Fabrication of a binary-phase-only filter (BPOF) on transparency film

A novel method is employed to provide a quick and convenient means for converting a computer generated binary-phase-only filter (BPOF) into a representative optical element that can be tested in the laboratory. Intensity mapped BPOFs are generated using commercial transparency films and later the investigation extends to silver halide emulsions and photopolymers. Our results indicate that this can be a useful process with future applications for optical correlators and optical processors. The generated BPOFs can be made available not only for model verification, but also for direct fabrication of filter elements in an optical system — thus eliminating the need for more expensive alternatives.     

CRT－LCLV and photorefractive crystl BSO based real－time joint transform correlator

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Phase filters for correlators with incoherent light

Optimized phase filters can be designed and incorporated into hybrid electronic-optic correlators that exploit incoherent light. These filters lead to high optical efficiency and little, if any, loss of information that normally result from discarding amplitude data. The optimization procedure was experimentally tested by recording optimized filters in photo resist and incorporating them into the correlator. The optimization algorithm, the filter recording procedures, and the experiment correlation results demonstrating the efficacy of our design are presented. These results are superior when compared to those of correlators using holographic filters.     

Hoe/lensless matched spatial filter wavelength-scaling correlator

A scaling correlator optical pattern recognition system is described in which a lensless matched spatial filter (with the second Fourier transform lens and the matched spatial filter recorded on the same plate) is used with a first Fourier transform lens that is also an holographic optical element. The matched spatial filter is recorded at one wavelength and correlation is obtained at a second wavelength. Experimental demonstration and output correlation SNR data are reported, together with a comparison of the system's noise level using conventional optics and holographic elements.     

Efficiency improvement of optical pattern recognition in ultra-fast all-optical intensity equalizer

To cope with a larger intensity fluctuation of optical signals in optical communication networks, we have proposed and demonstrated an ultra-fast all-optical intensity equalizer based on an optical pattern recognition technique. To achieve higher transfer efficiency for this equalizer, we designed and fabricated a highly-efficient optical amplitude-phase filter using a diffractive optical element for optical pattern recognition. The fabricated amplitude-phase filter provides a diffraction efficiency of 85%, and the all-optical intensity equalizer is demonstrated to have higher transfer efficiency, when this filter is used.     

Accuracy and space bandwidth in space variant optical correlators

Numerous space variant optical pattern recognition systems using coordinate transformations have been reported recently. In this paper, we consider the required space bandwidth of these systems and the resultant accuracy of these novel deformation invariant correlators.     

Diffraction correlators invariant to the shift of optical elements

Linear in intensity image processing systems based on the principles of diffraction optics are considered in the paper. Influence of optical element shifts on calculation accuracy in the systems is studied. It is shown that image processing in the diffraction intensity correlators (vignetting, partial coherence, etc. are not taken into account) is absolutely invariant to longitudinal shifts of a holographic filter and, to a great extent, invariant to longitudinal shifts of objectives. The experiments show that the correlators operate rather stable with the optical elements shifted within 10% from the focal lengths of the objectives used, which is higher by two orders than the analogous limits in the diffraction amplitude correlators.     

Optical demonstration of shift-, rotation- and limited size-invariant pattern recognition using a circular harmonic-synthetic discrimination function filter

Optical means of performing pattern recognition possessing shift-, rotation- and limited size-invariance is demonstrated. The experimental set-up is a standard Fourier transform correlator with a binary circular harmonic (CGH) filter. The filtering function of the filter is obtained by the synthetic discriminant functions (SDF) method. In the process of synthesizing the filtering function, circular harmonic functions are chosen as the basic functions. Both optical results and computer simulation results demonstrate that the filter is able to recognize the target in every rotational orientation and in the relative size range of 1–1.82.     

Increase of reliability of surface displacement field recovery by optical speckle-displacement correlation technique

The optical speckle-displacement correlation (OSDC) technique was developed to increase the reliability of surface displacement field recovery near stress concentrators. The performance of optical speckle correlators based on joint transform correlator (JTC) architecture and a joint power spectrum (JPS) nonlinear filtering (median thresholding, adaptive median thresholding, ring median thresholding) is studied by using computer models of these correlators. The design of hybrid joint transform speckle correlator is detailed. Example results of correlation signal using computer models of digital speckle correlation and OSDC techniques and created hybrid joint transform speckle correlator setup are described.     

Optical Entropy Network Mapped from Binary Feature Tree

The concept of a binary feature tree (BFT) and the principle of its formation are described. A pattern is divided into sub-parts by comparing its similarity with other patterns. The BFT is established by sub-parts of a group of patterns and mapped into a three layered neural network which Sethi called an entropy network. The interconnection pattern between the first and hidden layers is formed according to the “AND“ relationship of node feature patterns determined by BFT. The interconnection pattern between the hidden and last layers is obtained by training. The advantage of the proposed network is that the scale is small because a feature neuron is adopted and the interconnection is local instead of full; therefore, it is easily implemented by either hardware or software. Two simulation examples show the success of the entropy network for pattern recognition. A feature extraction by an optical inner product method is also described.Presented at 1996 International Topical Meeting on Optical Computing (OC ‘96), April 21-25, Sendai, Japan.     

Tuneable edge enhancement filters for optical correlation

Difference of Gaussian (DOG) filters, a form of wavelet filter, are an extremely useful preprocessing tool for the enhancement of image edge data. The DOG filter is highly tuneable by control of the standard deviations of its constituent Gaussian distributions. These can be used in the frequency plane of optical correlators and implemented in the form of a static non-updateable filter. This article reports on a simple optical technique using photorefractive materials whereby a filter, updateable in real time and very similar to the DOG filter, is implemented by tuning the intensity of the hologram reference wave to give enhanced modulation in a selectable frequency band. This is called a tuneable photorefractive (TPR) filter. The results of the DOG and TPR filters are compared with those of the phase-only filter and classical matched spatial filter with respect to the criteria of signal-to-noise ratio, Horner efficiency and discrimination capability.     

光学小波包变换及其滤波器的研究

基于对光学小波变换必要条件的分析,提出光学小波包变换的概念.选出虹膜图库的联合最优小波包基,利用最优基的线性组合生成相应的复合光学小波包滤波器.将滤波器用于光电混合虹膜识别系统中对待识别输入进行小波包特征提取预处理,模拟结果不仅证明引入该滤波器可明显提升系统的识别效果,也证明了光学小波包变换提出的意义.     

Phase-only filtering based on sliced orthogonal nonlinear generalized decomposition

The sliced orthogonal nonlinear generalized (SONG) decomposition and correlation have been demonstrated to be powerful tools in digital image processing and promising for nonlinear optical information processing. In this paper, we propose an optical phase-only filtering system based on SONG decomposition (PBS), in which the phase-only filtering of the target and the input scene binary slices are performed separately by pairs and then added together. We numerically show that the PBS has extremely high and sharp output correlation peak compared with other optical correlators. Furthermore, such a SONG decomposition based phase-only filtering naturally inherits the nature of SONG decomposition, which has strong robustness to additive Gaussian noise and substitutive noise, and also the high light efficiency of phase-only filtering. We demonstrate that the PBS may serve as an optimized optical correlation scheme, which is promising in nonlinear optical pattern recognition.     

用相关矩阵特征判据法实现三重不变光学图像识别

本文首先在K-L变换中用相关矩阵作为特征判据进行特征压缩,然后用综合判别函数法制备空间综合匹配滤波器,可以有效地压缩特征图像数目.用这种滤波器实现了平移、旋转、尺度三重不变光学图像识别,且有较高的信噪比.     

基于混合类间联想神经网络的光学模式识别

通过结合自联合模型与异联想模型，提出了一种混合类间联想神经网络的光学模式识别系统。在该神经网络中，输入模式矢量不仅通过自联想识别自身，还通过异联想识别配对矢量，因而提高了识别概率。与匹配滤波器光学模式识别系统相比，识别结果直接，系统简单可行。     

Spectral band invariant wavelet-modified MACH filter

Filters synthesized with images of a specific spectral band in general fail to recognize targets in a different spectral band. In this paper, we therefore demonstrate the use of the wavelet-modified maximum average correlation height (WaveMACH) filter for automatic target recognition applications in both the visible and infrared (IR) spectral bands. As any input target appears different when imaged through two different sensors, i.e., a CCD or an IR camera, a WaveMACH filter synthesized using a CCD image shows no correlation with the image of the same target from an IR camera and vice-versa. Hence, separate filters are required to match the input targets from the two sensors. To avoid the synthesis and storage of separate filters, the images from CCD and IR camera are fused using Daubechies wavelet and then the rotation-invariant WaveMACH filter generated with the fused image. In all, 18 WaveMACH filters (each of 20° range) are required for in-plane rotation invariance in both the spectral bands for the full range of 0–360°. Computer simulation and experimental results implemented in hybrid digital–optical correlator architecture are shown for the proposed idea. The same filters have also been used to identify multiple targets in a scene. Performance measures like peak-to-sidelobe ratio (PSR), peak correlation energy (PCE) and correlation peak intensity (CPI) have been calculated as metrics of goodness.     

光学小波匹配滤波器与图形识别

小波变换弥补了傅里叶变换的不足，在信号及图像处理方面具有广阔的应用前景。文章深入讨论了小波变换匹配滤波器的理论基础及光学实现方法，并将其用于图形识别，给出了计算机模拟结果，与传统的匹配滤波器进行了比较，证实了小波变换在光学信息处理中的优越性。     

一种抗尺度畸变的光学相关图像识别技术

为提高光学相关图像识别的准确度和抗畸变能力,引入多重复合匹配滤波器概念,探讨一种新的识别思路。它融合了综合鉴别函数和K-L变换的经典思想,改善了单个匹配滤波器动态范围太小的状况,对图像尺度变换有较宽的适应范围,从而提高了光学模式识别系统的识别效率。仿真结果表明,对尺度缩小1/2的情况,采用此思路可使其滤波的刷新速度比常规方法提高4倍,从而验证了算法的有效性和可行性。     

Optimal Incoherent Filtering for Distortion-Invariant Image Recognition

An optimal incoherent filter is proposed for distortion-invariant correlation. The optical transfer function (OTF) of the correlator is specified as a realizable phase-only term which is optimized by the simulated annealing algorithm. The phase-only OTF is used in image recognition to produce a sharp peak response and can be generated by dual-filter synthesis. Image recognition is achieved by subtracting two spatially incoherent correlation outputs produced from a positive and negative filters with an input image. Computer simulations show that the proposed correlator can yield a sharp correlation peak with excellent distortion tolerance.Presented at 1996 International Topical Meeting on Optical Computing (OC ‘96), April 21–25, Sendai, Japan     

Analysis of Off-Axial Optical Systems (2)

The extended 4×4 Gaussian bracket matrix Gij represents the lowest order quantity of “aberration coefficient tensor quantities” which are defined to as the peculiarity of off-axial optical systems and are independent of azimuths. We newly confirmed this extended 4×4 Gaussian bracket matrix of deflection (refraction or reflection), transmission and “twisting.” The result determined by use of a new representative method of asymmetrical surfaces and a method of paraxial expansion along the folded reference axis shows that the 4×4 Gaussian bracket matrix is the extended form of the 2x2 Gaussian bracket matrix which is used in co-axial rotational symmetric optical systems. Furthermore, we analyze and formalize the crossterm effects, which are the most serious problem in optical systems having multiple off-axial surfaces, using the concept of a chain of “optical systems divided into former and latter” and the vector-tensor analysis method. The result of this analysis reveals the structure of the cross-term effects and proves the usefulness of the vector-tensor analysis method in general image analysis.