Sampling rate selection for a digital matched filter

The problem of selecting the sampling rate for the digital implementation of a matched filter for noncoherent digital communications is considered. The effects of bandwidth reduction and sampling are evaluated. A Nyquist rate of 8 samples per bit is found to be the critical value even with respect to the dependence on the carrier phase.     

Automatic optic disc detection from retinal images by a line operator

Under the framework of computer-aided eye disease diagnosis, this paper presents an automatic optic disc (OD) detection technique. The proposed technique makes use of the unique circular brightness structure associated with the OD, i.e., the OD usually has a circular shape and is brighter than the surrounding pixels whose intensity becomes darker gradually with their distances from the OD center. A line operator is designed to capture such circular brightness structure, which evaluates the image brightness variation along multiple line segments of specific orientations that pass through each retinal image pixel. The orientation of the line segment with the minimum/maximum variation has specific pattern that can be used to locate the OD accurately. The proposed technique has been tested over four public datasets that include 130, 89, 40, and 81 images of healthy and pathological retinas, respectively. Experiments show that the designed line operator is tolerant to different types of retinal lesion and imaging artifacts, and an average OD detection accuracy of 97.4% is obtained.     

Locating blood vessels in retinal images by piecewise threshold probing of a matched filter response

We describe an automated method to locate and outline blood vessels in images of the ocular fundus. Such a tool should prove useful to eye care specialists for purposes of patient screening, treatment evaluation, and clinical study. Our method differs from previously known methods in that it uses local and global vessel features cooperatively to segment the vessel network. We evaluate our method using hand-labeled ground truth segmentations of 20 images. A plot of the operating characteristic shows that our method reduces false positives by as much as 15 times over basic thresholding of a matched filter response (MFR), at up to a 75% true positive rate. For a baseline, we also compared the ground truth against a second hand-labeling, yielding a 90% true positive and a 4% false positive detection rate, on average. These numbers suggest there is still room for a 15% true positive rate improvement, with the same false positive rate, over our method. We are making all our images and hand labelings publicly available for interested researchers to use in evaluating related methods.     

Detection of optic disc in retinal images by means of a geometrical model of vessel structure

We present here a new method to identify the position of the optic disc (OD) in retinal fundus images. The method is based on the preliminary detection of the main retinal vessels. All retinal vessels originate from the OD and their path follows a similar directional pattern (parabolic course) in all images. To describe the general direction of retinal vessels at any given position in the image, a geometrical parametric model was proposed, where two of the model parameters are the coordinates of the OD center. Using as experimental data samples of vessel centerline points and corresponding vessel directions, provided by any vessel identification procedure, model parameters were identified by means of a simulated annealing optimization technique. These estimated values provide the coordinates of the center of OD. A Matlab prototype implementing this method was developed. An evaluation of the proposed procedure was performed using the set of 81 images from the STARE project, containing images from both normal and pathological subjects. The OD position was correctly identified in 79 out of 81 images (98%), even in rather difficult pathological situations.     

用TMSC54x开发系统实现FIR数字滤波器

简要介绍了单片数字信号处理器TMS320C54x的开发环境，叙述了用TMSC320C54x开发系统实现FIR滤波器的过程，给出了具体功能模块和程序流程。     

Automatic detection of red lesions in digital color fundus photographs

The robust detection of red lesions in digital color fundus photographs is a critical step in the development of automated screening systems for diabetic retinopathy. In this paper, a novel red lesion detection method is presented based on a hybrid approach, combining prior works by Spencer et al. (1996) and Frame et al. (1998) with two important new contributions. The first contribution is a new red lesion candidate detection system based on pixel classification. Using this technique, vasculature and red lesions are separated from the background of the image. After removal of the connected vasculature the remaining objects are considered possible red lesions. Second, an extensive number of new features are added to those proposed by Spencer-Frame. The detected candidate objects are classified using all features and a k-nearest neighbor classifier. An extensive evaluation was performed on a test set composed of images representative of those normally found in a screening set. When determining whether an image contains red lesions the system achieves a sensitivity of 100% at a specificity of 87%. The method is compared with several different automatic systems and is shown to outperform them all. Performance is close to that of a human expert examining the images for the presence of red lesions.     

层次优化目标与背景的匹配滤波高光谱目标探测研究

匹配滤波(MF)算法通过比较待探测像元到目标类和背景类中心的马氏距离来判断目标和背景,但是无法知道高光谱图像背景和目标的相关统计信息,只能做一些假设,导致探测结果不准确.本文在MF探测完成后,设定阈值进行分割,对背景和目标进行重新划分,获取背景和目标的相关统计信息.为了更好地获得两类的统计信息,我们利用迭代的方法逐层次...     

Detection and measurement of retinal vessels in fundus images using amplitude modified second-order Gaussian filter

In this paper, the fitness of estimating vessel profiles with Gaussian function is evaluated and an amplitude-modified second-order Gaussian filter is proposed for the detection and measurement of vessels. Mathematical analysis is given and supported by a simulation and experiments to demonstrate that the vessel width can be measured in linear relationship with the "spreading factor" of the matched filter when the magnitude coefficient of the filter is suitably assigned. The absolute value of vessel diameter can be determined simply by using a precalibrated line, which is typically required since images are always system dependent. The experiment shows that the inclusion of the width measurement in the detection process can improve the performance of matched filter and result in a significant increase in success rate of detection.     

Evaluation of the false alarm and detection probabilities in a spread spectrum system using a matched filter

A new method for the evaluation of the false alarm and detection probabilities in a direct sequence spread spectrum system using a matched filter for initial synchronization is presented. The probability of false alarms is evaluated by considering the number of consecutive secondary peaks, spaced by T_b (the bit duration), which exceed a predetermined value set at the threshold detector, in a time frame of a preassigned number of received bits. The probability of detection is similarly evaluated. Numerical results for a number of m-PN spreading sequences using low SNR values and various threshold values have been obtained. For a 127 length m-PN sequence, values of p_fa of the order of 1 × 10^?12 and of P_d of the order of 0-9 can be obtained at ?8dB SNR.     

Automatic detection of ship target and motion direction in visual images

In this article, we focus on automatic ship target detection in visual images. The proposed approach consists of two stages. At the first stage, emphasis is placed on sea background suppression. A pre-processing technique is studied based on mean-shift smoothing algorithm. In this process, the improvement is that we associate the range bandwidth of mean-shift with local image properties, thus achieve the purpose of suppressing sea background while protecting ship target. At the second stage, a hierarchical ship target detection approach is developed. To begin with, region-of-interest (ROI) of ship target is coarsely identified via salient edge regions extraction. Then main body of ship target is located by projection, prior spatial structure information of ship target is used for further ROI refinement. After that, a post-processing procedure based on colour features is presented to obtain final detection results. One advantage of the proposed method is that motion direction of the ship target can also be estimated, which could provide important information for ship target tracking and monitoring. Tested on real visual ship target images supplied by the co-operator, experimental results show that the proposed algorithm can effectively detect big ship targets and its motion direction with various backgrounds in visual images.     

A multimodal registration algorithm of eye fundus images usingvessels detection and Hough transform

Image registration is a real challenge because physicians handle many images. Temporal registration is necessary in order to follow the various steps of a disease, whereas multimodal registration allows us to improve the identification of some lesions or to compare pieces of information gathered from different sources. This paper presents an algorithm for temporal and/or multimodal registration of retinal images based on point correspondence. As an example, the algorithm has been applied to the registration of fluorescein images (obtained after a fluorescein dye injection) with green images (green filter of a color image). The vascular tree is first detected in each type of images and bifurcation points are labeled with surrounding vessel orientations. An angle-based invariant is then computed in order to give a probability for two points to match. Then a Bayesian Hough transform is used to sort the transformations with their respective likelihoods. A precise affine estimate is finally computed for most likely transformations. The best transformation is chosen for registration.     

Clustering to improve matched filter detection of weak gas plumesin hyperspectral thermal imagery

The use of matched filters on hyperspectral data has made it possible to detect faint signatures. This study uses a modified k-means clustering to improve matched filter performance. Several simple bivariate cases are examined in detail, and the interaction of filtering and partitioning is discussed. The authors show that clustering can reduce within-class variance and group pixels with similar correlation structures. Both of these features improve filter performance. The traditional k-means algorithm is modified to work with a sample of the image at each iteration and is tested against two hyperspectral datasets. A new “extreme” centroid initialization technique is introduced and shown to speed convergence. Several matched filtering formulations (the simple matched filter, the clutter matched filter, and the saturated matched filter) are compared for a variety of number of classes and synthetic hyperspectral images. The performance of the various clutter matched filter formulations is similar, all are about an order of magnitude better than the simple matched filter. Clustering is found to improve the performance of all matched filter formulations by a factor of two to five. Clustering in conjunction with clutter matched filtering can improve fifty-fold over the simple case, enabling very weak signals to be detected in hyperspectral images     

注意力残差链式融合的彩色眼底图像硬性渗出检测

硬性渗出物(Hard Exudate,HE)对糖尿病视网膜病 变(Diabetic Retinopathy,DR)的早期诊断具有重要意义,从彩色眼底图像中准确检测出HE 是诊断和筛查DR的重要步骤。针对以往自动检测方法中存在的分割效果不佳和对小目标误检 率高的问题,本文在经典U-Net生成网络的基础上,引入注意力残差链式融合机制,构造出 一种适用于视网膜HE检测的注意力残差链式融合生成对抗网络(Chain fusion of attention residuals GAN,CFAR-GAN)。该网络在生成网络编码过程的每个子模块后添加一个残差网 络(Residual Network,ResNet)结构,并采用带有残差连接的卷积层链(Residual convolut ional layer path,Res path)建立不同层间的跳跃连接,同时将全局最大池化注意力机制 用于刻画不同深度特征的权重,以防止训练过程的过拟合从而提高网络的泛化能力。将CFAR -GAN用e-ophtha EX数据库的训练集进行训练,在其测试集上,检测敏感性、PPV和F-sco re分别为92.5%、88.7%和90.6%;将训练好的网络在另一个独立的DIARETDB1数据库上进行测试,敏感性、特异性和 准确性分别为100%、98.5%和99.1%,表明本文所提出的方法具有 理想的泛化能力,这对于准确高效地检测眼底图 像中的HE,实现DR早期的自动诊断具有积极 意义。     

投影数字散斑的立体匹配

立体视觉作为被动光学三维传感中最重要的距离感知技术,具有广阔的应用前景。立体匹配是整个立体视觉的难点和重点所在。传统的立体匹配中,平坦、缺乏纹理细节的三维面形的误匹配率较高。采用一种辅助投影数字散斑的方法,利用归一化协方差区域相关算法,解决了这个问题,并得到了满意的浓密视差图。     

Analysis of EMG signals by means of the matched wavelet transform

The authors apply the wavelet transform to the analysis of EMG signals. Exploiting the fact that, under certain conditions, the signal can be considered as the sum of scaled and delayed versions of a single prototype, we have chosen the mother wavelet so as to match the known shape of the basic component. Moreover, the input signal has been Shannon interpolated in order to improve the low scale resolution. The results in terms of MUAP detection and resolution are very encouraging, even in the presence of high levels of noise     

State-space description of a multirate digital filter

The concept of multirate sampling in a digital filter is discussed, and a generalised method using the state-space technique of describing and analysing a 2nd-order multirate digitalfilter is presented.     

Synthesis of a periodically time-varying digital filter

The paper presents an approximate method of periodically linear time-varying (PLTV) digital filter (DF) synthesis through mean values of their coefficients in time. The recursive and nonrecursive PLTV DFs of the first, second and arbitrary orders are considered. It is shown that PLTV DFs have distinguishing features which give them advantages in some applications in comparison with linear time-invariant (LTI) DFs     

Determination of pulse-transfer function of a digital filter from prescribed partial requirements

An integral formula is given which enables the unique determination of the pulse-transfer function (p.t.f.) of a linear-time-invariant (l.t.i.) digital filter from its real or imaginary part defined on the unit circle in the z?1 plane.     

Restoration of signals degraded by impulse noise by means of a low-distortion non-linear filter

A simple low-distortion non-linear filter for the restoration of signals degraded by random impulsive noise is proposed. It performs considerably better than a median filter, lowering the reproducing error both in mean-square and maximum-error sense, although being comparable in computing time and in terms of storage.     

Performance of a spatio-temporal matched filter receiver forDS/SSMA communications

A spatio-temporal matched filter receiver for direct-sequence spread-spectrum multiple-access (DS/SSMA) communications with aperiodic random quadriphase spreading sequences is derived, and the system performance is analyzed. It is shown with the method of characteristic functions that the cross-correlation coefficients between the desired user's and the interfering users' spreading sequences tend, in distribution, to independently and identically distributed circularly symmetric complex Gaussian random variables as the processing gain goes to infinity. Based on this Gaussian approximation, the structure of the spatio-temporal matched filter receiver is derived and a bit error rate formula is obtained. Using Monte-Carlo simulations, as well as analytical methods, it is shown that the spatio-temporal matched filter receiver achieves a significant performance improvement over the conventional, temporal, and spatial matched filter receivers by effectively suppressing the multiple access interference