时空图像测速法的敏感性分析及不确定度评估

时空图像测速方法(STIV)是一种以测速线为分析区域、通过检测合成时空图像的纹理主方向估计一维时均流速测量方法。由于具有空间分辨率高、实时性强的优点,在河流水面流速、流量的实时监测中具有特别的应用潜力。但鉴于现场环境的复杂性和河道水流的变化性,现有研究在敏感性分析及不确定度评估方面尚存在不足,使得方法的实用性受限。对此设计了一种滚动画幅装置来模拟河流水面运动,并在此基础上全面开展了频域STIV方法的定量评估。相比数值模拟和现场比测的方法,该装置能够提供相对真实的测量环境和稳定的运动参数。实验结果表明:测速线长度和示踪条件是影响测量精度的主要敏感因素。通过合理的参数设置可以将方法的不确定度控制在±1%以内,能够满足水文测验的精度要求。     

基于时空图像频谱的时均流场重建方法

尽管大尺度粒子图像测速技术(LSPIV)在水流测速方面具有优势,但该方法得到的瞬时流场矢量正确率低,导致了时均流场重建误差大。提出了一种基于时空图像频谱的时均流场重建方法。首先利用示踪物在三维时空域中分布的相关性,通过在图像序列中设置的测速线合成时空图像;然后基于傅里叶变换的自配准性质建立时空图像纹理主方向和频谱主方向间的约束关系;最后采用由粗到精的搜索策略检测频谱主方向并估计测速线上一维运动矢量的大小。实验表明:采用此方法检测纹理图像频谱主方向可以达到0.1°的检测精度,对现场成像暗噪声类的干扰模式具有抗噪性,有效提高了时均流场重建的精确性。     

基于频域滤波的电缆线芯图像纹理消除研究

电缆作为电力传输的重要部分,其线芯质量关系到用电安全及传输效率。 在利用机器视觉技术测量电缆线芯结构参数 时,刀痕纹理严重影响了图像分割效果,降低了测量精度。 针对这一问题,提出了一种基于改进频域滤波的线芯截面图像刀痕 纹理消除方法:首先采用相对总变差模型分解线芯截面图像,得到纹理图像描述;对线芯截面纹理图像进行快速傅里叶变换,分 析刀痕纹理在频域中的能量主方向;研究改进型巴特沃斯陷波滤波器,设计椭圆形的邻域窄阻带以降低刀痕纹理对应的带状区 域能量,从而消除刀痕纹理。 实验结果表明,该方法的刀痕纹理消除率可达 92% ,提升了电缆线芯质量检测的效率。     

基于方向Gabor特征的水面尾迹提取

为了自动提取航空图像中水下目标运动产生的尾迹,提出一种基于方向Gabor特征和主成分分析(PCA)的水面尾迹自动提取算法.该算法首先对图像进行傅里叶变换得到它的能量谱,通过对传统的主成分分析进行改进求得图像的方向,然后根据方向来确定Gabor滤波器组,用该滤波器组提取的纹理特征就有旋转不变性.为了消除纹理特征的冗余信息,用主成分分析法对其进行降维,并对它们的分类性能进行比较.大量的实验结果表明本文的方法能够有效地提取水面尾迹纹理.     

近红外成像的便携式大尺度粒子图像测速仪

开发了一种用于河流表面流速场测量的便携式大尺度粒子图像测速仪(large-scale particle image velocimeter,LSPIV).该仪器基于一台以图像处理专用DSP为核心的智能相机,代替PC高效地完成图像采集和处理的任务.首先利用近红外波段下水流示踪物(弱小目标)和水体光强反射率的差异,在单色CMOS传感器前加装红外滤镜抑制水面光学噪声,增强弱小目标与背景间的对比度,提高了后续运动矢量估计中相关曲面的峰值信噪比.其次,提出了一种基于时空联合滤波的时均流场重建方法,利用河流流场中的先验和冗余信息识别并修正错误矢量,改善了天然河流中由于示踪物密度过低或分布不均造成的表面流速估值过低问题.最后,通过静水和动水条件下的2组现场实测验证了近红外成像系统及图像处理算法的有效性.     

河流水面成像测速研究进展

大尺度粒子图像测速(LSPIV)是一种用于测量大面积(数百平方米)水体表面流速的非接触式全场流速测量技术。不仅可用于常规条件下明渠紊动特性和时均特性的研究,更具有极端条件下河道水流监测的应用潜力。然而受复杂现场环境的影响,该技术在天然河流的应用中面临着诸多挑战。从水流示踪方式、流场图像采集、水面目标增强、运动矢量估计、时均流场重建、水面流场定标及不确定度评估七个方面综述了国内外对河流水面成像测速(RSIV)方法的研究进展。通过对现有方法的总结和讨论,提出改进技术方法的研究需求,以使其成为水动力学和水文学中有力的测量工具。     

一种基于多通道Gabor滤波的纹理提取方法

研究了一种在多种纹理叠加的复杂轮胎X光图像中进行纹理提取的新方法.轮胎X光纹理在频谱中被看作是局部空间频率的辐射模型,并且不同纹理对应的主频率聚集区域基本能相互分开.基于Gabor滤波器对空间频率的带通滤波能力以及方向、形状、带宽和通带中心频率的可调节特性,构造了多通道Gabor滤波器组提取每种纹理对应的主要频率成分,提取的频率成分经过频-时域变换就实现了纹理提取.考虑到实际纹理灰度分布不是理想的正弦分布,改进了传统的Gabor滤波方式,使其保留了纹理的低频成分.实验结果表明,图像中叠加的多种纹理能被准确提取,纹理区域边界也没有失真,并且有效降低了纹理之间频谱混迭造成的影响.     

基于Gabor滤波器的航空图像水面纹理自动提取

本文提出了一种基于Gabor滤波器的水面尾迹纹理的自动提取算法.该方法分为两步第一步,选取等大小的含尾迹纹理的水面子图像和不含尾迹纹理的水面子图像,通过一组GaBOR滤波器得到它们的特征图像,计算每个子图像特征图的均值和方差,将它们作为神经网络的训练样本对BP网络进行训练得到用于识别的网络;第二步,将待提取的整幅图像分成很多与第一步中子图像等大小的子图像,分别计算它们的Gabor特征图像,并得到它们的均值和方差,把它们作为神经网络的输入,得到它们是否是纹理区域,由整幅子图像的识别结果得到一幅二值图像,用Hough变换检测图像中的直线,根据直线的长度是否有尾迹存在.大量的实验结果表明该方法能够准确地提取尾迹纹理.     

基于HVS的自然场景图像特征提取方法

提出了基于人类视觉系统的自然场景图像颜色和纹理特征提取方法.介绍了两类低层图像特征颜色和纹理特征提取方法,分别提出了以自适应主导色原理来表示颜色特征、采用纹理灰度图的空频域特性表示空间纹理特征;以ACA方法获得自适应主导色、以可控金字塔滤波分解的方法获取纹理特征.同时还介绍了优化颜色构成距离度量和纹理距离度量,最后给出了实验结果和分析.     

基于仿生视觉的图像RST不变属性特征提取方法

针对图像目标识别过程中易受旋转、缩放、平移及噪声影响的问题,提出一种仿生物视觉感知的RST不变属性特征提取方法,以提升形变目标的识别率与抗噪鲁棒性。受生物视觉感知机理启发,其皮质细胞经过多级变换后,能够最佳权衡图像选择性与不变性。为此,该方法设计成两个阶段。第1阶段中,受生物视觉在水平与垂直方向响应强烈的启发,提出Gabor滤波器与双极滤波器融合的filter-to-filter方向边缘检测方法。Gabor滤波作为底层滤波器平滑图像,通过高层水平与垂直方向双极滤波器检测边缘,构建方向边缘检测子。以增强特征提取的鲁棒性,提升边缘检测的准确度。在此基础上,模拟大脑视觉皮质细胞对线条响应强度的反馈,根据不同边缘方向及间距,度量图像线条的空间频率。设计空间频率间距检测子,将方向边缘图像映射至方向θ-间距I坐标系中。使原图像的旋转与比例缩放,在该坐标系上表现为水平与垂直方向变化。在第2阶段中,针对第1阶段输出图像,再次进行方向边缘检测与间距检测。将第1阶段中水平与垂直平移变换,转变为第2阶段的特征图中不变像素点,使图像具有RST不变性。通过实验统计分析,验证了本文特征的RST不变性及其识别能力。并与其他不变属性特征提取方法进行了识别率与复杂度比较,突显本方法对噪声的强鲁棒性与RST的高识别率。     

An improvement of the Space-Time Image Velocimetry combined with a new denoising method for estimating river discharge

The Space-Time Image Velocimetry (STIV) is a time-averaged velocity measurement method, which takes river surface images as the analysis object, and detects the Main Orientation of Texture (MOT) in a generated Space-Time Image (STI) to obtain one-dimensional velocities on the water surface. The STIV has great potential in real-time monitoring of river flow owing to its high spatial resolution and low time complexity. However, the generated STI contains a lot of noise and interference texture, which is inevitable in practical applications. The practicality of the STIV is severely limited by the low-quality STI. To solve this problem, a denoising method based on the filtering technology is proposed and combined with different texture detection algorithms in this paper. The accuracy of this method is verified through a comparative field experiment with an impellor-style current meter. The experimental results show: (1) By using this new denoising method, the robustness and accuracy of the STIV are significantly improved no matter what kind of texture detection algorithm is adopted; (2) Among all the texture detection algorithms, the FFT-based STIV combined with the new denoising method performs best. The relative errors of the surface velocities are controlled within 6%, and the relative errors of the discharges are controlled within ±4%.     

多尺度引导滤波及其在去雾中的应用

将引导滤波与提升小波相结合提出了一种多尺度引导滤波方法,以实现在平滑图像细节的同时保持图像边缘不模糊。该方法通过提升小波法对将图像进行多尺度分解,即将信号分解成一个低频子带和多个高频子带。在提升小波重构过程中,利用引导滤波平滑每个尺度的低频信息并保持其边缘不模糊。最后,针对滤波后残余的细节,对提升小波重构后的平滑图像再次进行引导滤波,以便进一步平滑图像细节。将多尺度引导滤波应用于暗通道去雾先验理论并进行了主、客观评价。结果显示:多尺度引导滤波能够深层次平滑图像细节,保持边缘完整性,从整体上提高了图像的对比对和视觉效果,有效恢复了场景信息并保留场景的边缘信息。另外,该方法改善了客观评价指标,其对比度增强系数指标平均提升了0.1以上,场景结构相似度平均提升了1以上,而LOE(Lightness Order Error)参数降低了10以上,满足了去雾应用的视觉需求。     

Quantitative characterization of carbon/carbon composites matrix texture based on image analysis using polarized light microscope

A quantitative characteristic method was proposed for characterizing the matrix texture of carbon/carbon(C/C) composites, which determined the mechanical and physical properties of C/C composites. Based on the cloud theory that was commonly used for uncertain reasoning and the transformation between quantitative and qualitative characterization, so the relationship between the extinction angle and texture types was built by the cloud models for describing the texture of microstructure, moreover, linguistic controllers were established to analyze the matrix texture in accordance with the features of the polarized light microscope (PLM) image. On this basis, the extinction angle could be calculated from the PLM image of the C/C composites. In contrast to the results of measurement, the errors between calculative values and measured values were maintained 1–2° in basically. Meanwhile, the PLM image of C/C composites was segmented by the component, in particular, the matrix with mixed textures was further segmented by the difference of texture. It means that the quantitative characterization of C/C composites matrix based on single PLM image has been realized. Microsc. Res. Tech. 78:908–917, 2015. © 2015 Wiley Periodicals, Inc.     

A low cost 3D shape measurement method based on a strip shifting pattern

We present a simple, low cost but fast 3D shape measurement method. There is no limitation on the object's material and texture. We use a projector to project a strip shifting pattern on the object, and a digital camera to record videos of the scene. The distortion of the strip shadow on the object is used to get the object's 3D information. A novel space-time edge finding method is introduced to position the shadow edge accurately. This edge finding method overcomes the effect of inter-reflection and high light. Using this space-time information, we can calculate the pixels' 3D coordinates. To get the 3D shape of an object with black texture, we improve the black strip pattern to a 3-color strip pattern. The bad data are filtered by a post-processing 3D filter, which makes full use of the neighborhoods' geometric constraints and the view point constraint. Meanwhile, our measurement method is fast, regardless of the complexity of the shape.     

光针轮廓扫描技术测量内螺纹曲面

分析了激光光针扫描在测量内螺纹曲面时的特性及影响精度的因素。根据光斑在被测面的噪声分布特点,采用中值滤波与小波阈值去噪相结合的综合滤波算法对光斑图像进行了去噪处理,其中中值滤波可以有效地消除光斑图像中的脉冲噪声,而基于小波变换的阈值去噪算法可以消除图像中的高斯噪声。通过综合滤波算法对光斑图像进行处理,可以有效消除激光光斑噪声,消除图像噪声对测量精度的影响,同时保持了光斑图像的细部特征。根据激光光斑图像在倾斜被测物体表面光强分布特点,设计了近似圆拟合算法来确定光斑中心,该算法相对传统算法具有计算量小、计算效率高,适合在线检测的特点,可以克服测量面倾斜对激光光斑中心的影响。利用采用上述方法的坐标机激光光针扫描系统,对标准内螺纹量规进行测量,对比应用前后的测量结果,螺距精度提高了0.48 mm,中径测量精度提高了0.44 mm,牙型角精度提高0.57°。     

利用数字图像处理技术测量直齿圆柱齿轮几何尺寸

研究了采用数字图像处理技术实现对直齿圆柱齿轮几何尺寸的非接触式测量.首先对CCD摄像机拍摄的图像进行畸变校正与滤波去噪,然后对图像进行阈值分割,采用基于数学形态法的四邻域腐蚀来获得单像素宽的图像边缘.针对齿轮的边缘轮廓形状特征,运用重心法、最小二乘拟合、Bresenham画圆法和Hough变换等原理,建立了测量齿轮齿数、模数、中心孔半径、齿顶圆半径、齿根圆半径和变位系数等齿轮几何尺寸参数的测量算法.使用1280×1024的CCD摄像机及黑白采集卡对分度圆直径为50mm的直齿圆柱齿轮进行测量实验,与人工测量值对比,绝对误差小于一个像素,在各测量参数中,最大尺寸的齿顶圆半径绝对误差值为13μm.研究结果表明:因为CCD摄像设备的分辨率越高、被测物体的尺寸越小,则测量精度越高,且为线性关系,所以,使用高分辨率CCD摄像设备并配备光学放大系统,可实现对高精度和微小直齿圆柱齿轮几何尺寸参数的测量.如使用1280×1024像素以上的CCD摄像设备测量分度圆直径5mm以下的直齿圆柱齿轮时,测量精度可在2μm以下.     

Detection of pinhole defects on chips and wafers using DCT enhancement in computer vision systems

This paper presents a global approach for the automatic inspection of tiny pinhole defects in randomly textured surfaces of surface barrier layer (SBL) chips. By means of a discrete cosine transform (DCT)-based image restoration scheme, the proposed method is independent of textural features and thus not confined by the limitations of feature extraction based methods. Through properly decomposing the frequency matrix of an image in the DCT domain and selecting the best radius of the sector filter for the high-pass filtering operation, we effectively attenuate the global random texture pattern and accentuate only tiny pinhole defects in the restored image. We also develop two accumulative sum detection procedures that automatically determine the best high-pass filtering parameters based on the abrupt changes of the frequency coefficients in the decomposed matrix. Experimental results show that the proposed method outperforms the traditional approach in reducing the Type I error by 70–80% and in decreasing the deviation of the defect areas by 95%. Moreover, the proposed method can be applied to various types of passive components in large-batch production because no precise positioning of the target chip or template matching is required.     

火箭弹离轨参数测量中的图像处理方法

根据高速摄像系统在火箭弹离轨参数测量中的应用,介绍了火箭弹离轨参数测量原理,提出了帧相减、相关滤波定位、轴线自动提取等多种图像处理方法,并将这些方法应用于工程实际.实践表明,在利用帧相减和边缘跟踪技术进行粗定位的基础上,采用相关滤波技术在小区域进行定位可以减少计算量,使定位精度达到0.2个像元,而在轴线自动提取中,用灰度图像形态学边缘检测方法,可使姿态角测量精度优于0.5°.     

An accurate and robust method for the honing angle evaluation of cylinder liner surface using machine vision

This paper presents a machine vision-based method for evaluating honing angle of cylinder liners by exploring the frequency domain characteristics of cylinder liner images. An image-processing algorithm based on Fourier transform and Hough transform is developed and applied on images containing the honing texture patterns captured from 14 cylinder liners manufactured with varying honing angles. The images are captured from cylinder liner surfaces by destructive and non-destructive manner using a charge-coupled device camera attached with magnifying lenses and a miniature microscopic probe respectively.A graphical user interface-based program and protractor-based manual method are used for verifying the accuracy and consistency of the developed image-processing algorithm for automatically evaluating the honing angle from the captured images of cylinder liner surfaces. The results clearly demonstrate the efficacy of the proposed method for robustly evaluating the honing angle and it can be used by the cylinder liner manufactures for fast and accurate measurement of honing angle with a resolution of 1°.