VanderLugt Correlator Research Articles

Combined optical and neural network fingerprint matching

This paper presents results on direct optical matching of inked and real-time fingerprint images. Direct optical correlations and hybrid optical neural network correlation are used in the matching system for inked fingerprints. Preliminary results on optical matching of real-time fingerprints use optical correlation. The test samples used in the inked image experiments are the fingerprint taken from NIST database SD-9. These images, in both binary and gray level forms, are stored in a VanderLugt correlator. Tests of typical cross correlations and auto correlation sensitivity for both binary and 8 bit gray images are presented. When global correlations are tested on a second inked image results are found to be strongly influenced by plastic distortion of the finger. When the correlations are used to generate features that are localized to parts of each fingerprint and combined using a neural network classification network and separate class-by-class matching networks, 84.3 percent matching accuracy is obtained on a test set of 100,000 image pairs. Initial results with real- time images suggest that the difficulties resulting from finger deformation can be avoided by combining many different distorted images when the hologram is constructed in the correlator. Testing this process will require analysis of 10-20 second sequences of digital video.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Control of a VanderLugt correlator using a single 8-bit frame grabber

We analyze in depth several engineering problems regarding the construction of a VanderLugt correlator. Two liquid crystal devices are used in the input and Fourier planes, and the large distances involved are reduced with the help of telephoto systems. An original method to control both modulators with a single 8-bit frame grabber and a single videoprojector electronics is presented. Problems related to pixel-by-pixel addressing and the phase modulation in the panels are also discussed. All the solutions proposed in this paper have been implemented and experimental correlation results using the setup have been obtained.

Real-Time Shift-Invariant Optical Pattern Recognition

Shift invariance is an asset of the VanderLugt correlator, from which the location of the identified object is automatically specified. The development of filters which possess two or three types of invariance (shift, rotation, size, and distortion) simultaneously is reviewed. Various real-time implementation of VanderLugt as well as joint-transform correlators by utilizing spatial light modulators are also reviewed.

Robustness of joint transform correlator versus VanderLugt correlator

The robustness of the joint transform correlator (JTC) versus the VanderLugt correlator (VLC) are evaluated based on the transversal and the longitudinal misalignment. We show that the VLC is very sensitive to the transversal misalignment, while the JTC is not. Although the VLC performs better in terms of longitudinal alignment, the tolerable misalignment in recording the joint transform power spectrum (JTPS) is in the order of a millimeter, which can be easily adjusted in practice. In short, we conclude that the JTC is far more robust than the VLC.

Real-time pattern recognition by vanderlugt correlator using amplitude and phase modulation properties of the epson Liquid-Crystal TV

We have built an optical VanderLugt-type correlator that uses two Epson liquid crystal televisions (LCTVs) separately generating the amplitude and phase modulation properties. The input scene is displayed in amplitudemostly regime on the first LCTV. Thereafter a phase-only filter with a different level of phase quantization is addressed in phase-mostly regime on the second LCTV. To characterize this device, the phase and amplitude modulations were experimentally measured and investigated in pattern recognition application where the grey-level input scenes and multilevel kinoforms are displayed on the LCTVs.

Hybrid optical implementation of discrete wavelet transforms: a tutorial

Recently, there has been a great deal of interest in the use of wavelets to supplement or replace traditional Fourier transform signal processing. Because wavelet operations can be expressed as either a convolution/correlation operation or ā linear filter bank, they are well suited to optical implementations. This paper provides a tutorial on wavelets and the hybrid optical implementation of discrete wavelet transforms. Various approaches for implementing the wavelet transform are reviewed, including traditional Vander Lugt correlators, different types of spatial light modulators, joint time-frequency representations, holographic and interferometric implementations, and acousto-optic correlators. Finally, the concept for a new architecture is proposed using acousto-optic finite impulse response (FIR) filters to implement wavelets with perfect reconstruction properties.

A multichannel joint transform correlator

Optical correlation has profited from simultaneous advances in spatial light modulators and algorithms, which have considerably broadened its field of applications. Nevertheless, in many image processing tasks, multiple correlations are required. Optical multichannel correlation architectures have been proposed in the case of classical Vander Lugt correlators. We suggest a solution based on the joint transform correlator architecture. We show that this solution is well suited to the use of silicon backplane spatial light modulators involving variable pixel fill factor designs.

Spherical particle sizing based on the VanderLugt correlator

We present a flexible architecture for particle sizing based on the VanderLugt correlator with a multiplexed matched spatial filter. Theoretical and experimenal data obtained using opaque spherical particle projections demonstrate the potential uses and simplicity of the architecture. The system is capable of handling spherical and nonspherical particles and shows potential for handling high particle concentrations.

Space-variant Characteristics in Multiple Object Recognition with a Coherent Optical Processor

Abstract When the input plane of a Van der Lugt correlator contains a composite object, the output plane will in general contain several correlation peaks. When these correlation peaks overlap, the total intensity will be given by the coherent addition of the amplitudes of the individual peaks. It is shown in this paper that the total intensity depends on the phase difference between the correlation signals. The phase differences are dependent both on the displacement of the input object and any aberration in the correlator. A theoretical analysis of the system is given, showing that the interference between the correlation signals causes the total correlation intensity to change with object displacement in an oscillatory fashion rather than in a monotonic way. Some experimental verification of the theoretical predictions is also presented.

Comparison of vander lugt and joint transform correlators

A generalized optical correlator is used to analyze the performances of the Vander Lugt and the joint transform architectures. Noise performance and the effects caused by the differences between the input and the reference functions are analyzed. It is found that the modulation index of the joint transform filter decreases due to the presence of noise as well as the differences between the input and the reference functions. However, it is found that, in general, the joint transform correlator would perform better than the Vander Lugt correlator and certainly has the advantage for real-time implementation.

Comparison of detection efficiencies for VanderLugt and joint transform correlators

The correlation of peak intensities of VanderLugt and joint transform correlators with a single object, multiple objects, and noisy environments are analyzed. The study shows that the VanderLugt correlator can generally perform better for the multiple object case and also under a noisy environment.

Scale and projection invariant pattern recognition

A logarithmic-logarithmic coordinate transformation is used to perform successfully scale and projection (tilt) invariant optical pattern recognition. The coordinate transformation is achieved optically using a computer generated hologram divided into four different quadrants since the logarithmic function does not exist for negative values of the argument. The transformed pattern is introduced into a VanderLugt correlator setup through a liquid crystal light valve. Initial experimental results are presented.

Real time optical correlator architectures using a deformable mirror spatial light modulator

The recent production of a deformable mirror device (DMD) spatial light modulator has naturally led to techniques of using this device in popular optical correlator architectures. In this paper, the DMD is used in both joint transform and VanderLugt arrangements. In some cases, the DMD is used as the input device to a single stage joint transform correlator, and in other cases it is used as the filter device in a VanderLugt correlator. A liquid crystal TV is also used for real time addressing of filters displayed on the DMD.

Interference filters as nonlinear decision-making elements for three-spot pattern recognition and associative memories

Simple patterns consisting of three spots (V and Gamma) have been recognized by dividing, shifting, and recombining beams onto bistable ZnS interference filters. This experiment demonstrates AND-gate operation, cascading, and a moderate amount of parallelism, but a laser power of several watts was required and the response times were several milliseconds. An associative memory for fingerprint identification has been constructed using a VanderLugt correlator and an interference filter as a reflective thresholding device.

Optical Associative Memory Using Fourier Transform Holograms

An experimental demonstration of a holographic associative memory is presented. The system utilizes an array of classic VanderLugt correlators to implement in parallel the inner product between an input and a set of stored reference images. Each inner product is used to read out an associated image. Theoretical analysis of the system is given, and experimental results are shown.

Sensitivity of the VanderLugt correlation technique: application to grating period change measurements

The VanderLugt spatial frequency correlation technique for detecting changes in the grating period is analyzed numerically. A proposal for real-time quantitative measurement of the surface effects caused by events, such as diffusion or magnetostriction, is also discussed. Normalized correlation intensity peak values, presented as sensitivity curves, were computed for various grating parameters and several types of grating profile. Results indicated that a number of sensitivity curves describe the same change in the grating period, and the technique was found to be essentially profile independent.

Fresnel pseudocorrelator

A new type of optical device capable of signal identification is presented in this paper. The device is based on Fresnel holography, therefore it is called Fresnel pseudocorrelator. This pseudocorrelator has been examined by discerning between binary signals of printed letters. The results of signal identification obtained in the Fresnel pseudocorrelator are compared quantitatively with those obtained in a Van der Lugt correlator.

Optical Image Correlation With A Binary Spatial Light Modulator

The use of a binary, magneto-optic spatial light modulator as an input device and as a spatial filter in a VanderLugt correlator is investigated. The statistics of the correlation that is obtained when the input image or the spatial filter is thresholded are estimated. Optical correlation using the magneto-optic device at the input and Fourier planes of a VanderLugt correlator is demonstrated experimentally.

Correlation with spherical wave illumination

In the classical Van der Lugt correlator the plane wave illumination beam has been replaced by a spherical wave to avoid overshining of the undiffracted light in the photographic emulsion when weakly modulated objects have to be correlated. So the object information will be spread over a larger hologram area and an additional spatial frequency filter may be introduced without lengthening the experimental arrangement.

Increasing the holographic matched filter information capacity

The advantage of a sampled Fourier hologram in enhancement of the number of characters included in a matched spatial filter in Vander Lugt correlator systems is shown in this paper. A sampled Fourier hologram can be easily obtained by inserting a sampling mask adjacent to the hologram during recording. When the sampling period in the recorded sampled hologram is matched to the object spectrum, according to the Whittaker-Shannon theorem, the resulting image does not suffer any loss of information content. However, the sampled hologram covers only a small part of the photographic plate, with the result that one can record many closely packed Fourier holograms on the same area of the plate and at the same working point of the H-D curve. Thus, sampling is used as a multiplexing technique. Sets of cross-correlation or autocorrelation images are generated in the output of the correlator system. The offset angle of the reference beam must be suitably selected to prevent overlapping of the sets of images.