一个新的体绘制加速算法

针对目前加速方式与传递函数交互设定需求的矛盾,提出了一个新的基于边缘切除原理的体绘制加速算法。算法针对两个关键难点:如何消除传递函数调整依赖性,如何识别空体素,提出了有效的绝对空体素识别准则,设计了高效的边缘空体素分离机制,构成了不依赖传递函数调整的加速模式。在保持高的图像质量的前提下,边缘切除算法具有显著的绘制速度提升。边缘切除过程在预处理阶段进行,算法参数易于选取和推广,具有广泛的适应性,非常适合需要交互设定传递函数的普及型医学图像分析系统应用。算法采用了规则的边缘切除方式,收缩后的体数据非常方便后续光线投射或溅射算法应用,可以方便地与其他各种加速方式组合使用,使不同角度的加速效果实现叠加,是当前各种主流加速技术的一个很好的互补技术。不同背景的运算实例,测试和验证了算法的有效性。     

基于空间数据插值算法的空间散乱数据体绘制实现

体绘制技术是一种能够真实地反映空间数据场内部信息的可视化技术。在体绘制研究领域中,非规则的空间散乱数据体绘制目前仍然是一个研究热点。文中采用空间数据插值算法对散乱的原始数据进行网格化插值,然后使用光投影体绘制算法对规则网格数据进行体绘制。最后,通过新方法实现了某油藏区地下流体压力和孔隙度分布结构的体绘制。     

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。     

Real-time ray casting rendering of volume clipping in medical visualization

This paper presents a real-time ray casting rendering algorithm for “volume clipping plane“ as an extension of the conventional ray casting technique.For each viewing direction a(moderate) pre-processing step is performed:the ray traverses the entire volume data (no early ray termination).Its intensity and opacity contributions are divided into several segments which are then sorted and stored by depth.At each sampling position along a segment,accumulated trans-parency and color are stored at a moderate memory overhead.For visualizing real-time volumeclipping,only relevant segment contributions (maximum two) at the location of the clipping plane are considered,thus reducing the calculation to meet real-time requirements.Compared with theprevious work that involves time-consuming re-clipping,re-traversing and re-shading,the proposed method achieves quality identical to ray casting at real-time speed.The performance is indepen-dent of the volume resolution and/or the number of clipping planes along a given viewing direction.Therefore it is suitable for real-time “internal volume inspections“,involving one or several cutting planes,typically applied e.g.,in medical visualization and material testing applications.     

Direct volume rendering of multiple scalar fields

Rendering of volume data without forming geometric objects is often termed direct volume rendering. Most of the previously developed methods for this purpose are restricted to display of one scalar variable. This paper presents methods for direct volume rendering of several scalar variables defined at discrete points in three-dimensional space. Typical requirements for the rendering of such data are proposed and then used as a basis for the derivation of a computational model. The proposed model uses a classification technique to composite specific types of information from different scalar fields. The visual display of the composite information is controlled through a set of rendering parameters.     

工业CT数据场面绘制和体绘制改进算法研究

工业CT图像的重建速度和精度是工业CT产品的两个重要指标。针对面绘制的MC算法提出了一种基于相似性区域分割的三维工业图像表面重建算法,实现了准确分割,并利用分割结果精确地提取等值面,显著提高了检测效率;针对体绘制的光线投射算法提出了一种基于二维最大熵阈值的分割预处理方法,利用二维直方图熵最大化寻找阈值的最佳组合,能有效减少重建体数据量,实测数据表明体绘制速度明显提高。     

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.     

基于体元投影的一种非规则数据场体绘制方法

随着科学计算可视化的发展及其在实践中的应用,非规则数据场的可视化已成为当前的研究热点之一。由于非规则场中样点的大小、形状和分布是不一致的,在成像时面临更多的困难。常用的方法有光线投射法,单元投影法,以及单元投影与光线投射相结合等算法。吸取了上述算法的优点,同时利用非规则数据场的一些特性,采用了一些加速措施来加速绘制。通过实验验证,可以达到比较理想的效果。     

基于快速求交的自适应光线投射法

光线投射是一个重要的体绘制算法,但直线上采样点的确定是非常费时的,也是影响体绘制实时性的重要因素。该文利用直线和平面族的交点可以快速求得直线上的采样点及其特征值,该方法充分利用了直线的相关性,避免了大量的三线性插值计算。该文还基于快速求交提出了自适应采用方法,以提高绘制图像的质量。     

Object‐order template‐based approach for stereoscopic volume rendering

Stereoscopic volume rendering provides powerful depth information, but it takes a long time to render two‐eye images. Previous algorithms based on reprojection methods project the result of one view of a stereo pair into the other instead of rendering a new one completely. Because of inaccurate mapping between the two images, the quality of the reprojected image is not satisfactory. This paper presents a new algorithm to preserve the accuracy of both images with very little increase in computation time. The efficiency of the new algorithm comes from the use of ray templates and object‐order processing. This algorithm makes two different templates for each eye and renders two images simultaneously, tracing the volume only once in object order. We also extend the algorithm to support image‐space supersampling by using more ray templates. Experimental results show that the image quality of the new algorithm is not only comparable with that of ray casting but also the rendering speed is near that of the interactive shear–warp algorithm employing object‐order processing and spatial data coherency. Copyright © 1999 John Wiley & Sons, Ltd.     

基于最优化分块的大规模数据体绘制加速方法

GPU加速体绘制已成为体可视化领域的研究热点,然而超出显存的大规模数据无法直接载入,成为GPU应用的瓶颈。分块技术能够在保证图像质量的条件下解决该问题,但分块数据的频繁加载和访问明显降低了绘制速度。针对上述问题,通过建立最优化分块模型得到了大规模数据的最优分块,并通过构造节点编号纹理和改进距离模板设计的方法进一步提高了基于八叉树的分块体绘制算法的绘制速度。实验结果表明,该方法加速效果明显。     

MaterialVis: Material visualization tool using direct volume and surface rendering techniques

Visualization of the materials is an indispensable part of their structural analysis. We developed a visualization tool for amorphous as well as crystalline structures, called MaterialVis. Unlike the existing tools, MaterialVis represents material structures as a volume and a surface manifold, in addition to plain atomic coordinates. Both amorphous and crystalline structures exhibit topological features as well as various defects. MaterialVis provides a wide range of functionality to visualize such topological structures and crystal defects interactively. Direct volume rendering techniques are used to visualize the volumetric features of materials, such as crystal defects, which are responsible for the distinct fingerprints of a specific sample. In addition, the tool provides surface visualization to extract hidden topological features within the material. Together with the rich set of parameters and options to control the visualization, MaterialVis allows users to visualize various aspects of materials very efficiently as generated by modern analytical techniques such as the Atom Probe Tomography.     

基于GPU Raycasting算法的矢量/栅格混合绘制研究*

Raycasting体绘制算法由于成像质量高而被广泛应用于体数据的可视化,但当线、面表达的矢量数据和三维栅格表达的体数据同时绘制到同一场景时,由于绘制方法的差异会造成矢量和栅格数据空间遮挡关系不一致。在GPU实现Raycasting算法的基础上,通过矢量和栅格数据先后绘制,采用FBO离屏绘制等技术将矢量数据绘制到深度缓存纹理并在体绘制采样和融合中统一考虑矢栅颜色融合。实验结果表明,该算法在矢量数据非透明模式下能正确处理矢量栅格数据的混合绘制。     

基于图形处理器加速光线投射算法的多功能体绘制技术

为克服传统算法中体绘制交互速度不流畅、重建耗时长、绘制效果单一的不足,实现了基于图形处理器(GPU)的光线投射算法用于医学层析图像实时体绘制,并能快速切换不同组织器官的绘制效果。首先,读入医学层析图像到计算机内存,构造体素;然后,设置相应体素属性(如插值方式、着色处理、光照参数)等,设计显示不同组织器官的颜色及不透明度传输函数;最后,GPU加载体素据并进行光线投射算法的计算。实验结果表明,在绘制速度上,GPU加速光线投射算法实现的多功能体绘制技术的绘制速度能达到每秒40帧以上,完全满足临床应用需求。在绘制质量上,用户交互中由于重采样而产生的锯齿现象明显低于CPU端实现的光线投射算法,GPU端与CPU端绘制时间的加速比在9倍左右。     

Application paper. Applying ray casting to the flow visualization data using linear and B-spline hyperpatch interpolation

Visualizing the flow of air or fluids is especially challenging because of their transparency and possible high velocity. Complex patterns are created when the flow is over or around an object. Our aim is to visualize the flow in three dimensions, eliminating the need for mentally piecing the flow from two-dimensional slices. We have applied the well-known ray casting technique to visualize the flow around an aircraft wing. During ray casting, when the ray does not intercept the lattice points, linear and B-spline hyperpatch interpolations are used to estimate the colour. We describe the shading equation, and compare the linear and the B-spline hyperpatch interpolation schemes during ray casting. Several images are produced to show the difference in the image quality of these two methods, and their image generation time.     

基于GPU与Monte-Carlo的体绘制光线投射算法的研究

体绘制过程中等距离采样在显示效果不理想的情况下,每减少一个采样步长会增加大量采样点,大大增加了体绘制过程中的计算负担。针对这个问题,提出了一种基于Monte-Carlo积分方法的光线投射实现的实时体绘制算法,采用Monte-Carlo积分方法解决了光照明方程中的积分问题。实验结果表明,在显示效果几乎一样的前提下,采用本文的方法绘制效率提高了十多帧。     

A framework for fusion methods and rendering techniques of multimodal volume data

Many different direct volume rendering methods have been developed to visualize 3D scalar fields on uniform rectilinear grids. However, little work has been done on rendering simultaneously various properties of the same 3D region measured with different registration devices or at different instants of time. The demand for this type of visualization is rapidly increasing in scientific applications such as medicine in which the visual integration of multiple modalities allows a better comprehension of the anatomy and a perception of its relationships with activity. This paper presents different strategies of direct multimodal volume rendering (DMVR). It is restricted to voxel models with a known 3D rigid alignment transformation. The paper evaluates at which steps of the rendering pipeline the data fusion must be realized in order to accomplish the desired visual integration and to provide fast re‐renders when some fusion parameters are modified. In addition, it analyses how existing monomodal visualization algorithms can be extended to multiple datasets and it compares their efficiency and their computational cost. Copyright © 2004 John Wiley & Sons, Ltd.     

基于PC的医学图像体绘制方法研究与仿真

体绘制技术是一种能够准确反映体数据内部信息的可视化技术。本文主要介绍了一种改进的体绘制算法，即首先对三维医学图像施加模糊增强，然后对增强后的图像进行模糊阈值分割，从而可以清晰地对三维数据场进行分类，即边界区与非边界区。对边界区与非边界区分别进行绘制。在PC机上进行仿真的结果表明，此方法既能提高绘制的速度，又能保证绘制质量。     

Using 2- and 2 -dimensional seed filling in view lattice to accelerate volumetric rendering

In this paper we propose new methods for calculating the projection of an opaque 3-dimensional 6-connected volumetric object into a two-dimensional view using 2- and 2 -dimensional seed-filling in the view space. When a 3-dimensional volumetric data set is sampled by parallel rays at a resolution exceeding the Nyquist ratio, the 6-connectivity of objects is maintained from volume lattice to view lattice. Given a seed point for each 6-connected object in the volumetric data set, a seed-filling algorithm may access all sample points in view lattice, while simultaneously composing the rendered view. The algorithms presented in this paper minimize the number of voxels that need to be processed. We implemented these methods on a general purpose computer architecture and tested them with several artificial and real-life medical volumetric data sets. It is shown that the algorithms may be used to speed up the parallel ray casting of opaque medical objects. The actual frame rate achieved by the combined method allows interactive (10 frames/sec) rotation of the object on a common single-processor personal computer without specialized hardware.     

大规模数据快速体绘制方法的设计与实现

体绘制是科学计算可视化的重要手段,针对大规模数据场体绘制计算量大、效率低的问题,提出一种基于哈尔小波变换的三维规则网格数据场快速体绘制方法.采用整体描述、局部细化的策略对转换后的数据进行组织、管理和调度,实现了多尺度分析和快速随机存取,并有效解决了CPU在处理大规模数据集时纹理内存的局限;采用基于CUDA(计算统一设备架构)的GPU加速技术提高体绘制算法性能,很好的实现了大规模数据集的交互式可视化.