4.2 Overview

Volume rendering is one of the most popular algorithms for volume visualization. It is an image-based approach, i.e. a view and an image plane are set for which the projection of the volume is done pixel-by-pixel.
Volume rendering consists of two main parts. First, some pre-processing computations are done, to classify and shade each voxel of the volume : an opacity value is obtained for the classification and a colour value is obtained for the shading. Then, it is followed by the actual rendering part, i.e. the projection from three dimensional data to a two dimensional image.

The volume rendering pipeline is usually consists of :

• data preparation (pre-filtering, resampling, maybe segmentation)
• gradient computation
• classification by assigning opacity
• shading by assigning colour
• compositing and projection by ray casting