Overview of Volume Rendering

Volume visualization is a method of extracting meaningful information from volumetric data using interactive graphics and imaging. It is concerned with volume data representation, modeling, manipulation, and rendering [31][100][101][176]. Volume data are 3D (possibly time-varying) entities that may have information inside them, might not consist of tangible surfaces and edges, or might be too voluminous to be represented geometrically. They are obtained by sampling, simulation, or modeling techniques. For example, a sequence of 2D slices obtained from Magnetic Resonance Imaging (MRI), Computed Tomography (CT), functional MRI (fMRI), or Positron Emission Tomography (PET), is 3D reconstructed into a volume model and visualized for diagnostic purposes or for planning of treatment or surgery. The same technology is often used with industrial CT for non-destructive inspection of composite materials or mechanical parts. Similarly, confocal microscopes produce data which is visualized to study the morphology of biological structures. In many computational fields, such as in computational fluid dynamics, the results of simulations typically running on a supercomputer are often visualized as volume data for analysis and verification. Recently, the area of volume graphics [104] has been expanding, and many traditional geometric computer graphics applications, such as CAD and flight simulation, have been exploiting the advantages of volume techniques. Over the years many techniques have been developed to render volumetric data. Since methods for displaying geometric primitives were already well-established, most of the early methods involve approximating a surface contained within the data using geometric primitives. When volumetric data are visualized using a surface rendering technique, a dimension of information is essentially lost. In response to this, volume rendering techniques were developed that attempt to capture the entire 3D data in a single 2D image. Volume rendering convey more information than surface rendering images, but at the cost of increased algorithm complexity, and consequently increased rendering times. To improve interactivity in volume rendering, many optimization methods both for software and for graphics accelerator implementations, as well as several special-purpose volume rendering machines, have been developed.