ABSTRACT
The process of creating an image from the data, as the last step before display, in the visualization pipeline is called rendering; this is a key aspect of all high performance visualizations. As shown in Figure 1.1, the rendering process takes data resulting from visualization algorithms and generates an image for display. This figure highlights that data is typically filtered, transformed, subsetted and then mapped to renderable geometry before rendering takes place. There are two forms of rendering typically used in visualization, based
generated sualization mapping algorithms (see Fig. 1.1) and direct rendering from the data. For geometric rendering, typical high performance visualization packages use the OpenGL library, which converts the geometry generated by visualization mapping algorithms to colored pixels through rasterization [36]. Another method for generating images from geometry is ray tracing, where rays from the viewpoint through the image pixels, are intersected with geometry to form the colored pixels [35]. Direct rendering does not require an intermediate mapping of data to geometry, but rather, it directly generates the colored pixels through a mapping that involves sampling the data and for each sample, mapping the data to renderable quantities (color and transparency). Direct volume rendering is a common technique for rendering scalar fields directly into images.
