目标特征指导的多分辨率体绘制算法

多分辨率体绘制是解决海量数据体绘制的一种有效方法。但对于数据散乱分布、同质区域较小的体绘制数据（比如物探领域的地震信号数据）,传统的基于香农熵或均方差的多分辨率方式均难以有效实现降低数据量的效果。本文提出了一种基于目标特征的多分辨率体绘制方法。以数据体中的目标特征为指导,适当降低非目标区域的分辨率,在尽可能不丢失其目标区域信息的情况下,实现有效的多分辨率体绘制。本文方法能够在目标保证数据量的前提下,尽可能的通过丢弃非目标区域的信息量,进而保护数据体的关键信息,以得到较好的绘制效果。实验结果表明,本文方法能与传统方法相比能够更好的保证关键区域绘制效果,同时进一步的降低用于绘制的数据量。     

Interactive volume rendering of large fields

We first present the volume-rendering pipeline and the most typical of the existing methods for each pipeline stage. The complexity of each stage in terms of computing time is analyzed for each method. Then the demands and the scope of interactive volume rendering are briefly summarized. Based on this analysis we examine alternate solutions to optimize each pipeline stage in order to allow interactive visualization while maintaining the image quality. The proposed method maximizes interactive manipulation possibilities and minimizes runtimes by sampling at the Nyquist rate and by flexibly trading off quality for performance at any pipeline level. Our approach is suitable for rendering large, scalar, discrete volume fields such as semitransparent clouds (or X-rays) on the fly.     

Volumetric texture synthesis for non-photorealistic volume rendering of medical data

This paper presents a novel technique, called volumetric texture synthesis, for non-photorealistic volume rendering. It extends texture synthesis from 2D areas/3D surfaces to volumes. By selecting different texture samples, it allows for a wide variety of stylized rendering for the target volume. As a preprocessing step, volume data analysis is used to identify texture orientations for the volume. This is followed by volumetric texture synthesis, which generates 3D non-photorealistic textures along the identified texture orientations. Finally, standard volume rendering is applied to display the volume data decorated by the texture. Experimental results are provided in the paper.     

基于一种新模型的交互式体绘制算法的研究

交互式体绘制算法基于一个新的可视化模型。目的是研究一种快速预览技术，在可视化内部结构时不需要专门的耗时巨大的转换函数。用两个参数来控制一个非常简单的绘制模型。交互旋转技术不需要任何特殊的硬件支持，所以可以广泛应用在低配置的电脑上。     

基于图形硬件加速的体绘制关键技术综述

随着近年来计算机图形硬件性能的不断提高,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变为可能,并逐渐成为目前的研究热点。从体绘制的分类、明暗处理、重构、体积裁剪等4个角度对基于图形硬件加速的体绘制方法进行了分类综述,介绍了各种关键技术的研究进展和典型算法,并讨论了各自特点及其相互联系。     

基于打包索引纹理的大规模数据体绘制算法

针对大规模数据体绘制效率低下的问题,提出一种算法：对体数据进行纹理分块打包,移除空数据块,并创建数据块的索引数据,绘制时通过索引访问打包后的纹理实现大规模数据完全载入显存,同时在索引中标记空数据及高密度数据块的位置,绘制前生成其有效的立方体数据表达,结合早期光线终止与空域跳过等加速技术,有效地实现了大规模的体数据的实时绘制,同时保证了结果图像的质量。     

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.     

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。     

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.     

Improved perspective visibility ordering for object-order volume rendering

Finding a correct a priori back-to-front (BTF) visibility ordering for the perspective projection of the voxels of a rectangular volume poses interesting problems. The BTF ordering presented by Frieder et al. [6] and the permuted BTF presented by Westover [14] are correct for parallel projection but not for perspective projection [12]. Swan presented a constructive proof for the correctness of the perspective BTF (PBTF) ordering [12]. This was a significant improvement on the existing orderings. However, his proof assumes that voxel projections are not larger than a pixel, i.e. voxel projections do not overlap in screen space. Very often the voxel projections do overlap, e.g. with splatting algorithms. In these cases, the PBTF ordering results in highly visible and characteristic rendering artefacts. In this paper we analyse the PBTF and show why it yields these rendering artefacts. We then present an improved visibility ordering that remedies the artefacts. Our new ordering is as good as the PBTF, but it is also valid for cases where voxel projections are larger than a single pixel, i.e. when voxel projections overlap in screen space. We demonstrate why and how our ordering works at fundamental and implementation levels.     

Texture-based volume rendering of adaptive mesh refinement data

Many phenomena in nature and engineering happen simultaneously on rather diverse spatial and temporal scales. In other words, they exhibit a multi-scale character. A special numerical multilevel technique associated with a particular hierarchical data structure is adaptive mesh refinement (AMR). This scheme achieves locally very high spatial and temporal resolutions. Due to its popularity, many scientists are in need of interactive visualization tools for AMR data. In this article, we present a 3D texture-based volume-rendering algorithm for AMR data that directly utilizes the hierarchical structure. Thereby fast rendering performance is achieved even for high-resolution data sets. To avoid multiple rendering of regions that are covered by grids of different levels of resolution, we propose a space partitioning scheme to decompose the volume into axis-aligned regions of equal-sized cells. Furthermore the problems of interpolation artifacts, opacity corrections, and texture memory limitations are addressed. Published online: November 6, 2002 Correspondence to: R. K?hler     

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.     

Improving cache locality for GPU-based volume rendering

We present a cache-aware method for accelerating texture-based volume rendering on a graphics processing unit (GPU). Because a GPU has hierarchical architecture in terms of processing and memory units, cache optimization is important to maximize performance for memory-intensive applications. Our method localizes texture memory reference according to the location of the viewpoint and dynamically selects the width and height of thread blocks (TBs) so that each warp, which is a series of 32 threads processed simultaneously, can minimize memory access strides. We also incorporate transposed indexing of threads to perform TB-level cache optimization for specific viewpoints. Furthermore, we maximize TB size to exploit spatial locality with fewer resident TBs. For viewpoints with relatively large strides, we synchronize threads of the same TB at regular intervals to realize synchronous ray propagation. Experimental results indicate that our cache-aware method doubles the worst rendering performance compared to those provided by the CUDA and OpenCL software development kits.     

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.     

脑血管体绘制的快速表意式增强

利用3维可视化技术重构脑血管模型,获取脑血管及其相关组织的立体结构,对于辅助诊断脑血管疾病具有重要意义.鉴于脑血管位置的特殊性、形态的复杂性及灰度信息的多变性,要求重构技术能够清晰还原其空间结构.基于CUDA(computed unified device architecture)的光线投射体绘制,引入深度和轮廓宽度等因子,采用基于曲率的轮廓增强、基于深度的边界增强以及基于立体显示和颜色融合的深度线索提示等表意式技术,实时重构高质量3维血管模型,生动展现脑血管的3维结构信息,如深度、梯度、观察方向等.实验结果表明,本文方法的有效性,在精确显示脑血管结构的同时能够增强体绘制效果.     

A selective rendering method for data visualization

Selective visualization is a solution for visualizing data of large size and dimensionality. In this paper a new method is proposed for effectively rendering certain chosen parts among the full set of data in terms of a colour buffer, referred to as the virtual plane, for storing intermediate results. By this method, scientists may concentrate their attention on the contents of data in which they are interested. Besides, the method could be easily integrated with all the current direct volume rendering techniques, especially progressive refinement methods and selective methods. Copyright © 1999 John Wiley & Sons, Ltd.     

A heterogeneous computing system for coupling 3D endomicroscopy with volume rendering in real-time image visualization

Modern microscopic volumetric imaging processes lack capturing flexibility and are inconvenient to operate. Additionally, the quality of acquired data could not be assessed immediately during imaging due to the lack of a coherent real-time visualization system. Thus, to eliminate the requisition of close user supervision while providing real-time 3D visualization alongside imaging, we propose and describe an innovative approach to integrate imaging and visualization into a single pipeline called an online incrementally accumulated rendering system. This system is composed of an electronic controller for progressive acquisition, a memory allocator for memory isolation, an efficient memory organization scheme, a compositing scheme to render accumulated datasets, and accumulative frame buffers for displaying non-conflicting outputs. We implement this design using a laser scanning confocal endomicroscope, interfaced with an FPGA prototyping board through a custom hardware circuit. Empirical results from practical implementations deployed in a cancer research center are presented in this paper.     

面向大规模地震体的多切片实时交互绘制优化

在普通计算平台上实现大规模地震体的多切片可视化时,传统缓存调度方法由于未考虑体块与切片的空间关联,导致交互时体块命中率较低,而常用的多分辨率绘制方法也难以达到较高的绘制质量,针对这些问题,设计了一种新的高速缓存调度策略——最大距离先出（MDFO）。首先,根据交互切片的空间位置改进缓存中体块的调度优先级,保证候选体块在切片连续交互时有更高的命中率;然后,提出了两阶段切片交互绘制方法,通过使用固定分辨率体块保证交互的实时性,通过渐进细化提升最终显示质量,并进一步结合体块数据的信息熵提升用户感兴趣区域的分辨率。实验结果表明,所提方法能够有效提高体块的整体命中率,提升比例达到60%以上,同时也实现了面向应用需求的高质量图像显示,较好地解决了大规模地震体可视化在交互效率与显示质量间的矛盾。     

An Efficient 2½ D rendering and Compositing System

We describe a method for doing image compositing using either 2D geometric shapes or raster images as input primitives. The resolution of the final image is virtually unlimited but, as no frame buffer is used, performance is much less dependant on resolution than with standard painting programs, allowing rendering very large images in reasonable time. Many standard features found in compositing programs have been implemented, like hierarchical data structures for input primitives, lighting control for each layer and filter operations (for antialiasing or defocus).     

GPU加速的八叉树体绘制算法

提出一种针对物体空间为序体绘制的空域跳过算法：采用双层次空间跳过,先以规则的数据分块作粗略地跳过,再以八叉树获得更高粒度的优化。该方法进一步解决了超过可用纹理内存容量的大规模体数据实时绘制问题,允许实时改变传递函数。针对该算法引入的CPU高负载瓶颈,提出一种新算法,在图形处理器(GPU)内快速计算采样面片,平衡了CPU与GPU间的运算负载。结合上述两种算法,实现高效的大规模体数据绘制并无损图像质量。