Pattern recognition in hyperspectral imagery using one-dimensional shifted phase-encoded joint transform correlation

Pattern recognition in hyperspectral imagery is a challenging issue because of the high false alarm rate and computation complexity. In this paper, a one-dimensional shifted phase-encoded fringe-adjusted joint transform correlation (SPFJTC) technique is developed for hyperspectral image processing system. The proposed technique processes the reference spectral signature using a random phase mask and correlates it with the spectral signature corresponding to each pixel of the unknown input hyperspectral image cube using a simple architecture. This technique generates very high discrimination between the object of interest and background clutter. Computer simulation results using real life hyperspectral imagery show that the proposed SPFJTC technique can effectively recognize the objects of interest while alleviating the effects of false alarms and other artifacts.     

Rotation-invariant pattern recognition using morphological fringe-adjusted joint transform correlation

We propose a rotation-invariant nonlinear correlator based on circular harmonic filter (CHF) and morphological Fringe-adjusted Joint Transform correlation (MFJTC). We refer to this correlator as a rotation-invariant MFJTC (RIMFJTC). Through computer simulation, we compare the output results of RIMFJTC with those of rotation-invariant MC (RIMC) and CHF when input scene is corrupted by salt-and-pepper noise, white additive Gaussian noise and cluttered background. Our results show that RIMFJTC yields higher discriminability, sharper and higher correlation peaks, and displays better stability against the above three kinds of noise than do the RIMC and common CHF.     

Shift- and scale-invariant pattern recognition using morphological fringe-adjusted joint transform correlation

A shift- and scale-invariant version of morphological fringe-adjusted joint transform correlation (MFJTC) is proposed in this paper, which we call shift- and scale-invariant MFJTC (SIMFJTC). SIMFJTC is combination of MFJTC and conventional radial harmonic filter (RHF). Using computer simulation, we compare the output results of SIMFJTC with those of morphological radial harmonic correlation (MRHC) and SDF-based FPFJTC when input scene is corrupted by salt-and-pepper noise and cluttered background. Our results show that SIMFJTC has higher discriminability and displays better stability against salt-and-pepper noise and cluttered background. Moreover, scale-invariance of SIMFJTC is much stricter than MRHC and SDF-based FPFJTC.     

旋转不变二值化联合变换相关识别方法

介绍一种基于二值化联合变换相关的综合鉴别函数算法，用等相关峰及Gram-schmidt展开获得的综合鉴别函数对迭代算法进一步优化，获得了适用于二值化联合变换相关的综合鉴别函数。采用这种算法制作的综合鉴别滤波器既有相关峰值高和相关峰尖锐等特点,又能识别旋转图像。计算机模拟结果表明：这种相关器在信噪比、光能效率、相关峰尖锐度和鉴别能力上都有一定程度地提高，实现了较高鉴别率旋转不变光学模式识别。     

多目标识别的联合变换相关器的研究

提出了一种可用于多目标识别的联合变换相关器。为改善相关信号的性能,对功率谱作了优化处理。为消除相关面上的零级项和目标间的相关项,可用联合功率谱减去纯目标输入的功率谱和参考图像的功率谱;为增强和锐化相关峰,将相减的功率谱作指数函数滤波处理。分析了指数滤波参数对相关结果的影响。计算机模拟结果表明,这种相关器所输出的相关信号比经典联合变换相关器和二元联合变换相关器输出的相关信号更好,互相关得到了抑制,自相关得到了增强,具有很好的抗噪能力。     

Optical security system employing shifted phase-encoded joint transform correlation

A new optical security system is proposed using a shifted phase-encoded joint transform correlation (JTC) architecture. In the proposed technique, at first, the address code is fed into two channels where one channel is shifted by 180°. The output signals from both the channels are phase-masked and then added with the input image to be encrypted. The joint power spectrum (JPS) obtained from one channel is subtracted from the JPS of the other channel, and the modified JPS is inverse Fourier transformed to yield the encrypted image. For decryption, the received signal is Fourier transformed and multiplied by the phase mask and the address code, which is then inverse Fourier transformed to generate the output signal. The proposed technique does not require complex conjugate of the address code otherwise required in the classical double random phase encryption. Also the decryption result is much more enhanced when compared to the output generated by alternate JTC techniques. Computer simulation results verify that the encryption and decryption are very much secure and efficient in both noise-free and noisy conditions.     

基于联合变换相关的目标跟踪方法

成像跟踪制导中,相关跟踪技术占有重要的地位。基于联合变换相关的目标跟踪方法,使用图像序列的相邻两帧图像依次进行相关运算,提取相关结果中互相关峰的位置和相邻两帧图像时间间隔等信息,即可得到目标位置、方向和速度的变化情况。计算机仿真实验结果表明:该算法有效地解决了传统相关跟踪算法中存在累积误差和容易使目标漂移出其参考模板的问题,可以实现稳定跟踪。     

Binary phase only filters for rotation and scale invariant pattern recognition with the joint transform correlator

The joint transform correlator (JTC) is one of the two main optical image processing architecture which provides a highly effective way of comparing images in a wide range of applications. Traditionally, an optical correlator is used to compare an unknown input scene with a pre-captured reference image library, to detect if the reference occurs within the input. Strength of the correlation signal decreases rapidly as the input object rotates or varies in scale relative to the reference object. The aim of this paper is to overcome the intolerance of the JTC to rotation and scale changes in the target image. Many JTC systems are constructed with the use of ferroelectric liquid crystal (FLC) spatial light modulators (SLMs) as they provide fast two-dimensional binary modulation of coherent light. Due to the binary nature of the FLC SLMs used in the JTC systems, any image addressed to the device need to have some form of thresholding. Carefully thresholding the grey scale input plane and the joint power spectrum (JPS) has significant effect on the quality of correlation peaks and zero order (DC) noise. A new thresholding technique to binarise the JPS has been developed and implemented optically. This algorithm selectively enhances the desirable fringes in the JPS which provide correlation peaks of higher intensity. Zero order noise is further reduced when compared to existing thresholding techniques.Keeping in mind the architecture of the JTC and limitations of FLC SLMs, a new technique to design rotation and scale invariant binary phase only filters for the JTC architecture is presented. Filers design with this technique have limited dynamic range, higher discriminability among target and non-target objects, and convenience for implementation on FLC SLMs. Simulation and experiments shows excellent results of various rotation and scale invariant filters designed with this technique. A rotation invariant filter is needed for various machine vision applications of the JTC. By fixing the distance between camera and input object, the scale sensitivity of the correlator can be avoided. In contrast to the industrial machine vision applications, scale factor is very important factor for the applications of the JTC systems in defence and security. A security system using a scale invariant JTC will be able to detect a target object well in advance and will provide more time to take a decision.     

Performance of joint transform correlation under varying illumination and noise

The effect of varying the input scene illumination and noise on the performance of binary and fringe-adjusted joint transform correlators (JTCs) has been investigated in this paper. Simulation results show that the fringe-adjusted JTC yields superior correlation output when compared with the binary JTC for all types of input scenes affected by both illumination and noise. Furthermore, the binary JTC has been found to yield a good correlation output when zero mean, unity variance Gaussian white noise is added to input scenes affected by poor illumination.     

Improved approach for target detection and recognition on optoelectronic hybrid joint transform correlator

A conventional joint transform correlator (JTC) often generates large correlation sidelobes as well as a large correlation peak width, strong zero-order peak, and low diffraction efficiency in target detection and recognition, which make the detection ability of JTC lower. To conquer these difficulties, firstly, a joint power spectrum (JPS) subtraction technique was proposed in Fourier plane, where power spectrum of reference image and power spectrum of object image are subtracted from the JPS before inverse Fourier-transform operation, it is evident that the improved JPS removes the zero-order term. Secondly, a fringe-adjusted filter (FAF) was presented to restrain sidelobes and noises. The revised JPS is multiplied by a FAF before the inverse Fourier-transform operation to obtain the cross-correlation peak. Computer simulations showed the improved method can markedly eliminate zero-order diffraction and effectively control the sidelobes and noises compared to traditional JTC, and then enhance the detection ability for JTC. Experimental results presented the sharp correlation peak and also demonstrated this approach effectiveness.     

基于功率谱相减实现无零级衍射的联合变换相关器

联合变换相关器的零级衍射光斑会影响相关峰探测。将参考目标和待识别目标的联合功率谱与参考目标本身的功率谱做相减运算可消除零级衍射光斑,可提高联合变换相关器的识别能力。通过计算机仿真和实验验证了该方法的可行性。     

Optical classification of random image fields using spectral synthetic discriminant functions

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.     

Implementation of an algorithm for detecting patterns in defocused scenes using binary joint transform correlation

An original method to detect images in defocused scenes by means of a binary joint transform correlation is presented. Defocused images are described in frequency domain as the product between the Fourier transform of the in-focus scene by the optical transfer function of the imaging lens. This function, which presents positive and negative values, introduces sign errors in the joint power spectrum. The goal of this study is to detect the sign of the optical transfer function starting from the defocused image by means of a digital algorithm. Information provided by the algorithm allows to compensate the sign errors in the binary joint power spectrum and to obtain invariant correlations with respect to defocusing. Theoretical analysis and digital experiments to test the procedure are provided.     

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。