面向体绘制图像的直接体对象抠取

针对三维体对象抠取的相关工作中存在的尚多不足,提出一种体对象抠取算法.首先计算出与用户勾画结果相关的三维数据点,然后基于K-means聚类方法标记出高置信度的属于目标对象和无关对象的三维数据点,并以此作为种子点,借助基于能量优化的图割算法最终得到正确的体对象抠取结果.用户只需直接在体绘制的二维颜色叠加结果上通过简单的勾画指定目标对象和无关对象,即可抠取出感兴趣的体结构.最后通过实验说明了该算法的有效性.     

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。     

A Multidirectional Occlusion Shading Model for Direct Volume Rendering

In this paper, we present a novel technique which simulates directional light scattering for more realistic interactive visualization of volume data. Our method extends the recent directional occlusion shading model by enabling light source positioning with practically no performance penalty. Light transport is approximated using a tilted cone‐shaped function which leaves elliptic footprints in the opacity buffer during slice‐based volume rendering. We perform an incremental blurring operation on the opacity buffer for each slice in front‐to‐back order. This buffer is then used to define the degree of occlusion for the subsequent slice. Our method is capable of generating high‐quality soft shadowing effects, allows interactive modification of all illumination and rendering parameters, and requires no pre‐computation.     

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.     

彩色三维体数据场的直接体绘制方法

提出基于光线投射和三维纹理映射的彩色体数据成像算法，研究如何从每个体素的R，G，B三元组映射成不透明度值，即不透明度转换函数。首先把原始的RGB色彩空间转换成LUV色彩空间；然后以亮度分量的中心差分来近似估计法向量，并应用Phong光照模型进行着色，根据亮度分量及其梯度等信息计算不透明度值；最后合成、累积颜色。对美国数字人男子照相彩色体数据分别采用两种算法进行实验。结果表明：基于光线投射的彩色体数据算法成像质量较高，可以表现体表毛细血管等细微结构，但速度较慢；基于三维纹理映射的彩色体数据成像算法速度较快，但成像质量适中。     

A Directional Occlusion Shading Model for Interactive Direct Volume Rendering

Volumetric rendering is widely used to examine 3D scalar fields from CT/MRI scanners and numerical simulation datasets. One key aspect of volumetric rendering is the ability to provide perceptual cues to aid in understanding structure contained in the data. While shading models that reproduce natural lighting conditions have been shown to better convey depth information and spatial relationships, they traditionally require considerable (pre)computation. In this paper, a shading model for interactive direct volume rendering is proposed that provides perceptual cues similar to those of ambient occlusion, for both solid and transparent surface-like features. An image space occlusion factor is derived from the radiative transport equation based on a specialized phase function. The method does not rely on any precomputation and thus allows for interactive explorations of volumetric data sets via on-the-fly editing of the shading model parameters or (multi-dimensional) transfer functions while modifications to the volume via clipping planes are incorporated into the resulting occlusion-based shading.     

面向医学数据的分层剥离体绘制算法

采用直接体绘制方法显示医学数据时,一般通过修改传递函数来显示感兴趣区域,但仅通过调节传递函数很难清晰地显示被遮挡的人体组织,为此提出一种新的分层剥离直接体绘制算法.通过计算相邻的不透明度极小值和极大值之间的斜率,并根据用户指定的斜率阈值和累积不透明度阈值确定分层点,实现对体数据的分层绘制.实验结果证明,该算法可以根据不同医学数据的特征信息更精确地定位分层点,绘制效果清晰,速度较快.     

Hypergraph-Partitioning-Based Remapping Models for Image-Space-Parallel Direct Volume Rendering of Unstructured Grids

In this work, image-space-parallel direct volume rendering (DVR) of unstructured grids is investigated for distributed-memory architectures. A hypergraph-partitioning-based model is proposed for the adaptive screen partitioning problem in this context. The proposed model aims to balance the rendering loads of processors while trying to minimize the amount of data replication. In the parallel DVR framework we adopted, each data primitive is statically owned by its home processor, which is responsible from replicating its primitives on other processors. Two appropriate remapping models are proposed by enhancing the above model for use within this framework. These two remapping models aim to minimize the total volume of communication in data replication while balancing the rendering loads of processors. Based on the proposed models, a parallel DVR algorithm is developed. The experiments conducted on a PC cluster show that the proposed remapping models achieve better speedup values compared to the remapping models previously suggested for image-space-parallel DVR     

State of the Art in Transfer Functions for Direct Volume Rendering

A central topic in scientific visualization is the transfer function (TF) for volume rendering. The TF serves a fundamental role in translating scalar and multivariate data into color and opacity to express and reveal the relevant features present in the data studied. Beyond this core functionality, TFs also serve as a tool for encoding and utilizing domain knowledge and as an expression for visual design of material appearances. TFs also enable interactive volumetric exploration of complex data. The purpose of this state‐of‐the‐art report (STAR) is to provide an overview of research into the various aspects of TFs, which lead to interpretation of the underlying data through the use of meaningful visual representations. The STAR classifies TF research into the following aspects: dimensionality, derived attributes, aggregated attributes, rendering aspects, automation, and user interfaces. The STAR concludes with some interesting research challenges that form the basis of an agenda for the development of next generation TF tools and methodologies.     

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。     

GPU Accelerated Direct Volume Rendering on an Interactive Light Field Display

We present a GPU accelerated volume ray casting system interactively driving a multi‐user light field display. The display, driven by a single programmable GPU, is based on a specially arranged array of projectors and a holographic screen and provides full horizontal parallax. The characteristics of the display are exploited to develop a specialized volume rendering technique able to provide multiple freely moving naked‐eye viewers the illusion of seeing and manipulating virtual volumetric objects floating in the display workspace. In our approach, a GPU ray‐caster follows rays generated by a multiple‐center‐of‐projection technique while sampling pre‐filtered versions of the dataset at resolutions that match the varying spatial accuracy of the display. The method achieves interactive performance and provides rapid visual understanding of complex volumetric data sets even when using depth oblivious compositing techniques.     

Compressive Volume Rendering

Compressive rendering refers to the process of reconstructing a full image from a small subset of the rendered pixels, thereby expediting the rendering task. In this paper, we empirically investigate three image order techniques for compressive rendering that are suitable for direct volume rendering. The first technique is based on the theory of compressed sensing and leverages the sparsity of the image gradient in the Fourier domain. The latter techniques exploit smoothness properties of the rendered image; the second technique recovers the missing pixels via a total variation minimization procedure while the third technique incorporates a smoothness prior in a variational reconstruction framework employing interpolating cubic B‐splines. We compare and contrast the three techniques in terms of quality, efficiency and sensitivity to the distribution of pixels. Our results show that smoothness‐based techniques significantly outperform techniques that are based on compressed sensing and are also robust in the presence of highly incomplete information. We achieve high quality recovery with as little as 20% of the pixels distributed uniformly in screen space.     

体绘制技术

可视化技术是继计算、实验两大科学研究方法之后的第三种研究方法,体绘制技术作为可视化技术的一个重要分支,已经取得长足发展。对常用体绘制技术进行了分类,并且指出、分析了各自特点及适用场合,为进一步应用、改进这些技术提供参考。     

加速体绘制技术

根据体绘制成像的各个操作环节，对体绘制的加速技术进行了较全面且系统的介绍，包括色彩合成、光线与数据的求交、插值计算、排序及视见变换、对体绘制的基于硬件及系统方面的加速技术（如并行体绘制和漫游体绘制）也进行了一些讨论，在实际应用中，只有将各种加速技术进行有机地结合才能充分发挥体绘制的可视化作用。     

Parallel Irradiance Caching for Interactive Monte‐Carlo Direct Volume Rendering

We propose a technique to build the irradiance cache for isotropic scattering simultaneously with Monte Carlo progressive direct volume rendering on a single GPU, which allows us to achieve up to four times increased convergence rate for complex scenes with arbitrary sources of light. We use three procedures that run concurrently on a single GPU. The first is the main rendering procedure. The second procedure computes new cache entries, and the third one corrects the errors that may arise after creation of new cache entries. We propose two distinct approaches to allow massive parallelism of cache entry creation. In addition, we show a novel extrapolation approach which outputs high quality irradiance approximations and a suitable prioritization scheme to increase the convergence rate by dedicating more computational power to more complex rendering areas.     

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。