边缘检测中的改进型均值滤波算法

针对传统高斯滤波器算法存在边缘模糊及局部伪影的问题,提出一种改进型均值滤波算法,以有效去除图像中的高密度脉冲噪声。通过求解图像直方图,检测图像直方图的左右2个峰值点,以查找出可疑的噪声点,进而使用灰度值确定其坐标。利用图像像素点周围灰度值的相似性,在局部窗口选择递归加权平均值代替被污染的图像像素点灰度值。结合自动选择Canny算子的双阈值方法,对灰度图像边缘进行检测。实验结果表明,该算法的算子滤波效果优于LOG算子和传统灰度Canny算子,且具有较好的稳定性。     

基于直方图均衡化的Robinson图像边缘检测算法

针对图像边缘检测,现有Robinson相关算法存在效率低、阈值设定随机性大、易出现伪边缘等问题,提出一种改进Robinson的图像边缘检测算法;该算法利用直方图均衡化对图像进行增强,然后将Robinson算子原有的八方向梯度依照两两垂直原则组合为八组,分别计算每组梯度的范数,并取其最大值作为该像素点的梯度;最后取整幅图像的灰度均值作为阈值来识别图像的边缘像素和背景像素;实验表明,相对于现有相关算法,该算法检测结果更加清晰完整,同时避免了传统算子人为设定阈值随机性大的问题。     

基于局部空间像素特征的自适应加权滤波算法

提出了一种新的基于局部空间像素特征的椒盐噪声自适应加权滤波算法。该算法首先对含噪图像逐点进行噪声检测,把所有像素分为含噪像素点和信号像素点;然后采用自适应加权滤波方法,对检测到的噪声点进行滤波,滤波权重由确定的数学公式来确定,自适应于滤波窗内临近像素的局部特征。实验结果表明,该算法不仅可以有效地除去椒盐噪声,又可以较好地保持图像边缘细节,尤其在噪声密度较大时,效果明显优于传统的中值滤波算法。     

基于阈值的数字图像去噪的算法研究

提出了一种基于阈值的数字图像去噪算法。该算法根据椒盐噪声的特点,通过设置阈值,当待处理像素点的灰度值与该点周围像素点的均值的差小于阈值时,该像素点不作处理,否则就用该点周围像素点的均值代替该点的值。同时,研究分析了图像去噪最佳阈值与图像的平均值、方差、熵以及复杂度之间的关系,以便为快速寻找最佳阈值提供理论根据。实验仿真表明,与其他去噪算法相比,该算法既能较好地去除噪声,同时不会使图像变得模糊。     

基于平稳小波变换邻域系数萎缩的图像去噪法

为消除图像去噪过程中普遍存在的边缘失真,先利用Canny边缘检测算子提取含噪图像的边缘特征,使边缘图像的像素点和含噪图像的像素点一一对应,将含噪图像中边缘像素点的值设零,再将得到的去掉边缘信息的含噪图像进行二维离散平稳小波变换,对小波系数采用基于邻域的方法进行系数萎缩.该算法充分考虑了平稳小波系数的邻域性质,对处理后的小波系数进行平稳小波反变换得到平滑去噪图像,最后将边缘图像嵌入平滑图像中得到去噪后的图像.该算法能够在去除噪声的同时较好地保护图像的边缘,是一种有效的图像去噪法.     

一种图像亚像素边缘检测算法的改进研究

为了提高刀具预调测量仪的检测精度,提出了一种改进的图像快速亚像素边缘检测算法——基于正交多项式拟合的亚像素边缘检测算法。首先,利用传统的Sobel算子完成边缘点整像素级别的检测,确定边缘的主体区域;然后,过边缘点沿边缘法线方向拓展像素,取一系列像素点并计算其灰度值;最后根据像素点灰度分布的数学特征,利用正交多项式和最小二乘法求拟合函数,通过拟合曲线确定图像边缘点的精确位置,实现图像亚像素边缘检测。实验证明,该算法运行时间短,约为0.63 s;检测精度高,可达0.1 pixels。     

新的噪声污染灰度图像边缘检测统计方法*

针对传统算子进行边缘检测时易丢失边缘信息和在非边缘处增强噪声的缺陷,提出一种基于非参数变点统计分析的噪声图像边缘检测方法,该统计方法不但不需要图像数字特征的任何先验信息,而且对噪声污染的图像不作任何滤波处理.实验结果表明,提出的算法优于Sobel算子,并能抑制信噪较低的高斯噪声和密度较高的椒盐噪声对分割结果的影响,是一种有效的噪声污染灰度图像边缘检测方法.     

结合修剪均值与高斯加权中值滤波的图像去噪算法

为快速准确地滤除图像中的脉冲噪声并较好地保持图像的纹理细节和边缘结构,提出一种基于修剪均值与高斯加权中值滤波的图像去噪算法。根据脉冲噪声的灰度特征与统计特征,以局部统计方式进行噪声检测,将灰度取最小值或最大值且与邻域像素相关性较小的像素识别为噪声像素。对于图像平滑区域和细节区域中的噪声像素,使用自适应修剪均值和高斯加权中值滤波算法进行去噪处理。实验结果表明,该算法在视觉效果、峰值信噪比、结构相似性及计算速度上均优于对比算法,并且能够在彻底滤除噪声的同时,较好地保持图像的纹理细节和边缘结构。     

融合多尺度边缘检测的小波贝叶斯SAR图像滤波

针对实测的SAR图像被噪声广泛淹没、传统滤波方法易模糊边缘等问题,提出了一种新的滤波方法。该方法在图像多尺度的小波分量上,将基于贝叶斯理论对不同系数和不同方向上设置不同阈值得到消噪后的各分量与基于多尺度边缘检测提取的图像边缘等结构所对应小波分量加权融合,重构输出。以真实的SAR影像进行对比实验后,选取图像的均值、等效视数、边缘保持指数、信噪比及特征地物的像素灰度曲线作为评价指标,对不同的滤波方法进行了综合量化评价。实验结果表明,该方法抑制SAR图像斑点噪声的效果较好,对边缘有较好的保持效果。     

邻域统计检测的双树复小波图像去噪

针对现有的脉冲噪声去除算法在去噪性能和计算效率上的缺陷,提出了基于邻域统计检测的双树复小波图像去噪算法。根据噪声的灰度特征、邻域像素的多数原则以及灰度偏差等统计特性进行噪声检测,充分利用双树复小波变换的优秀特性,在双树复小波域中用光滑可导的阈值函数以及自适应阈值对噪声图像进行去噪处理,最后用去噪图像中的像素,替换噪声图像中对应的噪声像素以得到最终的去噪图像。实验数据证明,所提出的方法优于部分最新提出的算法,具有较好的去噪性能和快速的计算效率。     

European Community policy and the market

Abstract This paper starts with some reflections on the policy considerations and priorities which are shaping European Commission (EC) research programmes. Then it attempts to position the current projects which seek to capitalise on information and communications technologies for learning in relation to these priorities and the apparent realities of the marketplace. It concludes that while there are grounds to be optimistic about the contribution EC programmes can make to the efficiency and standard of education and training, they are still too technology driven.     

一种自适应子融合集成多分类器方法

融合集成方法已经广泛应用在模式识别领域,然而一些基分类器实时性能稳定性较差,导致多分类器融合性能差,针对上述问题本文提出了一种新的基于多分类器的子融合集成分类器系统。该方法考虑在度量层融合层次之上通过对各类基多分类器进行动态选择,票数最多的类别作为融合系统中对特征向量识别的类别,构成一种新的自适应子融合集成分类器方法。实验表明,该方法比传统的分类器以及分类融合方法识别准确率明显更高,具有更好的鲁棒性。     

Explanation and prediction: an architecture for default and abductive reasoning

Although there are many arguments that logic is an appropriate tool for artificial intelligence, there has been a perceived problem with the monotonicity of classical logic. This paper elaborates on the idea that reasoning should be viewed as theory formation where logic tells us the consequences of our assumptions. The two activities of predicting what is expected to be true and explaining observations are considered in a simple theory formation framework. Properties of each activity are discussed, along with a number of proposals as to what should be predicted or accepted as reasonable explanations. An architecture is proposed to combine explanation and prediction into one coherent framework. Algorithms used to implement the system as well as examples from a running implementation are given.     

Three Process Perspectives: Organizations, Teams, and People

This paper provides the author's personal views and perspectives on software process improvement. Starting with his first work on technology assessment in IBM over 20 years ago, Watts Humphrey describes the process improvement work he has been directly involved in. This includes the development of the early process assessment methods, the original design of the CMM, and the introduction of the Personal Software Process (PSP)^SM and Team Software Process (TSP){^SM}. In addition to describing the original motivation for this work, the author also reviews many of the problems he and his associates encountered and why they solved them the way they did. He also comments on the outstanding issues and likely directions for future work. Finally, this work has built on the experiences and contributions of many people. Mr. Humphrey only describes work that he was personally involved in and he names many of the key contributors. However, so many people have been involved in this work that a full list of the important participants would be impractical.     

基于复小波噪声方差显著修正的SAR图像去噪

提出了一种基于复小波域统计建模与噪声方差估计显著性修正相结合的合成孔径雷达(Synthetic Aperture Radar,SAR)图像斑点噪声滤波方法。该方法首先通过对数变换将乘性噪声模型转化为加性噪声模型,然后对变换后的图像进行双树复小波变换(Dualtree Complex Wavelet Transform,DCWT),并对复数小波系数的统计分布进行建模。在此先验分布的基础上,通过运用贝叶斯估计方法从含噪系数中恢复原始系数,达到滤除噪声的目的。实验结果表明该方法在去除噪声的同时保留了图像的细节信息,取得了很好的降噪效果。     

How do children do mathematics with LOGO?

Abstract  This paper considers some results of a study designed to investigate the kinds of mathematical activity undertaken by children (aged between 8 and 11) as they learned to program in LOGO. A model of learning modes is proposed, which attempts to describe the ways in which children used and acquired understanding of the programming/mathematical concepts involved. The remainder of the paper is concerned with discussing the validity and limitations of the model, and its implications for further research and curriculum development.     

Editorial: Special issue on recent advances in hybrid control theory and applications

正The demands of a rapidly advancing technology for faster and more accurate controllers have always had a strong influence on the progress of automatic control theory.In recent years control problems have been arising with increasing frequency in widely different areas,which cannot be addressed using conventional control techniques.The principal reason for this is the fact that a highly competitive economy is forcing systems to operate in regimes where     

Information for Authors

正Aim The Journals of Zhejiang University-SCIENCE(A/B/C)areedited by the international board of distinguished Chinese andforeign scientists,and are aimed to present the latest devel-opments and achievements in scientific research in China andoverseas to the world’s scientific circles,especially to stimulateand promote academic exchange between Chinese and for-eign scientists everywhere.     

Enhancing a leaf radiative transfer model to estimate concentrations and in vivo specific absorption coefficients of total carotenoids and chlorophylls a and b from single-needle reflectance and transmittance

The relative concentrations of different pigments within a leaf have significant physiological and spectral consequences. Photosynthesis, light use efficiency, mass and energy exchange, and stress response are dependent on relationships among an ensemble of pigments. This ensemble also determines the visible characteristics of a leaf, which can be measured remotely and used to quantify leaf biochemistry and structure. But current remote sensing approaches are limited in their ability to resolve individual pigments. This paper focuses on the incorporation of three pigments—chlorophyll a, chlorophyll b, and total carotenoids—into the LIBERTY leaf radiative transfer model to better understand relationships between leaf biochemical, biophysical, and spectral properties.Pinus ponderosa and Pinus jeffreyi needles were collected from three sites in the California Sierra Nevada. Hemispheric single-leaf visible reflectance and transmittance and concentrations of chlorophylls a and b and total carotenoids of fresh needles were measured. These data were input to the enhanced LIBERTY model to estimate optical and biochemical properties of pine needles. The enhanced model successfully estimated reflectance (RMSE = 0.0255, BIAS = 0.00477, RMS%E = 16.7%), had variable success estimating transmittance (RMSE = 0.0442, BIAS = 0.0294, RMS%E = 181%), and generated very good estimates of carotenoid concentrations (RMSE = 2.48 µg/cm², BIAS = 0.143 µg/cm², RMS%E = 20.4%), good estimates of chlorophyll a concentrations (RMSE = 10.7 µg/cm², BIAS = − 0.992 µg/cm², RMS%E = 21.1%), and fair estimates of chlorophyll b concentrations (RMSE = 7.49 µg/cm², BIAS = − 2.12 µg/cm², RMS%E = 43.7%). Overall root mean squared errors of reflectance, transmittance, and pigment concentration estimates were lower for the three-pigment model than for the single-pigment model. The algorithm to estimate three in vivo specific absorption coefficients is robust, although estimated values are distorted by inconsistencies in model biophysics. The capacity to invert the model from single-leaf reflectance and transmittance was added to the model so it could be coupled with vegetation canopy models to estimate canopy biochemistry from remotely sensed data.     

Mr. Twinn’s bombes

This article discusses the history and design of the special versions of the bombe key-finding machines used by Britain’s Government Code & Cypher School (GC&CS) during World War II to attack the Enigma traffic of the Abwehr (the German military intelligence service). These special bombes were based on the design of their more numerous counterparts used against the traffic of the German armed services, but differed from them in important ways that highlight the adaptability of the British bombe design, and the power and flexibility of the diagonal board. Also discussed are the changes in the Abwehr indicating system that drove the development of these machines, the ingenious ways in which they were used, and some related developments involving the bombes used by the U.S. Navy’s cryptanalytic unit (OP-20-G).