The goal of the transfer function in visualization applications is to emphasize or classify features of interest in the data. Optical parameters are specified by the data values directly, or they are computed from applying one or more transfer functions to the data. More complex models incorporate local illumination and volumetric shadows, and they account for light scattering effects. For example, the most commonly used model assumes that the volume consists of particles that simultaneously emit and absorb light. In essence, the role of the optical model is to describe how particles in the volume interact with light.
This process is known as reconstruction and plays an important role in volume rendering and processing applications. Values at intermediate locations are obtained by interpolating data at neighboring volume elements. The term voxel denotes an individual "volume element," similar to the terms pixel for "picture element" and texel for "texture element." Each voxel corresponds to a location in data space and has one or more data values associated with it. In graphics memory, volume data is stored as a stack of 2D texture slices or as a single 3D texture object. During rendering, optical properties are accumulated along each viewing ray to form an image of the data (see Figure 39-2).įigure 39-2 The Process of Volume RenderingĪlthough the data set is interpreted as a continuous function in space, for practical purposes it is represented by a uniform 3D array of samples. These techniques use an optical model to map data values to optical properties, such as color and opacity (Max 1995). 39.2 Volume Renderingĭirect volume rendering methods generate images of a 3D volumetric data set without explicitly extracting geometric surfaces from the data (Levoy 1988). Section 39.6 concludes with a summary of relevant performance considerations. Section 39.5 describes advanced techniques for incorporating more realistic lighting effects and adding procedural details to the rendering. Section 39.4 provides additional implementation details, which expand the capabilities of the basic volume renderer. Section 39.3 describes the components of a typical texture-based volume rendering application, and illustrates it with a simple example. Section 39.2 introduces the terminology and explains the process of direct volume rendering. Texture-based techniques are easily combined with polygonal algorithms, require only a few render passes, and offer a great level of interactivity without sacrificing the quality of rendering. 2003, Krüger and Westermann 2003), this chapter describes texture-based volume rendering only. Although it is possible to implement other popular volume rendering algorithms on the GPU, such as ray casting (Roettger et al. This chapter describes volume rendering techniques that exploit the flexible programming model and 3D texturing capabilities of modern GPUs. Users of interactive volume rendering applications rely on the performance of modern graphics accelerators for efficient data exploration and feature discovery. Examples include visualization of data acquired by medical imaging devices or resulting from computational fluid dynamics simulations. In addition to modeling and rendering volumetric phenomena, volume rendering is essential to scientific and engineering applications that require visualization of three-dimensional data sets. These models assume that light is emitted, absorbed, and scattered by a large number of particles in the volume. Volumetric models are better suited for creating such effects. Fluids, clouds, fire, smoke, fog, and dust are difficult to model with geometric primitives. Many visual effects are volumetric in nature. This chapter presents texture-based volume rendering techniques that are used for visualizing three-dimensional data sets and for creating high-quality special effects. The CD content, including demos and content, is available on the web and for download. You can purchase a beautifully printed version of this book, and others in the series, at a 30% discount courtesy of InformIT and Addison-Wesley. GPU Gems GPU Gems is now available, right here, online.
0 kommentar(er)
