手绘图风格的三维模型线条渲染

现有的三维模型线条渲染方法,由于模型是网格结构,渲染得到线条图由大量的小线段组成,导致图形中有许多明显的棱角和孤立线段.提出了一种新的手绘图风格的三维模型线条渲染方法,将观察到的三维模型转化成简洁、自然的线条图.算法首先采用Suggestive Contours方法得到模型的特征线段集,通过分析线段的空间信息,将小线段连接成若干长线条,并用三次B样条曲线插值这些线条,然后引入B样条小波对线条进行简化.实验结果表明,本文的方法可以很好地连接这些线段集,得到平滑、简洁的手绘风格模型线条图.     

基于定向滤波的水墨图像线条渲染方法仿真

针对当前水墨图像线条渲染运行时间长、分辨率低的问题,提出基于定向滤波的水墨图像线条渲染方法.首先利用滤波函数对水墨图像进行去噪,可以得到经过去噪后的图像坐标,再利用Lab彩色模型对水墨图像做分割处理,根据聚类方法完成对图像的聚类处理,按照浮点方法将彩色水墨图像转为灰度图像,结合直方图阈值法将灰度图像转为二值图像,通过对水墨图像的去噪、分割以及预处理,完成了对水墨图像的轮廓提取,为图像线条渲染做准备.其次,利用水墨图像像素在RGB中的分量,计算输出和输入水墨图像间的关系,完成对水墨图像颜色的提取以及均一化处理.最后利用定向滤波方法计算水墨图像的相位偏移序列,对水墨图像正交滤波核的基函数进行求解,最终实现了对水墨图像线条的渲染.实验结果表明,在对水墨图像线条进行渲染时,提出方法不仅运行时间短、效率高,还具有较高的图像分辨率,图像的渲染效果较好.     

基于定向滤波的水墨图像线条渲染方法仿真

针对当前水墨图像线条渲染运行时间长、分辨率低的问题,提出基于定向滤波的水墨图像线条渲染方法.首先利用滤波函数对水墨图像进行去噪,可以得到经过去噪后的图像坐标,再利用Lab彩色模型对水墨图像做分割处理,根据聚类方法完成对图像的聚类处理,按照浮点方法将彩色水墨图像转为灰度图像,结合直方图阈值法将灰度图像转为二值图像,通过对水墨图像的去噪、分割以及预处理,完成了对水墨图像的轮廓提取,为图像线条渲染做准备.其次,利用水墨图像像素在RGB中的分量,计算输出和输入水墨图像间的关系,完成对水墨图像颜色的提取以及均一化处理.最后利用定向滤波方法计算水墨图像的相位偏移序列,对水墨图像正交滤波核的基函数进行求解,最终实现了对水墨图像线条的渲染.实验结果表明,在对水墨图像线条进行渲染时,提出方法不仅运行时间短、效率高,还具有较高的图像分辨率,图像的渲染效果较好.     

基于特征流的抽象线条画绘制

为了将照片图像转换为具有一定艺术美感的线条画图像,文中设计了3种基于特征流的各向异性滤波器:FGsD滤波器、FGaD滤波器和FLSM滤波器.这些滤波器的主要任务是提取图像的边缘信息,并将其显示为光滑连续的风格化线条.前两种滤波器是在分析数字图像中基于一阶微分和二阶微分边缘检测算法的性能后,将高斯一阶导滤波结果和高斯差分滤波结果进行适当的混合作为边缘检测的微分响应,然后对混合的微分响应值进行柔和阈值化处理提取边缘点.第3种滤波器是专门针对图像中的线型边结构提出的,通过计算局部亮度相似度质量来判断该像素是否属于边缘点.如果将FGsD滤波结果和FLSM滤波结果进行叠加,还可以得到明暗对比度增强的抽象线条画效果.与已有的线条画绘制算法相比,采用文中算法所生成的线条画视觉特征更鲜明、风格化效果更突出、艺术表现力更强烈.     

基于自相似的风格化线条纹理合成方法

针对动画风格化线条渲染中需要权衡线条纹理滑动和线条纹理缩放两种不同的走样现象,提出了一种新的线条纹理(自相似样图),从而避免了这两种走样现象。自相似样图的纹理可以连续地无限放大,并且可以从单一样本自动生成。自相似样图可替代传统笔画纹理用于2D插图和动画。此外,自相似样图应用新的简单的方法,可以连贯地渲染3D路径,适用于交互式应用程序。     

基于UE4的建筑模型卡通风格化渲染方法的研究

随着建筑可视化技术需求的不断提高,根据不同设计任务,建筑设计人员除需搭建写实风格建筑模型外,还有搭建诸如卡通风格等风格化建筑模型的需求。本文借助UE4引擎强大的实时渲染能力与图像后处理能力,提出通过UE4引擎后处理的方式实现三维建筑模型的卡通风格化渲染。文中对卡通风格渲染的特点以及主要实现方式进行总结,对常用的几种卡通风格渲染算法进行对比研究,并针对现有算法在处理图像边缘检测与分段渲染时存在的问题提出优化方案,引入分布式云渲染的方式提高渲染速度。通过对渲染结果的对比分析,优化后算法有效解决了现有描边算法易产生的边缘断裂问题和分段渲染算法易产生的材质、光照计算错误问题,提高了渲染质量。     

融合阴影图和深度划分阴影体的阴影渲染算法

阴影图算法可以简单、快速地渲染硬阴影,但该算法渲染的硬阴影会在边缘区域出现锯齿状走样。受此影响,基于阴影图算法渲染的柔和阴影,在小尺寸半影区域依然可能会出现锯齿状走样。因此,要渲染无走样的柔和阴影,需要精确计算阴影边缘区域的着色点对点光源的可见性。深度划分阴影体算法可以精确地计算着色点对点光源的可见性,但其不仅在效率上不及阴影图算法,还无法实现柔和阴影渲染。针对上述问题,提出一种融合阴影图和深度划分阴影体的阴影渲染算法,对处于阴影边缘区域的着色点,使用深度划分阴影体算法精确计算该着色点对点光源的可见性;对其他着色点,使用阴影图算法快速计算该着色点对点光源的可见性。最后,将着色点的可见性值存储在可见性图中并滤波即可实现无走样柔和阴影的渲染。     

GPU上的非侵入式风格化渲染

提出一种基于硬件加速的算法,在实时图形应用中非侵入式地获得各种风格化渲染特效.通过实时地截获OpenGL API函数调用,修改了常规的渲染流程.该算法完全采用硬件加速的方法,在图形处理器中对颜色缓冲区和深度缓冲区进行后处理;同时采用OpenGL绘制语言作为高级绘制语言,从而可以和其他硬件加速算法（如置换式贴图、矩阵调色盘变形等）完全兼容.实验结果表明：文中算法适用于交互式非真实感渲染的应用,可以作为一种风格化渲染的强有力的工具.     

基于线条画的2.5D卡通模型

在卡通设计中,为了通过少量的2D视图生成卡通对象任意方向的视图,形成类似对象旋转的3D效果,提出一种基于线条画输入的2.5D卡通模型.基于正交的2个视线方向上卡通对象的线条画,把其中的笔画表示为2.5D结构并进行分类,然后根据笔画的类别分别用形状插值或类比的方法生成新的形状;用画家算法结合分组的方法判断笔画的可见性,以自动生成2个输入方向中任意方向的视图.实验结果表明,该模型减少了对特定绘画程序的依赖,在中间视图的质量上比已有方法有很大提高.     

综合几何信息的实时线绘制算法

以三维网格模型的微分几何信息为依据,结合视点相关和视点无关的线绘制方法,提出一种基于GPU的实时绘制算法.基于视点曲率在图像空间中计算提取视点相关特征线,同时利用风格化纹理和主曲率信息绘制视点无关特征线.根据三维模型信息与预设计的风格化纹理,在像素着色器中对视点相关和视点无关的2类特征信息进行计算,然后结合两者结果得到令人满意的绘制结果.实验结果表明,由于所有计算在图像空间由GPU并行完成,可以高效地提取特征线;采用风格化纹理的设计增加了图像空间风格化绘制的可控性,弥补了图像空间算法的风格化可控性差的缺点.此外,文中算法不仅可以进行实时的风格化线绘制,以该算法为基础还可以进行进一步的艺术仿真,如国画的模拟等.     

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).