Curve length estimation based on cubic spline interpolation in gray-scale images

This paper deals with a novel local arc length estimator for curves in gray-scale images.The method first estimates a cubic spline curve fit for the boundary points using the gray-level information of the nearby pixels,and then computes the sum of the spline segments’lengths.In this model,the second derivatives and y coordinates at the knots are required in the computation;the spline polynomial coefficients need not be computed explicitly.We provide the algorithm pseudo code for estimation and preprocessing,both taking linear time.Implementation shows that the proposed model gains a smaller relative error than other state-of-the-art methods.     

森林过火面积的遥感测算方法

根据对近年来多次特大森林火灾和相应的气象卫星资料的分析,提出利用NOAA/AVHRR数据测算森林大火的过火面积的四种方法,即灰度修正像元法、植被修正像元法、坐标法和蔓延法。在GIS地面信息数据库支持下,利用这4种方法能准确、快速地计算出过火面积。经今春应急评估试运行验证,森林大火过火面积测算精度达90%。     

基于给定精度的空间B样条曲线弧长分段点求取方法

对B样条等参数曲线按弧长精确分段,是沿曲线路径加工、检测中的一个重要问题。通过对B样条曲线弧长计算方法以及弧长计算误差与分段精度的关系进行分析,通过建立弧长分段点搜索区间及弧长二分法确定符合精度要求的弧长分段点。实验证明该方法是解决参数曲线弧长精确分段的有效方法。     

曲线插值的一种保凸细分方法

为了弥补以四点插值细分方法为代表的线性细分方法在形状控制方面的缺陷,提出一种基于几何的插值型保凸细分方法.细分过程每一步中,每条边所对应的新控制顶点由原控制顶点及其切向共同确定;每点处的切向由其邻近的点所确定,并且随细分过程逐步调整.理论分析表明,该方法的极限曲线是G1连续的保凸曲线.如果所有的初始点取自圆弧段,则极限曲线就是该圆弧段.数值实例表明,采用文中方法得到的曲线较为光顺.     

Intrinsic spline curve with local control

A new spline algorithm that uses arc length as parameter and generates a curve in terms of the quantities ‘relative curvature’ and ‘relative torsion’ is described. The tangent and curvature vectors at each datapoint are estimated and the spline is built up span by span. This allows local changes without affecting the whole curve and facilitates the incorporation of derivative discontinuities. Unless discontinuities are specifically requested, the solution obtained is curvature continuous.     

空间曲线基于内在几何量的高质量采样和B样条拟合

为解决均匀参数采样在许多情况下得到质量不高的采样点,进而生成不理想的B样条拟合曲线,提出空间曲线基于内在几何量的均匀采样方法,以获得给定总数且具有代表性的采样点.首先定义基于弧长、曲率和挠率加权组合的特征函数,通过调整组合参数更好匹配不同的曲线形状;然后提出空间曲线基于内在几何量的自适应采样方法,迭代生成满足给定距离阈值的采样点.采用最大绝对误差和均方根误差作为评价指标,与均匀弧长采样方法和基于弧长和曲率平均的均匀采样方法进行对比,并通过实例进行验证.结果表明,文中方法在采样质量和B样条拟合结果上获得明显改善.     

基于支持向量机的椒盐噪声去除方法

针对自然图像中相邻像素的相关性及其椒盐噪声的特点,提出了一种基于支持向量机的椒盐噪声消除方法。该方法应用支持向量机的学习机制对图像灰度曲面进行最佳拟合,并从训练样本中提取支持向量与相应的决策函数,最后根据决策函数在拟合曲面上进行噪声像素点的灰度值预测,从而恢复噪声点的原始信号。通过与传统的中值滤波和均值滤波进行实验对比,提出的方法可有效地去除椒盐噪声,同时最大限度地保留图像的细节信息,尤其对高密度椒盐噪声图像的处理效果更为理想。     

一种椭圆生成的最优算法*

首先对椭圆线构造一个带域,并证明在此带域中所确定的像素点是误差最小的。应用带域提出了一种误差最小的椭圆生成算法,得到递推公式,每次要计算的是朝X方向或Y方向取像素点的个数,跟过去一贯采用的每生成一个像素点都要计算判别函数的传统方法比较,具有较强的优越性,尤其是对长轴与短轴相差越大的椭圆优越性越明显,最后给出了计算实例。     

基于流体静力学的区域分割活动轮廓模型

提出一种新的活动轮廓模型,应用于灰度图像的区域分割。对于定义在灰度图像 上的闭合连续简单曲线,该模型应用流体静力学理论直接驱动,使其不断地缓慢收拢,直至收 敛于区域边界。在这个过程中,闭合连续简单曲线所经历的像素都被该模型根据像素性质判定 其区域归属。重新初始化有关变量,激活已收敛于区域边界的闭合连续简单曲线,继续驱动闭 合连续简单曲线收拢,直至该曲线收敛于内嵌的新区域边界或者收敛于一个点。在该模型运行 过程中,一条闭合连续简单曲线可能会分裂成多条闭合连续曲线,以适应多区域分割。当一条 闭合连续的简单曲线经过模型持续驱动之后收敛于一个点时,被其包围的区域分割才告结束。 本文提出的模型能够分割多区域和嵌套区域。     

自适应滤波窗实现距离加权图像椒盐噪声滤除

目的 在比较几种椒盐去噪方法的滤波窗口尺寸选择策略的基础上,提出一种基于自适应滤波窗的距离加权图像椒盐噪声滤除方法。方法 首先将图像中灰度值为0或255的像素点判定为噪声点,接着对每个噪声点,在以该噪声点为中心、不断增大面积的滤波窗口序列中,寻找包含非噪声点的最小尺寸窗口。若此窗口尺寸小于预设的阈值,则使用该窗口中的非噪声点进行距离加权滤波。否则认为该噪声点位置位于图像自身灰度值为0或255的像素点区域内部,使用少数服从多数策略计算灰度恢复值。结果 将本文方法与其他7种椒盐去噪方法相比较。当图像自身包含较多灰度值为0或255的像素点时,本文方法去噪效果优于其他7种方法。当图像自身不含或较少包含灰度值为0或255的像素点时,本文方法与其他方法中的最优去噪结果效果相当。结论 本文方法不仅能够有效滤除椒盐噪声,而且适用于自身包含灰度值为0或255的像素点多的椒盐噪声图像。     

Point-tangent/point-normal B-spline curve interpolation by geometric algorithms

We introduce a novel method to interpolate a set of data points as well as unit tangent vectors or unit normal vectors at the data points by means of a B-spline curve interpolation technique using geometric algorithms. The advantages of our algorithm are that it has a compact representation, it does not require the magnitudes of the tangent vectors or normal vectors, and it has C² continuity. We compare our method with the conventional curve interpolation methods, namely, the standard point interpolation method, the method introduced by Piegl and Tiller, which interpolates points as well as the first derivatives at every point, and the piecewise cubic Hermite interpolation method. Examples are provided to demonstrate the effectiveness of the proposed algorithms.     

A spatial–spectral kernel-based approach for the classification of remote-sensing images

Classification of remotely sensed images with very high spatial resolution is investigated. The proposed method deals with the joint use of the spatial and the spectral information provided by the remote-sensing images. A definition of an adaptive neighborhood system is considered. Based on morphological area filtering, the spatial information associated with each pixel is modeled as the set of connected pixels with an identical gray value (flat zone) to which the pixel belongs: The pixel's neighborhood is characterized by the vector median value of the corresponding flat zone. The spectral information is the original pixel's value, be it a scalar or a vector value. Using kernel methods, the spatial and spectral information are jointly used for the classification through a support vector machine formulation. Experiments on hyperspectral and panchromatic images are presented and show a significant increase in classification accuracies for peri-urban area: For instance, with the first data set, the overall accuracy is increased from 80% with a conventional support vectors machines classifier to 86% with the proposed approach. Comparisons with other contextual methods show that the method is competitive.     

Simulative Measurement of Besetting Bars for Interior Decoration

Generation of besetting bars for interior decoration by means of 3-D scanning is presented Cross-section of besetting bars (the arc length of element's boundary curve) and the trail of element's movement (locus) is simulatively measured by using an arc interpolation algorithm in vector form.     

Fingerprint image mosaicking by recursive ridge mapping.

To obtain a large fingerprint image from several small partial images, mosaicking of fingerprint images has been recently researched. However, existing approaches cannot provide accurate transformations for mosaics when it comes to aligning images because of the plastic distortion that may occur due to the nonuniform contact between a finger and a sensor or the deficiency of the correspondences in the images. In this paper, we propose a new scheme for mosaicking fingerprint images, which iteratively matches ridges to overcome the deficiency of the correspondences and compensates for the amount of plastic distortion between two partial images by using a thin-plate spline model. The proposed method also effectively eliminates erroneous correspondences and decides how well the transformation is estimated by calculating the registration error with a normalized distance map. The proposed method consists of three phases: feature extraction, transform estimation, and mosaicking. Transform is initially estimated with matched minutia and the ridges attached to them. Unpaired ridges in the overlapping area between two images are iteratively matched by minimizing the registration error, which consists of the ridge matching error and the inverse consistency error. During the estimation, erroneous correspondences are eliminated by considering the geometric relationship between the correspondences and checking if the registration error is minimized or not. In our experiments, the proposed method was compared with three existing methods in terms of registration accuracy, image quality, minutia extraction rate, processing time, reject to fuse rate, and verification performance. The average registration error of the proposed method was less than three pixels, and the maximum error was not more than seven pixels. In a verification test, the equal error rate was reduced from 10% to 2.7% when five images were combined by our proposed method. The proposed method was superior to other compared methods in terms of registration accuracy, image quality, minutia extraction rate, and verification.     

Isometric Piecewise Polynomial Curves

The main preoccupations of research in computer-aided geometric design have been on shape-specification techniques for polynomial curves and surfaces, and on the continuity between segments or patches. When modelling with such techniques, curves and surfaces can be compressed or expanded arbitrarily. There has been relatively little work on interacting with direct spatial properties of curves and surfaces, such as their arc length or surface area. As a first step, we derive families of parametric piecewise polynomial curves that satisfy various positional and tangential constraints together with arc-length constraints. We call these curves isometric curves. A space curve is defined as a sequence of polynomial curve segments, each of which is defined by the familiar Hermite or Bézier constraints for cubic polynomials; as well, each segment is constrained to have a specified arc length. We demonstrate that this class of curves is attractive and stable. We also describe the numerical techniques used that are sufficient for achieving real time interaction with these curves on low-end workstations.     

拱序列的曲线描述与匹配

目的 曲线匹配是计算机视觉和图像处理中的一个重要问题;判定几何图形形状相似性,得到与人类认知一致的结果,是目前的曲线描述与分类算法不能很好解决的问题。针对曲线匹配和几何图形形状的相似性判定,提出一种有效快速的基于拱序列的曲线匹配与相似性判定算法。方法 提取曲线的角点,将曲线表示为一连串相互重叠的拱序列。对于拱序列中的每一个拱,使用拱描述子进行描述。利用拱描述子,使用动态规划方法,实现对拱序列的匹配和相似性判定。结果 为了验证本文算法,将基于拱序列的曲线描述与匹配方法应用于轮廓的拼接与几何图形的相似性比较。在轮廓拼接实验中,基于拱序列的曲线描述与匹配方法准确完成碎片轮廓的拼接和地图轮廓的拼接。在几何图形相似性的交叉度量实验中,基于拱序列的曲线描述与匹配方法可以准确反映出图形的相似程度,正确判断两幅图像是否属于同一类型。在判定不同相似程度的形状对的实验中,本文算法可以给出与人类判断相同的结果,相比较基于链码特征、多尺度不变量、形状上下文和GCT（geometry complex transform）变换算法,本文算法的距离值更好地反映出图像的相似程度。结论 理论和实验表明,该算法可有效地描述曲线、匹配曲线,及准确判断几何图形的相似性,给出与人类视觉判定一致的结果。该算法可用于基于轮廓的图像拼接和几何图形相似性的判定。     

基于角度不变的线阵推扫式CCD相机几何畸变在轨检校方法

对航天遥感相机进行在轨检校,是提高卫星产品质量,扩大产品应用效果的重要技术内容.文中研究了一种基于角度不变的线阵推扫式CCD相机几何畸变在轨检校方法.该方法利用相机外方元素对于相机视向量夹角角度影响比较小的原理,根据地面控制点和一级产品图像,求解相机视向量夹角,从中提取相机光学部件的畸变模型参数,从而实现相机内外方元素解耦.相机畸变模型采用一维3阶多项式,对焦距和主点等引起的低阶误差能够很好地吸收.该方法用在HJ-1A/B卫星的宽幅盖CCD相机几何畸变校正上,检校误差残留在2—6个像元,和参考数据精度相似,表明取得了很好的校正效果.     

参数曲线近似弧长参数化的插值方法

本文提出了参数曲线近似弧长参数化的一种插值方法。参数曲线的弧长函数的单调增的，近似弧长参数化可以转化为弧长函数的保单调分段有理线性插值。用这种插值得到的近似弧长参数化曲线插值原曲线上的一组点，最后，两个实例表明了近似弧长参数化曲线能很好地逼近原曲线，且没有所不希望的波动。     

最小加权熵支撑树图像边缘提取方法

提出了一种新的彩色图像边界提取的方法,以色彩图像直方图中搜索到的峰值作为聚类中心,根据彩色图像像素结构的特点,首先计算区域内相邻像素点之间对应的向量的欧式距离,然后构造该区域内的最小支撑树,计算相应的加权熵值确定分割阈值,最后结合向量排序统计,将排序的结果按照灰度值进行分类进行输出,实验证明了这种方法的有效性。