Binary Joint Transform Correlator Research Articles

Spectral band independent recognition in a differential binary joint transform correlator

Images of a target in a specific spectral band in general show no correlation with images of the same target in a different spectral band. Hence in a joint transform correlator (JTC) architecture, if the reference and input target are the images captured through a visible (e.g., charge-coupled device or CCD camera) and infrared (IR) detector, autocorrelation peaks are not obtained. This drawback has been overcome in this paper by the use of a CCD–IR fused image as the reference image. Daubechies wavelet transform, which produces the least root-mean-square (RMS) error in the fusion process in comparison to other wavelets, has been used for the purpose. A comparative analysis of the proposed idea has been carried out for the classical JTC (CJTC), binary JTC (BJTC) and differential binary JTC (DBJTC) algorithms. Since the DBJTC removes the dc completely and produces sharp correlation peaks compared to the other techniques, computer simulation and experimental results are shown for the proposed idea using DBJTC. The same fused reference image has also been used to identify multiple targets in a scene using DBJTC. Performance measures like correlation peak intensity (CPI), dc/ac and peak correlation energy (PCE) have been calculated as metrics of goodness for the proposed scheme.

Binary differential joint-transform correlator based on a ferroelectric-liquid-crystal electrically addressed spatial light modulator

We implement a binary differential joint-transform correlator for real-time single- and multiple-target recognition applications. In a real-time situation the input scene is captured using a CCD or thermal camera. The obtained joint power spectrum is first differentiated and then binarized. The subset median threshold method was used to get the threshold value for binarization. The binarized joint power spectrum is displayed over a ferroelectric-liquid-crystal spatial light modulator and is Fourier-transformed optically to obtain the correlation peaks. Differential processing of the joint power spectrum removes the zero-order spectra (dc) and hence improves the detection efficiency. Experiments taking single as well as multiple input images have been performed. The parameters for a performance measure have also been calculated. Single and multiple targets with added Gaussian noise have also been used to check the correlation outputs. Computer simulation and experimental results are presented.

Performance of binary joint transform correlator using linear combination threshold function

A linear combination threshold function, which is defined as the linear combination of input and reference power spectra, is proposed to binarize the joint power spectrum of a joint transform correlator (JTC). The performance of binary JTC depends on the linear combination coefficients of input and reference power spectra. This relationship is investigated and an optimal linear combination threshold function is determined to get a trade-off between some of performance criteria for character recognition. The theory analysis and verification by computer simulation are described. The proposed technique is also investigated by a hybrid optoelectronic system.

Illumination sensitivity of joint transform correlators using differential processing: computer simulation and experimental studies

Differential and binary differential joint-transform correlators are found to be associated with high tolerance to illumination variation of the reference and target. This makes them suitable for illumination-independent pattern recognition applications. Computer simulation results show that a tolerance limit as high as an amplitude ratio of 0.25 between the target and the reference image can be attained. As a refinement to the above mentioned techniques, we suggest the use of isotropic difference operators. We also present some experimental results for the differential type JTCs.

Experimental and simulation studies on the performance of binary and gray-valued joint transform correlators under poor illumination conditions and nonoverlapping background noise

The correlation performance of four different types of joint transform correlators (JTCs) is investigated in a noncooperative situation when the target image is cluttered with scene noise and present under poor illumination condition. Computer simulation and experimental re- sults are provided. Although the binary JTCs based on spatial- frequency-dependent threshold (SFDT), sliding-window local-median threshold (SWLMT) offer good correlation performance in poor target image illumination conditions their performance is affected in the pres- ence of background noise in the target image. The JTC based on modified-fringe-adjusted filter (MFAF) performs better in such a com- bined situation. © 1997 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(97)01307-X)

Experimental demonstration of a binary single-lens joint transform correlator using chirp-modulated inputs

This paper introduces the single-lens joint transform correlator (SLJTC). The SLJTC is a two-stage processor. The first stage computes the chirp-modulated joint power spectrum. The chirp-encoded joint power spectrum may be viewed as containing an amplitude-encoded lens function or Fresnel zone plate. The correlation output is in the focal plane of this zone plate. As in the chirp-modulated joint transform correlator (JTC), the output contains a single correlation peak. The SLJTC has been experimentally demonstrated with a peak-to-noise ratio (PNR) of 17.1 dB. The same chirp-encoded joint power spectrum used in the second stage of a binary chirp-modulated JTC resulted in 6.5-dB-poorer PNR performance.

Experimental comparison of binary joint transform correlators used for fingerprint identification

We compare the experimental performance of 12 variations of the binary joint transform correlator (BJTC) when used for fingerprint identification. Three hardware architectures were used: a single spatial light modulator (SLM) BJTC, a BJTC using two input SLMs, and a chirpencoded BJTC using two input SLMs. These correlators were implemented on the same hardware setup with minor modifications. With each hardware configuration, four binarization techniques were implemented: global threshold, Fourier plane windowing, frame subtraction, and frame subtraction followed by windowing. A set of 10 experiments was used to characterize the output peak intensity, peak-to-noise ratio, and discrimination ratio. The same set of experiments was run on each of the 12 correlator variants.

Cosine wave encoded joint transform correlation

University of SussexIndustrial Informatics & ManufacturingSystems Research CentreSchool of Engineering, ENGG1Brighton, United Kingdom BN1 9QTAbstract. A cosine wave encoded joint transform correlation is pro-posed that can deliver excellent correlation performance in the presenceof nonoverlapping noise or additive noise, and guarantee that the opticalgain is less than unity—facilitating implementation. The method pro-posed uses three CCDs to capture the power spectra of the joint image,the reference-only image, and the input scene, and then extracts thecosine wave information of the joint power spectrum using simple sub-traction and division operations. The extracted cosine wave informationis encoded onto the input SLM of the second optical setup, resulting in ahigh optical efficiency. The cosine wave encoded joint transform corre-lation is found to be similar to even-function correlations between thephase-only Fourier-plane information of the reference and input images,which resembles the correlation of the phase-only input scene informa-tion with the phase-only filter using a reference image in the VanderLugtcorrelation arrangement. Computer simulations show that the cosinewave encoded joint transform correlation outperforms binary joint trans-form correlation when the targets are embedded in either nonoverlap-ping noise or scenes with additive noise; performance is maintainedeven when the target has a very low light contrast ratio in a severelynoise-corrupted input scene. © 1996 Society of Photo-Optical Instru-mentation Engineers.

Performance of joint transform correlation under varying illumination and noise

The effect of varying the input scene illumination and noise on the performance of binary and fringe-adjusted joint transform correlators (JTCs) has been investigated in this paper. Simulation results show that the fringe-adjusted JTC yields superior correlation output when compared with the binary JTC for all types of input scenes affected by both illumination and noise. Furthermore, the binary JTC has been found to yield a good correlation output when zero mean, unity variance Gaussian white noise is added to input scenes affected by poor illumination.

Synthetic discriminant function fringe-adjusted joint transform correlator

A synthetic discriminant function (SDF) fringe-adjusted joint transform correlator is proposed that is able to provide a high degree of image distortion invariance and classify different objects in the input scene. The SDF reference function, which is displayed alongside the input scene, is a linear combination of the training image set. An iterative algorithm is presented and utilized to obtain the linear combination coefficients from the nonlinear equations of the fringe-adjusted joint transform correlation (JTC) system. When compared with the SDF-based classical JTC and binary JTC, the SDF fringe-adjusted JTC delivers a better capability to give localized equal correlation peak heights for the same class of objects. Furthermore, when the input scene contains the different objects from the different classes of images, the SDF fringe-adjusted JTC is shown to efficiently classify the different target objects and reject the nontarget object in the input scene, whereas the SDF-based classical JTC and binary JTC fail to achieve this.

Approximate performance of the nonlinear joint transform correlator in signallike noise

We present a statistical-analysis technique for a nonlinear joint transform correlator (JTC) based on two assumptions: the noise and the signal spectra are identical, and the signal energy is small relative to the noise energy. The first assumption, while admittedly convenient, is also defensible in that it is a worst case and in that image and scene noise can be similar in texture. The second is also reasonable, given that even a clearly visible signal may have small energy compared with the scene noise if it is of limited extent; in any case, the results appear moderately faithful even for the case that signal and noise energies are equal. We discover that the optimal Fourier-plane transformation is spatially variant and tends to remove the Fourier amplitudes of the input image, and indeed functions in a way very similar to the spatially variant binary JTC. We also see that the classic (or spatially invariant linear) JTC is a very inferior technique for signallike noise, that the best spatially variant binary JTC uses a threshold proportional to the noise power spectrum, and that, if a spatially invariant binary-thresholded JTC is desired, then the median Fourier-plane value is an excellent choice of threshold. The performance predictions are verified by simulation and appear to be reasonable even for the highly nonlinear binary schemes.

Fourier-plane windowing in the binary joint transform correlator for multiple target detection

With recent advances in state-of-the-art spatial light modulators, the optical joint transform correlator (JTC) and the binary joint transform correlator (BJTC) are becoming practical signal-processing tools. The performance of these devices is limited by the difficulty of separating the cross correlation between the reference and the targets in the scene from signals resulting from cross correlations between objects in the target scene. One technique that reduces this problem is to use a sliding window in the Fourier plane as a convolution mask filter to set an adaptive binarization threshold. This suppresses the autocorrelation response and reduces the dynamic range of the Fourier-plane signal. This results in correlation performance improvement by a factor of 2 to 4. A mathematical model is developed to describe the windowing process for both the JTC and BJTC for the case in which the scene contains multiple targets and background clutter. The derivation of the windowing process is general and includes any spatial high-pass or bandpass filtering in the Fourier plane. The results are supported with experimental data.

Multiobject detection using the binary joint transform correlator with different types of thresholding methods

The correlation performance of the binary joint transform correlator for multiobject detection is studied mathematically and experimentally using three types of thresholding methods. These thresholding methods include the spatial frequency dependent threshold function, the median thresholding, and the subset median thresholding. We provide a new expression for the image separation requirement in the input plane of the linear joint transform correlator for multiobject detection. Also, we introduce a new analytical approach for obtaining the threshold function in the binary joint transform correlator. The median thresholding method for multiobject detection by the binary joint transform correlator (JTC) is also analyzed. A hybrid optoelectronic setup is used for experiments. Two different implementations of the threshold function are employed in the experimental system. Experimental results of the binary JTC using different thresholding methods are determined and compared in terms of correlation peak-to-noise ratio, peak-to-sidelobe ratio, and space-bandwidth product. The results indicate that the binary JTC performs well for multiobject detection. Furthermore, using the threshold function in the binary JTC eliminates the first-order correlations between different input targets and the even-order harmonic terms in the output plane.

Applying time modulation to the joint transform correlator

A major limitation on the optical joint transform correlator (JTC) is that the output plane is dominated by unwanted autocorrelation products. A new technique is proposed that uses time modulation and demodulation to separate the correlation components. Time modulation is applied to the JIG inputs, resulting in a time-modulated joint power spectrum. Demodulation of the transform plane separates the self-correlation components from the other terms. When the demodulated signal is the input to the second transform stage in the JTC the result is system peak-to-noise ratio/peak-to-secondary ratio (PNR/PSR) improvement, removal of input plane location constraints, and elimination of detection problems resulting from multiple targets. Two implementations are discussed. Using a general model for sinusoidal modulation, it is shown that amplitude, phase, and polarization modulation of the inputs all result in amplitude modulation of the correlation signals in the transform plane. The general solution is difficult to implement, because it requires temporal demodulation of the joint Fourier signal on a pixel-by-pixel basis. A more practical system results from the case of square-wave modulation, where it is shown that demodulation can be easily implemented through image subtraction using only two to four frames of data. This Fourier plane processing technique has been implemented using a binary JTC (BJTC). Performance improvement of 6 dB over the conventional BJTC is demonstrated through computer simulation and laboratory results.

Fringe-adjusted joint transform correlation

Improved correlation discrimination is achieved by using a fringe-adjusted joint transform correlator (JTC). This technique is found to yield significantly better correlation output than the classical and binary JTC's for input scenes involving single as well as multiple objects. It also avoids the computation-intensive Fourier-plane joint power spectrum binarization processing of a binary JTC. Two optical implementations for the proposed technique are also suggested.

Joint-transform correlation under varying illumination

The effect of varying the illumination of the target scene on the performance of classical, binary, and fringe-adjusted joint-transform correlators is investigated. Simulation results show that the fringeadjusted joint-transform correlator yields better correlation output than the classical or the binary joint-transform correlator under all illumination conditions of the target scene.

Preprocessed multiobject joint transform correlator

The performance of a joint transform correlator (JTC) in a multiobject environment is improved by the use of a Roberts operator to preprocess the input joint image. This technique yields significantly better results than the classical JTC, and it also avoids the false alarms and reduces the overall computation overhead required in a binary JTC.

Enhanced correlation discrimination using binary joint transform correlation with feedback

AbstractThe correlation peak intensity in a binary joint transform correlator (JTC) usually decreases as the number of objects in the input scene increases. This problem is solved by incorporating additive feedback in a binary JTC to update the input plane information on the basis of correlation plane information. © 1992 John Wiley & Sons, Inc.

Multiple-object binary joint transform correlation using multiple-level threshold crossing

We investigate the performance of the binary joint transform correlator (JTC) in the presence of multiple objects for two types of thresholding that are used to binarize the joint power spectrum. The first method uses the median of the joint power spectrum of the reference image and the input scene as the threshold value. The second method is a two-dimensional thresholding technique used to maximize the light intensity of the correlation peak, and it eliminates the even-order harmonic terms. The correlation performance of the binary JTC is determined for both thresholding methods. The binary JTC output is determined analytically in terms of multiple input targets. The separation requirements of the binary JTC and the conventional JTC in the presence of multiple targets are computed. Computer simulation and experiments are presented for a limited number of multiple-target images to determine the correlation peak-to-sidelobe ratio and the correlation width for both thresholding techniques. In the experiments, a hybrid optical processor with an optically addressed spatial light modulator is used to implement the binary JTC. The results indicate that, using both thresholding methods, the binary JTC produces a large peak-to-sidelobe ratio and a narrow peak for the multiple-target images used in the tests. The two-dimensional threshold function produces better correlation performance compared with the median thresholding.

Quantization and truncation effects on binary joint transform correlation

Analysis of the quantization effects of the binarized joint power spectrum on the performance of the binary joint transform correlator (JTC) is investigated. The signal to noise ratio (SNR) of the binarized joint power spectrum is determined for various levels of the Fourier plane quantization of the binary JTC. The SNR is computed for the truncated binarized joint power spectrum plane and the binary JTC performance is determined for various levels of Fourier plane truncation. Analytical expression are derived for the capture effect of the binary JTC in the presence of the Fourier plane quantization. Nonlinear compression or truncation in the Fourier plane can improve the performance of the binary JTC at low quantization levels. Computer simulation is used to verify the results of the theoretical analysis.