一种基于时空一致性的视频抠取方法

提出了一种交互式的时空一致性视频抠取方法,能够有效地从视频序列中提取出移动的前景目标.只需在视频体上简单地勾画时空的前景和背景线条,然后构造一个拉普拉斯方程驱动线条在三维的视频体上进行扩散,得到一个粗糙的抠取结果.随后,采用一种新颖的保持时空一致性的抠取技术,利用局部的统计信息和邻域信息,通过少数的迭代即可收敛到全局最优的抠取结果.最后,最优化一个新的全局代价函数在整个三维体上重建前景颜色,如实地保留了抠图结果的时空连贯性.算法的每一步计算都可转化为线性方程组进行求解,因此对于千万像素级的视频数据,也能快速得到高质量的抠取结果.通过对复杂的视频序列进行测试,展示了高质量的抠图结果和算法的高效性.     

三维医学图像的体绘制技术综述

在分析三维医学图形体绘制技术的基础上,描述了射线投射法、足迹法、剪切-曲变法、基于硬件的3D纹理映射、频域体绘制法和基于小波的体绘制等典型算法,给出了各类算法的性能评价,展望了体绘制技术研究的发展前景。     

基于GPU图像直接体绘制算法分析与评价

近年来计算机图形硬件性能不断提高,利用硬件来实现体绘制过程中的某些环节以获取交互的绘制速率成为可能,是目前体绘制的研究热点。描述了基于GPU的光线投射法、2D纹理映射法和3D纹理映射法等典型算法,给出了各类算法的分析与性能评价,最后实现相关算法并得出实验结果。     

直接体绘制中交互显示控制技术研究

针对直接体绘制中的交互显示控制问题,在深入分析交互显示控制中的颜色控制、Alpha控制和区域控制方法的基础上,结合等值面提取与绘制方法的特点,提出了一种基于直方控制的类等值面交互显示控制方法,该方法通过用类似窄直方图的Alpha折线控制体数据的透明度从而实现类似等值面的显示。试验表明该方法不仅能够有效模拟等值面绘制效果,而且在等值面值变化时效率较等值面算法大大提高,能够有效满足实时性要求。     

直接体绘制技术研究

直接体绘制技术是可视化研究领域的一个重要分支,是目前最活跃的可视化技术之一。该文首先介绍了体绘制技术的原理,分析其实现的关键技术及算法。然后介绍了可视化工具VTK,及其对光线投射算法的实现过程。     

直接体绘制加速算法综述

针对当前体绘制存在的软件加速算法,将其分为空间剖分技术、光线相关、物空间相关和基于图像绘制技术等四类,分别介绍其算法基本内容.最后利用MIN-MAX八叉树加速算法设计一个直接体绘制系统.     

直接体绘制技术研究

直接体绘制技术是可视化研究领域的一个重要分支,是目前最活跃的可视化技术之一。该文首先介绍了体绘制技术的原理,分析其实现的关键技术及算法。然后介绍了可视化工具VTK,及其对光线投射算法的实现过程。     

基于体数据分类的直接体绘制传输函数研究

直接体绘制是形成于20世纪80年代后期的一个新研究领域,本论文提出了一种基于体数据的标量值和梯度的分类方法,采用该方法可获得体数据重要的信息,从而帮助研究人员准确地设置传输函数的不透明度和颜色参数,使绘制的图像更加清晰。     

直接体绘制技术在地质体三维可视化中的应用研究

将直接体绘制技术应用于地质体三维可视化,首先对原始钻孔数据进行插值、网格化等预处理得到满足直接体绘制需要的规则体数据,从而建立反映地层分布的地质体三维标量数据场;然后用直接体绘制技术绘制三维地质体,避免了体元建模方法中在对地质体进行剖切等操作时必须要解决的剖面与体元之间复杂的判断求交等过程。采用该方法实现了对某地区地质体的三维可视化。     

基于VTK的腹部医学图像体绘制应用研究

由于面绘制不能保留CT图像丰富的数据信息,无法良好地对于形状特征模糊的组织器官以及它们之间的层次关系进行三维显示,因此需要结合体绘制来为医生提供有力的病变分析依据。本文利用VTK开发包所提供的体绘制方法来实现腹部CT图像的三维重建,验证并比较了这几种方法各自的优缺点。实验结果表明,VTK用于CT图像的体绘制方法具有快速、效果好的特点,并可根据实际应用来选用不同的体绘制方法。     

Visibility-Aware Direct Volume Rendering

Direct volume rendering (DVR) is a powerful visualization technique which allows users to effectively explore and study volumetric datasets.Different transparency settings can be flexibly assigned to different structures such that some valuable information can be revealed in direct volume rendered images (DVRIs).However,end-users often feel that some risks are always associated with DVR because they do not know whether any important information is missing from the transparent regions of DVRIs.In this paper,we investigate how to semi-automatically generate a set of DVRIs and also an animation which can reveal information missed in the original DVRIs and meanwhile satisfy some image quality criteria such as coherence.A complete framework is developed to tackle various problems related to the generation and quality evaluation of visibility-aware DVRIs and animations.Our technique can reduce the risk of using direct volume rendering and thus boost the confidence of users in volume rendering systems.     

数字人切片数据的硬件加速体绘制

实现了一个PC平台下的体绘制硬件加速算法,并对中国数字人、美国可视化人数据集进行可视化．预处理去除图像背景时,将图像从RGB颜色空间转换到YCbCr颜色空间,然后对Cb分量进行Otsu阈值化处理,用生成的二值图像作为掩码图像去除背景．为支持任意大小的体数据,采取了分块策略,并使用BSP树组织数据块,以生成正确的绘制顺序．此外还设计了一种基于图像的CIELUV颜色空间L分量的梯度向量场的传输函数,并取得了良好的绘制效果．     

Composed Scattering Model for Direct Volume Rendering

Based on the equation of transfer in transport theory of optical physics,a new volume rendering model,called composed scattering model(CSM),is presented.In calculating the scattering term of the equation,it is decomposed into volume scattering intensity and surface scattering intensity,and they are composed with the boundary detection operator as the weight function.This proposed model differs from the most current volume rendering models in the aspect that in CSM segmentation and illumination intensity calculation are taken as two coherent parts while in existing models they are regarded as two separate ones.This model has been applied to the direct volume rendering of 3D data sets obtained by CT and MRI.The resultant images show not only rich details but also clear boundary surfaces.CSM is demonstrated to be an accurate volume rendering model suitable for CT and MRI data sets.     

Fast Visualization of Object Contours by Non-Photorealistic Volume Rendering

In this paper we present a fast visualization technique for volumetric data, which is based on a recent non-photorealistic rendering technique. Our new approach enables alternative insights into 3D data sets (compared to traditional approaches such as direct volume rendering or iso-surface rendering). Object contours, which usually are characterized by locally high gradient values, are visualized regardless of their density values. Cumbersome tuning of transfer functions, as usually needed for setting up DVR views is avoided. Instead, a small number of parameters is available to adjust the non-photorealistic display. Based on the magnitude of local gradient information as well as on the angle between viewing direction and gradient vector, data values are mapped to visual properties (color, opacity), which then are combined to form the rendered image (MIP is proposed as the default compositing stragtegy here). Due to the fast implementation of this alternative rendering approach, it is possible to interactively investigate the 3D data, and quickly learn about internal structures. Several further extensions of our new approach, such as level lines are also presented in this paper.     

基于PC图形硬件的直接体绘制技术综述

对基于PC图形硬件的直接体绘制技术进行了介绍、归类和总结，力求为本领域的的研究提供一个较为详实的背景资料。     

Depth of Field Effects for Interactive Direct Volume Rendering

In this paper, a method for interactive direct volume rendering is proposed for computing depth of field effects, which previously were shown to aid observers in depth and size perception of synthetically generated images. The presented technique extends those benefits to volume rendering visualizations of 3D scalar fields from CT/MRI scanners or numerical simulations. It is based on incremental filtering and as such does not depend on any pre‐computation, thus allowing interactive explorations of volumetric data sets via on‐the‐fly editing of the shading model parameters or (multi‐dimensional) transfer functions.