Bahram Javidi

Joint transform image correlation using a binary spatial light modulator at the Fourier plane.

The present invention is a nonlinear joint transform image correlator which employs a spatial modulator operating in a binary mode at the Fourier plane. The reference and input images are illuminated by a coherent light at the object plane of a Fourier transform lens system. A image detection device, such as a charge coupled device, is disposed at the Fourier plane of this Fourier transform lens system. A thresholding network detects the median intensity level of the imaging cells of the charge coupled device at the Fourier plane and binarizes the Fourier transform interference intensity. The correlation output is formed by an inverse Fourier transform of this binarized Fourier transform interference intensity. In the preferred embodiment this is achieved via a second Fourier transform lens system. This binary data is then applied to spatial light modulator device operating in a binary mode located at the object plane of a second Fourier transform lens system. This binary mode spatial light modulator device is illuminated by coherent light producing the correlation output at the Fourier plane of the second Fourier transform lens system. The inverse Fourier transform may also be formed via a computer. In an alternative embodiment, the Fourier transform interference intensity is thresholded into one of three ranges. An inverse Fourier transform of this trinary Fourier transform interference intensity produces the correlation output.

Multiple Object Identification By Bipolar Joint Transform Correlation

We investigate the performance of a recently introduced bipolar joint transform image correlator when multiple reference objects and single and multiple targets are present at the input plane. The bipolar joint transform correlator uses nonlinearity at the Fourier plane to threshold the Fourier trans-forms interference intensity to only two values, 1 and -1. The performance of the bipolar correlator is compared to the classical joint transform image correlator when multiple objects are present at the input plane. We show that the performance of the bipolar correlator is substantially superior to that of the classical joint transform image correlator in the areas of autocorrelation peak intensity, autocorrelation peak to sidelobe ratio, autocorrelation bandwidth, and discrimination sensitivity. It is shown that when multiple objects are present at the input plane, the classical joint transform image correlator produces large cross-correlation signals and poorly defined autocorrelation signals with large bandwidth. The large cross-correlation signals are comparable in intensity with the autocorrelation peak and can falsely indicate the presence of many targets. On the other hand, the bipolar joint transform image correlator produces well-defined autocorrelation signals with very low cross-correlation level. Computer simulations are used to test both types of correlators, and 3-D plots of the correlation functions are provided and discussed.

Rotation and scale sensitivities of the binary phase-only filter

Abstract The scaling and rotation sensitivity of a bianary phase-only correlator is studied and compared to that of continuous phase-only correlator, classical correlator, and edge-enhanced classical correlator. Computer simulation of the optical system is used to determine values of the correlation peak intensity versus scale and rotation changes of the input signal for the four filter types. The results show that the binary phase-only filter is slightly less sensitive to such input variations than is the continuous phase-only filter.

Color object identification by monochromatic binary correlation

A real-time polychromatic image correlator that uses a magnetooptic (MO) spatial light modulator (SLM) device for pattern recognition based on both the color and shape of an input object is presented. The proposed system utilizes a multichannel spectral matched spatial filter employed in a binary coherent optical correlator. Input color images are transformed into binary color coded coherent images by a color grating. The color encoded images are read out by a charge coupled device interfaced with a MO SLM. The color encoded binary images are then processed by a multichannel joint spectral matched spatial filter synthesized by monochromatic light. Pattern recognition experiments for naturally illuminated real color objects are presented.

Comparison Of Bipolar Joint Transform Image Correlators And Phase-Only Matched Filter Correlators

In this paper, we compare the performance of the bipolar joint transform correlator to the continuous phase-only matched filter correlator, the binary phase-only matched filter correlator, and the classical correlator. The pattern recognition systems will be compared in the areas of correlation peak, autocorrelation peak to sidelobe ratio, autocorrelation bandwidth, and discrimination sensitivity.

Deconvolution using nonlinear joint transform correlator

Abstract The joint transform optical processor has always been used for correlating two signals. We show how it can be used for deconvolution and image restoration. Through computer simulation we show specifically how to use this architecture to restore a linearly smeared image.

Analysis of a partially coherent optical correlator in the presence of phase defects at the input plane

Abstract The effects of phase defects at the input plane of an optical correlator on the performance of the system under partially coherent illumination is investigated. The correlation signal-to-noise ratio (SNR) is evaluated as the criterion for the performance of the optical system. We study the effects of both spatially and temporally partially coherent illumination on the distorted correlation signal. It is shown that the output SNR can be increased by relaxing the coherence requirements of the system. The SNR dependence on noise variation is also investigated. It is found that the correlator becomes less sensitive to noise variations under partially coherent illumination.

Comparison Of Bipolar Nonlinear Correlators And Phase-Only Encoded Matched Filter Correlators

In this paper, we compare the performance of the bipolar joint transform correlator to the continuous phase-only matched filter correlator, the binary phase-only matched filter correlator, and the classical correlator. The pattern recognition systems will be compared in the areas of correlation peak, autocorrelation peak to sidelobe ratio, autocorrelation bandwidth, and discrimination sensitivity.

Performance Of A Bipolar Nonlinear Correlator

A joint Fourier transform image correlator that uses a binary spatial light modulator at the Fourier plane is presented. In this system, the Fourier transforms interference intensity is thresholded to only two values so that a binary spatial light modulator can be used to read-out the interference intensity. The performance of the correlator introduced here is compared to the classical joint transform correlator in the following areas: correlation peak, correlation peak to sidelobe ratio, correlation bandwidth, and discrimination. We show that the bipolar Fourier transforms interference intensity can result in a higher correlation intensity and a better defined correlation spot than the classical joint transform correlator. Computer simulation is used to test the correlators and the three dimensional plots of the autocorrelation and cross-correlation functions are presented and discussed.

Industrial Applications Of Optical Signal Processing I

Optical technology has emerged as a viable solution to the growing demand to increase the throughput of high speed processors and computers. Although higher speed and denser integrated circuits are being developed, it appears that faster switching speeds in digital circuits will not provide an adequate solution to the bottleneck problem of computing systems for such tasks as real-time distortion-invariant pattern recognition and associative memory. Even supercomputers using new computing architectures and subnanosecond gate delays do not have sufficient speed for such real-time operations. Optical systems offer the advantages of inherent parallelism and high speed with superior interconnection capability, which allow for the processing of millions of simultaneous operations. The lack of electromagnetic interference in optics is ideally suited for neural network based proces-sors, which require a high degree of interconnectivity and global communications properties. Analog optical computers are particularly attractive for the processing of large stochastic data, while the more precise digital computers break down when confronted with such random problems. The immunity to electromagnetic interference can also be used advantageously in VLSI interconnections technology and board-to-board communications to reduce the pinout problem and to improve flexibility and performance. For these reasons, optical technology has become a major research and development effort at many industrial, government, and university laboratories both nationally and internationally.