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.     

基于输运方程的混合式体绘制模型

作者从物理光学中输运理论的输运方程出发，在散射项的计算上，提出了体散射强度和面散射强度的计算，以及用边界因子组合该两项射强度作为质点粒子在该点的总的散射光照强度的体绘制光照模型。     

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。     

使用VHD的可视人体成像方法研究

利用彩色数据进行体绘制，可以创建真实感图像，并具有揭示体内真实细节的能力。虽然彩色数据是可用的，但它并不包含依赖于视点的光线反射信息和光线在体素中的传播属性。本文提出了基于VHP彩色数据的体绘制算法框架，着重讨论了如何利用Phone光照模型进行着色，以及在HSI色彩空间中计算阻光度值。实验结果表明，本文算法成像质量高，可以表现人体的细微结构和纹理信息。     

一种用于半透明体绘制的光学模型

为了高效率地重建3维医学图像,并能充分显示内部隐含分界面及内部细节的详细信息,提出了一种能在普通硬件条件下实现的用于半透明体绘制的光学模型IVROM(improved volume rendering optical model)。该模型在光线吸收与发射模型的基础上,考虑了阴影、直接散射与间接散射等因素。此外,还详细介绍了结合该模型与Shear-Warp算法的半透明体绘制方法的实现。实验结果表明,采用该模型的半透明体绘制方法不仅效率高,而且显示效果好。     

An Extension of Fourier-Wavelet Volume Rendering by View Interpolation

This paper describes an extension to Fourier-wavelet volume rendering (FWVR), which is a Fourier domain implementation of the wavelet X-ray transform. This transform combines integration along the line of sight with a simultaneous 2-D wavelet transform in the view plane perpendicular to this line. During user interaction, only low resolution images are computed based on wavelet approximation coefficients. When user interaction ceases, the images are refined incrementally with the wavelet detail coefficients. The extension proposed in this paper is similar to a technique called view interpolation, which originates from the field of computer graphics. View interpolation is used to speed up rendering of complex scenes by precomputing images from a number of selected viewpoints. For intermediate viewpoints, rendering is performed by interpolating the precomputed images. In this paper, we show that for FWVR the speed of rendering low resolution images is increased by interpolation of precomputed sets of wavelet approximation coefficients in the Fourier domain. The differences with traditional view interpolation are that (i) interpolation is performed on the wavelet approximation coefficients in the Fourier domain and not on images, and (ii) interpolation is performed during user interaction only. When interaction ceases, ordinary FWVR progressively renders an image at high quality. Medical CT data are used to assess the accuracy and performance of the method. We use regular angular sampling of spherical coordinates which determine the viewing direction. The results show that angle increments as large as 10 degrees result in only a small degradation of image quality.     

多孔泡沫铝材料的体绘制与结构特征提取技术研究

利用Micro CT对泡沫铝材料重建后形成的体数据,运用体绘制的技术进行内部结构的显示,并对有效图像分割和体绘制加速等相关技术进行了研究.在此基础上,利用体绘制结果,运用八叉树算法,选取一定位置、范围的铝泡材料进行结构特征的分析和提取.结果表明,利用Micro CT和体绘制技术,可以显示来自于多孔材料的表面和内部的细节信息,对于结构特征信息的提取基本上和实测数据相符.     

Stochastic Volume Rendering of Multi‐Phase SPH Data

In this paper, we present a novel method for the direct volume rendering of large smoothed‐particle hydrodynamics (SPH) simulation data without transforming the unstructured data to an intermediate representation. By directly visualizing the unstructured particle data, we avoid long preprocessing times and large storage requirements. This enables the visualization of large, time‐dependent, and multivariate data both as a post‐process and in situ. To address the computational complexity, we introduce stochastic volume rendering that considers only a subset of particles at each step during ray marching. The sample probabilities for selecting this subset at each step are thereby determined both in a view‐dependent manner and based on the spatial complexity of the data. Our stochastic volume rendering enables us to scale continuously from a fast, interactive preview to a more accurate volume rendering at higher cost. Lastly, we discuss the visualization of free‐surface and multi‐phase flows by including a multi‐material model with volumetric and surface shading into the stochastic volume rendering.     

Progressive light volume for interactive volumetric illumination

We propose a technique named progressive light volume to support advanced volumetric illumination effects, such as single scattering and multi scattering. The light volume stores direct lighting information for sample points of the volume data. Using the light volume, we are able to compute the direct lighting for any point in the volume data with a single texture lookup. In order to keep the rendering at an interactive frame rate, we build the light volume progressively if necessary. During the light volume construction period, we use a fast ray casting algorithm to produce a rough rendering estimate from the light volume. After the light volume is built, we use a path tracer to continuously estimate the light intensity for each pixel. Our method puts no restrictions on the number, position, and type of lights. We conducted a comprehensive evaluation for various datasets. The rendering results show that our method is able to produce compelling images, and the performance results indicate that our method is practical for interactive use. Copyright © 2016 John Wiley & Sons, Ltd.     

一种等值面的折射体绘制方法

折射能增强体绘制图像的空间层次感和真实感。但是体数据中的噪声严重影响了绘制质量,而滤波又会造成绘制物体的几何变形和细节的损失。本文提出了一种等值面的折射体绘制方法。在绘制前,采用改进的基于曲率的PM滤波模型,用于噪声的平滑。在绘制时,通过设定阈值来消除等值面的重复折射现象。实验结果表明,本文方法采样点的错分率明显低于其他方法,绘制质量得到了显著的提高,同时几何变形和细节损失减少。     

基于小波的网络多分辨率体绘制

为了能在网络环境下，快速地进行三维绘制，提出了一种网络环境下的基于小波的体数据多分辨率体绘制方法，该方法采取基于客户端的三维重建方案，首先利用三维小波的多分辨率分析方法，将体数据分解为不同分辨率下的离散逼近信号与高频细节信号；然后按先离散逼近信号，后高频细节信号的次序将数据传输到客户端；最后在客户端实现由粗及精的、渐进式的三维绘制。在这个过程中，一种3D的Mallat滤波器组被用来加速体数据的3D小波分解与重构，一种离散的简略化小波域体绘制方程被用来满足体绘制的实时性。实验结果表明，由于该方法仅需要12．5％或更低的数据量，即可以绘制出品质良好的图像或图像的概貌，所以非常适宜于需要频繁选择、交互的三维图像网络系统。     

Shape-aware Volume Illustration

We introduce a novel volume illustration technique for regularly sampled volume datasets. The fundamental difference between previous volume illustration algorithms and ours is that our results are shape-aware, as they depend not only on the rendering styles, but also the shape styles. We propose a new data structure that is derived from the input volume and consists of a distance volume and a segmentation volume. The distance volume is used to reconstruct a continuous field around the object boundary, facilitating smooth illustrations of boundaries and silhouettes. The segmentation volume allows us to abstract or remove distracting details and noise, and apply different rendering styles to different objects and components. We also demonstrate how to modify the shape of illustrated objects using a new 2D curve analogy technique. This provides an interactive method for learning shape variations from 2D hand-painted illustrations by drawing several lines. Our experiments on several volume datasets demonstrate that the proposed approach can achieve visually appealing and shape-aware illustrations. The feedback from medical illustrators is quite encouraging.     

应用于传递函数设定的交互式体绘制工具

传递函数是体绘制过程中用以定出体数据与光学特征的对应关系,因此,传递函数的设定对成像质量有着直接的影响,文章提出一应用于传递函数设定、简单且有效的交互式体绘制工具,由于二维纹理硬件在通用的个人计算机上被普遍使用,因而该工具采用基于二维纹理硬件的体绘制方法,利用本工具,用户能根据体数据的直方图来交互地分别设定R、G、B和A四种传递函数,以定出体数据与光学特征的对应关系,并获得实时的反馈视觉信息(绘制结果),该工具亦提供一虚拟轨迹球让用户交互地改变观察体数据的视点,用户不但可以交互地控制放大或缩小比率来绘制体数据,还可以选择采用光照或由多重纹理实现的三线性插值来获得不同的绘制效果,该文描述开发此工具的各种技术,并给出利用此工具得到的一些绘制结果。     

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。     

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.     

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。     

Volume tracing of atmospheric environments

Current three-dimensional computer graphics assumes a vacuum space. The inclusion of atmosphere is essential for the modeling and rendering of natural phenomena. This paper presents a method of modeling atmospheric effects and rendering them using a volume tracing renderer. The model is built within a framework called the atmospheric cube. The atmospheric cube, or the A-cube, is a finite volume that encloses the three-dimensional scene to be modeled. The atmosphere is defined by particles of varying radii, which are distributed over the cube. The distribution of particles determines the density of atmosphere. The interaction of light with the atmosphere is divided into four cases to capture the characteristics of the atmospheric illumination by particles of different radii: absorption, Rayleigh scattering, Mie scattering, and geometric optics. The atmospheric equation is a combination of modeling techniques covering the four cases. To render the interaction of light with the atmosphere, we present the rendering technique called volume tracing. Examples of blue sky, sunset, hazy sky, shaft of light beam, and rainbow are given.     

体绘制中传递函数设计的研究现状与展望

在体绘制中,传递函数将3维数据场的采样点映射成光学参数,直接决定了绘制的效果,成为体绘制研究的关键。然而传递函数的设计存在盲目性、用户界面不直观、参数调节复杂等问题,针对这些问题,提出了许多解决方法。首先介绍传递函数的定义,总结各种设计传递函数的定义域、值域、映射规则的方法,然后从不同的角度对传递函数的设计方法作全面的概述,重点介绍图像中心法、数据中心法和对象中心法,既分析了这些方法的特点,又比较了它们之间的内在联系,并探讨了新的设计思路,展望了该领域未来的研究方向。     

Style Transfer Functions for Illustrative Volume Rendering

Illustrative volume visualization frequently employs non-photorealistic rendering techniques to enhance important features or to suppress unwanted details. However, it is difficult to integrate multiple non-photorealistic rendering approaches into a single framework due to great differences in the individual methods and their parameters. In this paper, we present the concept of style transfer functions. Our approach enables flexible data-driven illumination which goes beyond using the transfer function to just assign colors and opacities. An image-based lighting model uses sphere maps to represent non-photorealistic rendering styles. Style transfer functions allow us to combine a multitude of different shading styles in a single rendering. We extend this concept with a technique for curvature-controlled style contours and an illustrative transparency model. Our implementation of the presented methods allows interactive generation of high-quality volumetric illustrations.