Nonlinear optical processing techniques that produce space- time information processing are introduced and experimentally demonstrated. The basic concept of such space-time processors closely resembles conventional Fourier optical processors of the space domain. By using ultrafast short pulses and nonlinear optics, we can perform not only real-time optical information conversion between the space and time domains, but also the processing and imaging of temporal information.
The scope of this work is the compensation of the chromatic dispersion inherent to free-space light propagation, both in the Fraunhofer and in the Fresnel diffraction region. The cornerstone of our procedure lies in achieving, in a first- order approximation, the incoherent superposition of the monochromatic versions of the selected diffraction pattern in a single plane and with the same scale for all the wavelengths of the incident light. Our novel optical configurations with achromatic properties for the field diffracted by a screen are formed by a proper combination of a small number of conventional diffractive and refractive lenses, providing an achromatic real image of the diffraction pattern of interest. The residual chromatic aberrations in every case are low even when the spectrum of the incident light spreads over the whole visible region. The resulting achromatic hybrid (diffractive- refractive) systems are applied, in a second stage, for implementing several achromatic diffraction-based applications with white light, like wavelength-independent spatial- frequency filtering, achromatic pattern recognition, white- light array generation, and to designing a totally-incoherent optical processor that is able to perform color processing operations under natural illumination (both spatially and temporally incoherent).
The paper describes the design concept of an optoelectronic system for real time image motion analysis. The system is proposed to be used onboard an Earth observation satellite for the real time recording of the image motion in the focal plane of the camera. With this record available, it is possible to use pushbroom scan cameras onboard satellites with moderate attitude stability (possible geometric distortions, caused by the attitude instability, can be corrected posteirori on base of the records). New experimental results are presented, which have been derived from a real-time breadboard model of the optical processor, developed and manufactured under ESA- contract. The results of the tests are provided as well as the expected performances of a full scale system.
An all new type of absolute, optical encoder with ultra-high sensitivity has been developed at NASA's Goddard Space Flight Center. These position measuring encoders are unconventional in that they rely on computational pattern recognition of high speed, electronic images, made of a moving, backlit scale which carries absolute position information of either linear or rotary format. The pattern recognition algorithms combine edge detection, threshold level sensing, spatial compression, and centroiding along with fault recovery through scale image defect detection. Details of the encoder scale patterns and their design rules and the image processing algorithm which gives these encoders their unique and unparalleled performance characteristics are discussed.
A previously proposed Hilbert transformoptical correlator modified th einut nd filtr images by adding an x-y mirror image t provide a real Fourie tnform. In an improved corrlator we cimpute the intnsity o the fourier trnsform so that filters are guarant4ed psoitiv end ral.The cente peak of the ouptu intnsity is shown to approximate the autoconvolutionof the convolution between the originalimags.The applcain of a Hilbert tranformallows only half of th eforuier plane to be used.This cn be used to speed the correltor by two or to perit an incrase in space-bandwidth product ofinput imgs by two. Result sof cmpute simulatin are shown.
We describe the principles and performance of a novel form of hybrid electronic/photonic correlator which exploits recent developments in both electronics and photonics to provide a fast, compact and rugged processor. In the earlier Vander Lugt correlator the input image is Fourier Transformed optically and multiplied optically with the conjugate Fourier Transform of a reference pattern; the required correlation function is completed by taking the inverse Fourier Transform of the product optically. The correlator described here is similar, but performs the initial Fourier Transforms and multiplication electronically. In this scheme the Fourier Transforms of both the input scene and reference pattern are reduced to a binary phase-only format, when the multiplication process simplifies to a simple Boolean logic XOR function. The output of this XOR gate is displayed on a state-of-the-art Fast Bit Plane Spatial Light Modulator (FBPSLM). This device is electrically addressed, and employs a ferroelectric liquid crystal so its operation is inherently binary and fast. A consequence of the use of binary phase-only data is the appearance of a second (unwanted) peak in the output plane, but we demonstrate its elimination through the introduction of a chirp function. The complete correlator is demonstrated operating at 10,500 correlations/sec.
We propose a method to extract features optically from the input pattern by use of an array of the Hough transform filters. Here the subparts of the input pattern are Hough transformed by their corresponding elements of the filter array independently and simultaneously. Being compared with the conventional method, in which the whole input pattern is Hough transformed by a single optical filter, our method provides not only the improved transform accuracy but also the approximate position information of the line segment features. To show the feasibility of our approach, we fabricated a 5 X 5 filter array and performed preliminary experiments.
The detection of image changes irrespective on geometric transformations are required in many applications. In this paper we present a novel use of the scale transform oriented to image identification and registration. If we translate a signal then all the information appears in the phase of the Fourier transform of the translated signal. Similarly, if we scale or rotate an image all the information about the amount of scaling or rotation appear in the phase of the scale transform. In the present study we report a very precise image identification technique based on the use of the power cepstrum of the scale transform. Cepstral filtering can be considered as a non-linear adaptive prefilter followed by an autocorrelation operation. The accuracy of the cepstrum techniques and the speed of the Fourier transform makes the present method faster and more robust to noise than other existing techniques. Image registration has been accomplished by computing the power cepstrum of the log-polar scale mapping. The performance of the improved method has been experimentally verified in a class of typed characters and diatom images in lighting microscopy.
Current trends in optical defect detection and surface analysis using spatial light modulators are discussed. Examples for microscopic as well as macroscopic measurements in two and three dimensions are shown. Results for adaptive fringe projection in combination with moire, for adaptive illumination for two-dimensional image processing, and for the detection of defects in periodic media will be presented. We also report on improved correlation methods for position detection.
Generation and processing of optical patterns in the optical feedback system composed of an optically addressable spatial light modulator and a two-dimensional optical feedback including a spatial frequency filter are demonstrated. The fringe pattern, which is generated by using a single slit, is used in order to estimate the spatial property of the system. An image made of circular isolated spots generated using a low-cut spatial frequency filter could be formed and memorized at the desired position by an external control light under both in-focusing condition and out-of-focusing condition of the optical feedback. Self-scanning isolated spots resulted from unisotropic transverse interactions memorize a spatiotemporal binary image and provide a delay line for them. Furthermore we demonstrate that the optical feedback system controlled by the spatial frequency filter generated in the optoelectronic feedback system performs a dynamic pattern generation.
An enhanced region-growing approach for segmenting regions is introduced. A region-growing algorithm is merged with stopping criteria based on a robust noise-tolerant edge-detection routine. The region-grow algorithm is then used to segment the shadow region in a Synthetic Aperture Radar (SAR) image. This approach recognizes that SAR phenomenology causes speckle in imagery even to the shadow area due to energy injected from the surrounding clutter and target. The speckled image makes determination of edges a difficult task even for the human observer. This paper outlines the edge-enhanced region grow approach and compares the results to three other segmentation approaches including the region-grow only approach, an automated-threshold approach based on a priori knowledge of the SAR target information, and the manual segmentation approach. The comparison is shown using a tri-metric inter- algorithmic approach. The metrics used to evaluate the segmentation include percent-pixels same (PPS), the partial- directed hausdorff (PDH) metric, and a shape-based metric based on the complex inner product (CIP). Experimental results indicate that the enhanced region-growing technique is a reasonable segmentation for the SAR target image chips obtained from the Moving and Stationary Target Acquisition and Recognition (MSTAR) program.
It is shown that the problem of classification of images that have the perfectly random nature may be solved with the help of synthetic discriminant functions being synthesized by least-squares technique to separate linearly the power spectra of the corresponding random image fields. The realization of the proposed method by means of an optical technique is discussed, and its efficiency is illustrated by two examples of real-life texture classification.
Autoradiography is a useful imaging technique to understand biological functions using tracers including radio isotopes (RI's). However, it is not easy to describe the distribution of different kinds of tracers simultaneously by conventional autoradiography using X-ray film or Imaging plate. Each tracer describes each corresponding biological function. Therefore, if we can simultaneously estimate distribution of different kinds of tracer materials, the multispectral autoradiography must be a quite powerful tool to better understand physiological mechanisms of organs. So we are developing a system using a solid state detector (SSD) with high energy- resolution. Here, we introduce an imaging technique with a coded aperture to get spatial and spectral information more efficiently. In this paper, the imaging principle is described, and its validity and fundamental property are discussed by both simulation and phantom experiments with RI's such as 201Tl, 99mTc, 67Ga, and 123I.
In this paper, we analyze decision boundaries of radial basis function (RBF) neural networks when the RBF neural networks are used as a classifier. We divide the working mechanism of the neural network into two parts: dimension expansion by hidden neurons and linear decision boundary formation by output neurons. First, we investigate the dimension expansion from the input space to the hidden neuron space and then address several properties of decision boundaries in the hidden neuron space that is defined by the outputs of the hidden neurons. Finally, we present a thorough analysis how the number of hidden neurons influences decision boundaries in the input space with illustrations, providing a helpful insight into how RBF networks define complex decision boundaries.
Generally fuzzy c-means algorithm is one proved that very well suited for remote sensing image segmentation, exhibited sensitivity to the initial guess with regard to both speed and stability. But it also showed sensitivity to noise. This paper proposes a fully automatic technique to obtain image clusters. A modified fuzzy c-means classification algorithm is used to provide a fuzzy partition. This method is less sensitive to noise as it filters the image while clustering it, which is based on the consideration of the neighbors as factors the attract pixels into their cluster. The experimental results on JERS-1/SAR image demonstrate its potential usefulness.
We present a fast algorithm for the off-plane near-field computer generated hologram (CGH). In this paper, we develop a fast and efficient algorithm to compute CGH data having higher resolution than optical hologram, by reducing redundant computation load. We use a moving window technique to eliminate the high spatial frequency component and to speed it up. To implement a real-time interactive CGH, one has to speed it up and reduce the computation load. So, we use pre-computed look-up table technique which contains large arrays of interference fringe patterns of possible distance point sources. To speed up further, we use the bipolar intensity and a relaxed CGH which has less resolution in vertical component than it does that in horizon one. In experiment, the computed CGH data are displayed on a liquid-crystal television spatial light modulator. We show that a 3-dimension image is reconstructed well by illuminating the laser on the hologram plate.
A double random phase optical encryption system that uses a binary key code is proposed. The key code is generated as a binary computer generated hologram. The binary key code can be displayed on a binary spatial light modulator such as a ferroelectric liquid crystal display. The use of a binary spatial light modulator enables us to renew the key at high speed. A joint transform correlator based on a photorefractive crystal in the Fourier domain is used to perform shift invariant encryption and decryption. Computer simulations of the effects of using a binary encoded key code instead of a complex amplitude key code are shown. Preliminary optical experimental results are presented to demonstrate the effectiveness of the proposed system.
A method is presented to store biometric and/or other important information on an ID card in the form of a Card Hologram that cannot be read or duplicated without the use of a special Key Hologram that is secured inside of an automated reader. The Key Hologram produces the unique wavefront required to release the information contained in a complex, 3- D diffraction pattern recorded in a volume hologram attached to the card. Experimental results are presented in which the image of an Air Force resolution target are recorded and reconstructed in a volume material using a random speckle wavefront and that cannot be viewed using a simple wavefront such as a collimated or diverging laser beam.
The dual nonlinear correlation processor is proposed to recognize occluded images. The analysis of the digital results of recognition is presented. The influence of the variable discrimination capability of the processor for the quality of correlation signal in the case of various level of occlusion and various information content of the apertured input scenes is shown.
We investigate the tolerance to data loss of a double random phase encoding encryption system. The signal-to-noise ratio of the decrypted image is investigated when a part of the encrypted image is lost. The SNR can be enhanced by reducing the ratio of the sampling number of the image to the total sampling number when electronic implementation is performed. In optical implementation, the SNR can be increased by using a phase mask with higher spatial frequency. Both the theory and computer simulations are demonstrated.
The problem of detection by optical correlation of an apertured input scenes has been analyzed by digital simulation and in an optical experiment. The chosen input scenes included various kinds of elements with different Fourier spectrum: high, medium, or low frequency. Digital and optical recognition results (correlation peak value, PCE ratio, and peak location) are discussed as a function of various level of occlusion and various information content of the input scenes.
The possibilities of using of optical and hybrid joint transform correlator (JTC) architectures for construction of security devices with usage of the transformed phase masks (PMs) as optical marks are investigated. With this purpose the yardsticks of an estimation of their efficiency, namely peak- to-noise ratio (PNR) and relative intensity of correlation peaks, are selected general for two types of JTCs. The idealized model of an interference noise in a linear JTC is designed, if the binary random PMs on input are entered. The relations of a PNR to dimension both PM and window ambient correlation peak are parsed. The optically addressed spatial light modulator (OASLM) based on the chalcogenide glass photoconductor -- nematic liquid crystal structure is studied. The experimental setup of an OASLM JTC is designed on the basis of this SLM. The relations a PNR and relative intensity versus an effective focal length are studied and the major factors limiting efficiency of the setup are parsed. The optoelectronic device based on a hybrid optical-digital JTC architecture is built. The relations to different conditions of a joint power spectrum recording by a CCD-camera in this device are investigated. The comparative analysis of two types of JTC is carried out also concluding about expediency of their usage for different security applications is made.
In this paper, we consider a simple object-independent diffuser for digital holography that is characterized by a constant absolute value of the phase difference between its samples. In order to have desirable characteristics, the distribution of the signs of phase difference of it must be sufficiently randomized. We thus propose an effective algorithm for this purpose. Finally, we show that this diffuser can be used to initialize the phase of an intensity object for successfully calculating its complex amplitude, which is band-limited and at the same time possesses a smooth spectrum, and which fulfills the basic requirement for efficiently encoding it into a hologram and reconstructing it with reduced speckles.
With the exceptional development and popularization of laser holography, the application of the holographic anti- counterfeiting identifiers is enlarging gradually. How to improve the quality of holograms for laser holography industries becomes very important. In recent years computer- generated holograms have been investigated intensively because of their wide application range and their advantages in term of flexibility, accuracy, light weight and cost. A method based on Iterated Function System for digital hologram synthesis is proposed in this paper. The method can generate the view angle combining digital holograms by resolving the affine transforms of IFS into many affine transforms of sub- images. The reconstructed sequence of images with multi- channel can be viewed in different angles and look like a kinetic-object. Thus our method provides a new way to laser holography anti-counterfeiting. The generated fractal kinetic holograms have been used in many security holograms.
We have applied the interference fringe scanning algorithms that are used in interference fringe analysis to an optical encoder as angle detection algorithms, in order to disperse the influence of sinusoid wave distortion from the encoder's photo detector. We also evaluated these algorithms with the analytical system and techniques for obtaining the same output signal as that of the actual encoder, by using image data on light intensity as the light permeates the slit disk of the encoder. As a result, we obtained about twice the angle precision by applying the algorithms to the optical encoder.
The front-of-screen quality as the visual performance of thin- film transistor liquid crystal displays were investigated using the original algorithm for uniformity analysis. Extraction and evaluation of 'mura,' which was low-contrast and non-uniform brightness region, was successfully demonstrated using commercial-available test system with our algorithm. The algorithm was led out from researching of sensory analysis and human perception. The sensitivity of the technique was demonstrated by a detectable change at even the small level which was perceptible by experienced manufacturing inspectors. The evaluation and judgement for 'mura' using our technique closely matched the results from the experienced inspectors.
In this paper, we analyze decision boundaries of 3 layer feedforward neural networks that use the sigmoid function as an activation function. By analyzing the decision boundaries in the space defined by the outputs of the hidden neurons, we found that the decision boundaries are always linear boundaries and that the decision boundaries are not completely independent. We found that for a 3-pattern class problem, the decision boundaries in the space defined by the outputs of the hidden neurons should meet at the same intersection. And this dependency of decision boundaries is extended to multiclass problems, providing valuable insight into decision boundaries. In particular, for a K-pattern classes problems, we found that there are only K-1 degree of freedoms in drawing decision boundaries in the space defined by the outputs of the hidden neurons, though there are KC2 decision boundaries. Finally, we present some interesting examples of decision boundaries of neural networks.
The performance of nonlinear joint transform correlators (JTCs) are experimentally tested with respect to in-plane and out-of-plane rotation distortions. Optical experiments are presented for both linear and nonlinear joint transform correlators. The robustness of these systems to rotation distortions is investigated. The results show that nonlinear JTCs perform similarly to linear JTCs in the presence of out- of-plane rotation distortions, but that nonlinear JTCs are more sensitive than linear JTCs to in-plane rotation distortions. However, it is well known that nonlinear JTCs have the desirable properties of illumination tolerance and discrimination sensitivity. To reduce the sensitivity of nonlinear JTCs to in-plane rotation distortions, the nonlinear joint power spectrum is multiplied by a circularly symmetric Gaussian function. This is equivalent to applying a Gaussian filter to the nonlinear JTC output. The experimental results show that using such a Gaussian filter provides nonlinear JTCs with similar in-plane rotation tolerance to that of linear JTCs.