基于数字图像处理的植物叶面积测量方法

数码相机摄入图像时产生的线性几何畸变会给叶片面积的测量带来误差。针对此问题文章改进了Hough变换算法,并用来对叶片畸变图像进行几何校正,然后计算叶片面积。实验表明,该方法适于多种植物的叶面积活体测量,速度快,精度高。     

二维不等长变换改进及其应用EI北大核心CSCD

针对二维不等长变换置乱图像效果差且纹理特征明显,难以满足高安全性图像信息保护需要的问题,提出二维不等长Arnold变换的改进方法,并将其用于像素位置置乱和像素值加密中.该方法利用经典可逆二维标准映射的构造思想将二维不等长Arnold变换进行非仿射化修改,获得一种具有非线性变换特性的保面积且具有周期的置乱变换,对任意高宽不等图像置乱加密并用其逆变换来快速恢复原图像.大量实验结果表明,文中方法是有效的,相比现有二维不等长Arnold变换能有效地改善图像置乱效果并降低图像纹理特征,对任意高宽图像的高性能置乱加密具有一定的推广价值.     

植物叶片轮廓特征提取方法研究

根据植物叶片形态特征中锯齿和叶裂的重要性,设计了基于链码的研究方法。通过对叶片图像预处理得到叶片的轮廓曲线、结合基于链码的拐点检测方法和基于链码差的边界凹凸性判别方法确定锯齿点和叶裂点、改进基于链码的目标面积计算方法计算锯齿和叶裂的面积。从锯齿和叶裂的面积和周长占整个叶片的面积和周长的比例以及叶片包含的锯齿和叶裂数三个方面对叶片进行描述。实验对3种共70张叶片提取特征,归纳特征阈值范围。实验结果表明新方法可以大大提高计算面积的精确度,并且这三个特征可以体现出不同种的植物叶片,可以作为新的特征值,为识别植物物种和分类提供帮助。     

基于运动恢复结构方法的植株三维重建

为了探究基于运动恢复结构(Structure From Motion, SFM)方法的植株三维重建模型的效果,为植物三维重建工作提供研究案例,本文以紫叶鸭跖草(setcreasea pallida)为研究对象,在搭建序列图像获取平台的基础上,选取35幅、75幅、105幅序列图像进行三维重建的对比分析;同时从植株表型参数方面,对植株三维重建模型进行精度评价。结果表明：75幅图像序列的重建效果最好;不同图像序列的模型计算的植株高度相对误差（Relative Error, RE）均小于2.5%,决定系数（coefficient of determination, R2）均大于0.998;不同图像序列的模型提取叶片长和叶片宽的RE均小于2.89%,R2均大于0.958。因此,序列图像的数量与重建模型的效果有关,但二者并非呈正相关关系;序列图像的数量对重建叶片的长与宽的误差影响较小;SFM方法应用于结构比较复杂的植株的三维重建可以取得较好的重建效果。     

基于极坐标的树木叶片特征提取方法

提出了一种在极坐标下进行特征提取的方法,并将其应用于树木叶片图像识别中。该方法首先将目标图像二值化并映射到极坐标下,提取具有旋转、缩放、平移不变性的曲线面积比率、跨度比、饱和度和高度变化率等特征。然后通过最小欧式距离对叶片进行计算、识别。该方法克服了直角坐标系下特征提取方法计算量大,花费的时间长的缺陷。基于该方法的叶片特征提取算法的时间复杂度为[O(n)]。对于叶型有区分,且需要快速进行树叶识别的树叶数据集有很好的效果。该方法在常见的13种树木叶片中进行测试,平均正确识别率达到90%以上。     

基于三维点云的植物叶片重建及其面积估算

为提高植物叶片面积测量的准确度,本文提出了一种植物叶片三维重建补偿方法。该方法首先使用多角度拍摄植物叶片的方法来获取图像;其次,通过运动恢复结构算法(SFM)、聚类多视角立体算法(CMVS)和基于面片的多视角立体算法(PMVS)处理图像并生成三维点云;然后,对点云进行去噪、分割、填补、三角网格化处理;最后,对叶片面积进行估测。实验结果表明,本文方法测量叶片面积的准确度与扫描法接近,并且能解决由于叶片重叠产生的叶面积测量不准确的问题。     

基于Snake模型的植物叶片面积计算方法

为对植物叶片面积进行准确测量,提出一种通过Snake模型提取叶片轮廓,并在叶片轮廓基础上计算面积的方法。对传统Snake模型进行改进,定义HSI空间的颜色梯度作为Snake的外部能量函数,将提取出的角点作为初始轮廓的顶点,通过自适应增加或减少顶点来设置Snake的初值。利用改进的Snake模型提取叶片轮廓,在叶片轮廓链码表的基础上计算面积。实验结果表明,与Image J软件中计算叶片面积的方法相比,该算法的测量精度更高。     

基于面积约束的大豆叶片三维建模方法

针对基于图像对大豆叶片进行三维真实感建模的问题,考虑叶面积指数对大豆产量的影响,提出一种受面积约束的三维叶片建模方法.该方法首先从二维图像中提取出叶片特征点和叶片面积,然后采用双三次均匀B样条曲面插值特征点进行建模,并且根据叶片边缘卷曲形态对网格模型进行变形,构造叶片卷曲模型,分别计算不同卷曲模型的最大光照面积,从而选择最优的模型.实验证明,该方法能构造出逼真的叶片模型,并且具有一定的生物学意义和实际应用价值.     

基于相参处理的宽脉冲信号参数估计快速算法

提出了一种宽脉冲信号参数估计快速算法,利用抽取的方法来降低宽脉冲信号参数估计的计算量。首先,对宽脉冲正弦波信号进行抽取构造相参脉冲串,利用相参脉冲频率估计算法进行频率估计。其次,对于宽脉冲线性调频信号,对其做延时相关之后即可转化为宽脉冲正弦波信号,然后在上述抽取和相参处理方法的基础上即可得到宽脉冲线性调频信号参数估计值。性能分析和仿真结果表明,该算法在保证一定的参数估计精度前提下,大大降低了算法的计算量,有利于宽脉冲信号参数估计的实时处理。     

PCB检测中圆Mark的快速精确定位

高密度电路板在缺陷检测时获取的圆形标志有时会变形,从而影响检测精度。为此,提出一种求取最圆椭圆度的Mark点精确定位算法。该算法将检测的彩色图像转换成灰度图,采用Otus的阈值分割技术使Mark区域与背景相分离,对图像进行二值化,求取边缘点(图像轮廓)。对图像轮廓进行椭圆拟合后求取椭圆的外接矩形,将矩形长与宽之差与矩形宽之比小于0.1作为判据,判断所求的是否为最圆的椭圆,输出Mark点中心。仿真测试结果表明,该算法具有高速、抗干扰能力强和鲁棒性高的特点。     

Validation of plant part measurements using a 3D reconstruction method suitable for high-throughput seedling phenotyping

In plant phenotyping, there is a demand for high-throughput, non-destructive systems that can accurately analyse various plant traits by measuring features such as plant volume, leaf area, and stem length. Existing vision-based systems either focus on speed using 2D imaging, which is consequently inaccurate, or on accuracy using time-consuming 3D methods. In this paper, we present a computer-vision system for seedling phenotyping that combines best of both approaches by utilizing a fast three-dimensional (3D) reconstruction method. We developed image processing methods for the identification and segmentation of plant organs (stem and leaf) from the 3D plant model. Various measurements of plant features such as plant volume, leaf area, and stem length are estimated based on these plant segments. We evaluate the accuracy of our system by comparing the measurements of our methods with ground truth measurements obtained destructively by hand. The results indicate that the proposed system is very promising.     

An orthogonal basis for the hyperbolic hybrid polynomial space

Motivated by the wide usage of the Tchebyshev basis and Legendre basis in the algebra polynomial space, we construct an orthogonal basis with the properties of the H-Bézier basis in the hyperbolic hybrid polynomial space, which is similar to the Legendre basis and holds remarkable properties. Moreover, we derive the transformation matrices that map the H-Bézier basis and the orthogonal basis forms into each other. An example for approximating the degree reduction of the H- Bézier curves is sketched to illustrate the utility of the orthogonal basis.     

利用矩实现植物叶片长宽的测量

叶片长宽的测量常采用旋转法,其在测量时需多次旋转叶片直至外接矩形面积最小为止,耗时较大;由于叶片形状各异,旋转法的测量准确性也不高。鉴于此,给出了运用矩测量叶片长宽的方法,用零阶矩和一阶矩求得叶片重心,通过一阶矩和二阶矩获得叶片的主轴方向,运用旋转矩阵得到叶片的最小外接矩形,将此矩形的长宽作为叶片的长宽。对122幅叶片图像进行实验,结果表明：矩的方法测量准确率是98.4%,而旋转法的准确率是37.7%。在测量过程中旋转法需多次旋转叶片,而矩的方法只需旋转两次,测量时间至少缩短了一半。总之,基于矩的方法准确性高、测量速度快。     

复杂背景中的阔叶轮廓提取技术

树叶轮廓提取是植物图像识别的一个重要环节。设计一种复杂图像分割的综合算法。首先割取图像的目标区域利用Canny算子查找目标的边缘,然后边缘集合中查找所有的连通分支,利用二阶倒数查找连通分支长度与数目的关系,最后求出线条长度阈值,保留长度比阈值大的连通分支,进而得到目标图像的边缘。以阔叶楠树树叶为例进行实验,证明该算法可行有效,能够很好地过滤到背景的噪点和页面中的纹路干扰。     

Arc length-based aspect ratio selection

The aspect ratio of a plot has a dramatic impact on our ability to perceive trends and patterns in the data. Previous approaches for automatically selecting the aspect ratio have been based on adjusting the orientations or angles of the line segments in the plot. In contrast, we recommend a simple, effective method for selecting the aspect ratio: minimize the arc length of the data curve while keeping the area of the plot constant. The approach is parameterization invariant, robust to a wide range of inputs, preserves visual symmetries in the data, and is a compromise between previously proposed techniques. Further, we demonstrate that it can be effectively used to select the aspect ratio of contour plots. We believe arc length should become the default aspect ratio selection method.     

水稻叶片形态日变化过程可视化模拟研究

在实验测定的基础上,分析了水稻叶片几何形态随逐日生长时间动态变化的规律,分别构建了叶长变化模型、叶长与叶宽关系模型、茎叶夹角变化模型、以及不同叶位最终叶长模型和叶片出叶时间模型。结合水稻叶片的三维形态模型,在计算机上编程实现了水稻叶片器官形态逐日动态生长变化过程的可视化模拟,具有较强的真实感,为构建虚拟水稻生长系统奠定了基础。     

Information systems practice, education and research

Abstract. The launch of a new journal in information systems prompts thought and debate concerning the state of the subject area and some contemplation on its past and future. This introductory paper reflects the views of the editors, views which will not be shared by all. We find a wide spectrum of interpretations and experiences concerning the nature of information systems and this wide range of views is both a strength and a weakness. It is a weakness in the sense that it is very difficult to put boundaries around the area and establish common definitions and accepted norms. The latter are usually associated with more stable and established disciplines that have accepted underlying theories. It is a strength in the sense that the wide variety of views, experiences and background subjects adds richness to the discipline. From the point of view of the Journal of Information Systems this should mean a wide variety of interesting topics from which we can draw. Our paper begins with an introduction to the debate about the nature of information systems, a debate which is continued in the following paper. We also give an overview of practice, education and research in information systems. In order to keep the paper to a reasonable length, this overview will necessarily be selective and will probably be Anglocentric.     

Estimation of vegetation water content and photosynthetic tissue area from spectral reflectance: a comparison of indices based on liquid water and chlorophyll absorption features

Because of the high water content of vegetation, water absorption features dominate spectral reflectance of vegetation in the near-infrared region of the spectrum. In comparison to indices based on chlorophyll absorption features (such as the normalized difference vegetation index (NDVI)), indices based on the water absorption bands are expected to “see” more deeply into thick canopies and have a preferential sensitivity to thin as opposed to thick tissues. These predictions are based on the much lower absorption coefficients for water in the short wavelength water bands as compared to chlorophyll. Thus, the water bands may have advantages over NDVI for remote sensing of photosynthetic tissues. Previous studies have primarily related water band indices (WI) to leaf area index (LAI). Here we expand the definition of photosynthetic tissues to include thin green stems and fruits and measure a wide range of species to determine the influence of variable tissue morphologies and canopy structures on these relationships. As expected, indices based on reflectance in the water absorption bands in the near infrared were best correlated with the water content of thin tissues (less than 0.5-cm thickness). The choice of wavelength for a water index was much more important for thick than for thin canopies, and the best wavelengths were those where water absorptance was weak to moderate. We identified three wavelength regions (950-970, 1150-1260 and 1520-1540 nm) that produced the best overall correlations with water content. Comparison of these wavelength regions with the atmospheric “windows” where water vapor absorption is minimal suggests that the 1150-1260 and 1520-1540 nm regions would be the best wavelengths for satellite remote sensing of water content. We also developed and tested a new Canopy Structure Index (CSI) that combines the low absorptance water bands with the simple ratio vegetation index (SR) to produce an index with a wider range of sensitivity to photosynthetic tissue area at all canopy thicknesses. CSI was better than either WI or SR alone for prediction of total area of photosynthetic tissues. However, SR was best for prediction of leaf area when other green tissues were excluded. All of these relationships showed good generality across a wide range of species and functional types.     

Mexitl: Multimedia in Executable Interval Temporal Logic

This paper explores a formalism for describing a wide class of multimedia document constraints, based on an interval temporal logic. We describe the requirements that arise from the multimedia documents application area, and we illustrate these requirements using several examples. Then we present the temporal logic formalism that we use. This logic extends existing interval temporal logic with a number of new features: actions, framing of actions, past operators, a projection-like operator called filter and a new handling of interval length. The notation is applied to the specification of the examples, and in particular a set of logical manipulations, providing feedback to an author, is presented. A model theory, logic and satisfaction relation are defined for the notation.     

基于叶片形态特征的葡萄品种自动识别

葡萄在全世界种植范围较广,葡萄品种识别对葡萄资源统计、新品种鉴定及遗传资源保护都有重要意义。以成熟叶片为基本材料,不变矩、面积、周长、主叶脉长度和叶柄长度等11维特征向量为基础数据,采用叶片特征选择、图像处理、特征值提取、建立分类模型等方法,运用国际葡萄与葡萄酒组织形态分类方法和改进的欧式距离等技术开发一个基于葡萄叶片数字图像的葡萄品种自动识别软件。共测试17种酿酒和3种野生葡萄,识别率达87%。该方法具有自动化、识别速度快、花费低、省时省力等特点,可应用于葡萄病虫害的识别、杂交新品种双亲的判定等。