our proposed spectrum binarizing and replicating technique. The input image pre-processing can enhance the correlation discrimination ability of a JTC system, and the replication of the binary spectrum under an appropriate condition can further substantially increase the light efficiency, the maximum correlation peak intensity, the peak sharpness and the signal-to-noise ratio of the system at the same time by the mechanics of constructive interference. Theoretical analyses are presented. Both the computer simulation and optical experiment verifying the effectiveness of this technique are also given.

Real-time demonstration of an on-board nonlinear joint transform correlator system

We design, implement, and test an optical joint transform cor- relator, using a nonlinear optically addressed ferroelectric liquid-crystal spatial light modulator in the Fourier plane. This compact correlator per- forms real-time and on-board recognition tasks. Results of in-car experi- ments for road sign recognition in real environments are presented. © 1997 Society of Photo-Optical Instrumentation Engineers.

Fingerprint identification by an optical joint transform correlation system

An optical correlator has been used in fingerprint identification, and in order to test its properties in a practical application a compact joint transform correlation system was constructed. The system’s identification performance was qualitatively and statistically evaluated, based on fingerprint data gathered from 500 fellow workers. The power of parallelism and fast processing of optical processing enabled the system to verify an individual’s identity in less than 0.1 s on each try. The system performed a verification with a 4.1% false rejection rate and no false acceptance in “three-try.”

Construction and Evaluation of a Visible Spectrometer Using Digital Micromirror Spatial Light Modulation

Digital micromirror devices (DMDs), also known as spatial light modulators, have been produced in a wide variety of configurations specific to their applications such as joint-transform correlator systems, optical neural networks, and high-definition televisions. The characteristics of DMD technology and flexibility of design lend themselves to a new application in optical spectrometers. Medium-resolution optical spectrometers, with a spectral bandwidth on the order of 1 nm, are widely used in instrumentation designed to record molecular absorption spectra in the ultraviolet and visible regions and are among the most widely used laboratory instruments. Modern UV-visible spectrometers usually are designed to use a multichannel detector, such as a photodiode array (PDA), in conjunction with a compact fixed-resolution spectrograph and can record spectra with reasonable speed, ∼ 30 ms. These spectrographs have no moving parts and are used for on-line detection of chromatographic eluents, for routine analytical determinations, and for industrial applications such as measurements made in process streams. However, diode array detectors are generally more expensive and are less sensitive than photomultiplier tubes (PMTs), particularly in the UV, and require cooling when a long integration time and low dark current are necessary. In addition, the diode array cannot acquire spectra fast enough for most kinetic studies to be made. A medium-resolution spectrometer which incorporates DMD technology and a PMT for detection has the potential of obtaining a spectrum on the order of a few milliseconds with high sensitivity at a lower cost than that for current PDA or charged-coupled device (CCD) spectrometers. Another advantage of the DMD spectrometer is that it possesses the capability of repetitively scanning a small portion of the spectrum without collecting the entire spectrum (random pixel access). The high sensitivity of a DMD spectrometer using a PMT also makes it ideal for fluorescence and phosphorescence detection.

Matched filtering incorporating colored-noise compensation for joint transform correlators

Optimal recognition of patterns with respect to noise tolerance is obtained when matched filtering is applied with colored-noise compensation, for which input-noise spectral characteristics have to be known in advance. Conventional joint transform correlator systems provide such optimality only when the input noise is white. We propose general means to facilitate colored-noise tolerance by incorporating either a priori or adaptive noise compensation in joint transform correlator-based matched filtering schemes. Adaptive compensation for colored noise may be achieved in real-time operation by estimation of the noise power spectral density distribution from input power spectra information.

Polychromatic target identification with a color liquid-crystal-TV-based joint-transform correlator

A real-time polychromatic target-detection technique that uses a computer-addressable color liquid-crystal- TV-based joint-transform correlator (JTC) is presented. One of the major features of the polychromatic JTC is that the spectra content of the object can be exploited. Since the liquid-crystal-TV panel is computer addressable, the JTC system can be made adaptive, by which the joint-transform power spectrum can be manipulated. Experimental demonstration of the proposed polychromatic JTC is provided, in which we show that the spatial and the spectral content of targets can be detected.

Matched, phase-only, or inverse filtering with joint-transform correlators

We show that configurations based on joint-power-spectrum correlators can provide not only classical matched filtering but also phase-only or inverse filtering. General, simple, and powerful means that extend the capabilities of classical joint-transform correlator systems are proposed. Moreover, inverse filtering with joint-transform correlators exhibits not only high peak sharpness but also high light efficiency, unlike inverse filtering with frequency–plane correlators, for which these two quantities are inversely related.

Joint transform correlator that uses wavelet transforms

A joint transform correlation system based on wavelet transforms is introduced. The selection of wavelets and the optical wavelet transform of images enables this optical correlator to identify the specific features and distinguish similar characters. Preliminary experimental results are given.

Data association multiple target tracking using a phase-mostly liquid crystal television

This paper presents a technique of using data association target tracking in a motion sequence via an adaptive joint transform correlator. The massive data in the field of view can be reduced to a few correlation peaks. The average velocity of a target during the tracking cycle is then determined from the location of the correlation peak. We have used a data association algorithm for the analysis of these correlation signals, with which multiple targets can be tracked. A phase-mostly LCTV is used in the hybrid joint transform correlation system, and simultaneous tracking of three targets is demonstrated.

Joint-transform correlator systems using deformable-mirror spatial light modulators

Two joint-transform correlator systems based on deformable-mirror-device (DMD) spatial light modulators and charge-coupled-device (CCD) video cameras are described. The system designs provide for real-time correlation between video-formatted input scenes and stored reference images. The DMD light modulators are used exclusively for inputting data in the optical stages of these systems, and the CCD cameras are used to provide the critical square-law detection required in joint-transform architectures. Experimental verification of the functionality of these DMD/CCD joint-transform systems is also presented.