Comparison of vander lugt and joint transform correlators

Fourier filter augmented with trainer histograms

This paper describes a computationally efficient method for boosting the performance of correlation filters. The correlation filter is augmented with an array of histograms and the associated affinity numbers, obtained from the training image set utilized in construction of the filter. In the operational phase, histograms of sensor images are examined only at the image neighborhoods where the correlation filter provides initial indications of a target occurrence. The presence of a target is affirmed at image locations that pass both the peak cross correlation and histogram tests. Results of numerous experiments demonstrate that reinforcement of the spatial correlation filter with the trainer histograms leads to more robust Fourier filters for target detection and classification.

Optical correlation of spatial-frequency-shifted images in a photorefractive BSO correlator

The optical cross correlation of an image with another image that was spatial-frequency shifted in one dimension was demonstrated in a photorefractive VanderLugt correlator. The first image was stored as a Fourier-transform hologram in a photorefractive Bi12SiO20 crystal (BSO) and was successively correlated with different spatial-frequency-shifted versions of a second image. We implemented the spatial-frequency shift by rotating a galvanometer mirror in an image plane, causing the Fourier transform to be shifted laterally in the BSO. We verified that the resulting operation in the BSO was an accurate complex multiplication of the shifted and the stored Fourier transforms. As many as 20 successive readouts were conducted without measurable erasure of the stored hologram. The dynamic range, saturation behavior, and other performance parameters were measured and are discussed.

Reduction of the effect of aberrations in a joint-transform correlator

We report the study of the influence of optical aberrations in a joint-transform correlator: The wave aberration of the optical system is computed from data obtained by ray tracing. Three situations are explored: We consider the aberration only in the first diffraction stage (generation of power spectrum), then only in the second (transformation of the power spectrum into correlation), and finally in both stages simultaneously. The results show that the quality of the correlation is determined mostly by the aberrations of the first diffraction stage and that we can optimize the setup by moving the cameras along the optical axis to a suitable position. The good agreement between the predicted data and the experimental results shows that the method explains well the behavior of optical diffraction systems when aberrations are taken into account.

Color image recognition by use of a joint transform correlator of three liquid-crystal televisions

We present a joint transform correlator for color image recognition by using three liquid-crystal spatial light modulators. A method for simultaneously obtaining the correlation peaks of red, green, and blue is proposed and experimentally demonstrated.

Three-dimensional object recognition by fourier transform profilometry

An automatic method for three-dimensional (3-D) shape recognition is proposed. It combines the Fourier transform profilometry technique with a real-time recognition setup such as the joint transform correlator (JTC). A grating is projected onto the object surface resulting in a distorted grating pattern. Since this pattern carries information about the depth and the shape of the object, their comparison provides a method for recognizing 3-D objects in real time. A two-cycle JTC is used for this purpose. Experimental results demonstrate the theory and show the utility of the new proposed method.

Optical image correlator realized with a hybrid liquid-crystal-photoconducting polymer structure

A joint Fourier-transform optical correlator for image recognition based on a novel hybrid photoconducting polymer-nematic liquid-crystal structure is described. The optically addressed active element that we have designed is capable of performing real-time image processing 20 times/s, at light-intensity levels of 10mW/cm(2) with dc operating voltage of the order of 10 V. We present the results of correlation of simple objects as well as complicated photographs. The sensitivity, durability, and reliability of the presented system open possibilities for many applications.

Nonlinear morphological correlation: optoelectronic implementation

An optoelectronic implementation of the nonlinear morphological correlation by use of a threshold-decomposition technique and a joint transform correlator architecture is presented. This nonlinear morphological correlation provides improved image detection compared with standard linear optical pattern-recognition correlation methods. It also offers a more robust detection of low-intensity images in the presence of high-intensity patterns to be rejected.

Rotation-invariant joint transform correlator

We propose a new method for a rotation-invariant joint transform correlator that uses a rotating reference image that can potentially be applied to machine vision.

Biological photochrome bacteriorhodopsin and its genetic variant Asp96 ? Asn as media for optical pattern recognition

The biological photochrome bacteriorhodopsin (BR) is contained within the purple membrane (PM) of Halobacterium halobium. Artificial derivatives with improved optical properties can be generated by genetic methods and isolated from mutated halobacterial strains. The use of PM films that contain wild-type BR and BR variants as real-time recording media for various holographic applications has been reported previously, and the advantages of BR variants have been demonstrated. The high reversibility (>> 10(5) record/erase cycles), the fast time scale of its photoconversions (femtoseconds to milliseconds), and the large photochromic shift ( approximately 160 nm) occurring during its photocycle make it a promising material for real-time applications. A dual-axis joint-Fourier-transform (DA-JFT) correlator is used to demonstrate the applicability of PM films in holographic pattern recognition. One major advantage of PM films in this application is their high spatial resolution of more than 5000 lines/mm. Severe restrictions on the overall performance of the DA-JFT correlator system are caused by scattered light and result in a low signal-to-noise ratio. Since PM patches typically have a diameter in the range of the visible wavelengthsthat are used for hologram recording, light scattering is an intrinsic problem of PM films. The polarization recording properties of PM films are employed to overcome this problem. More than 20-fold improvement of the signal-to-noise ratio in the DA-JFT correlator output is obtained.

Bacteriorhodopsin: a biological material for information processing

Technology which makes use of biological materials has advanced dramatically in the last few decades. Production of specific biochemicals by selected microbial strains, the use of enzymes for stereospecific biosynthesis of materials and gene technological production of biologically important macromolecules are a few examples of these developments.