ClassificationIntroduction to Volume Rendering - Lichtenbelt, Crane, Naqvi
1. Classification is the property of assigning an opacity value to a voxel. This assignment is some property of the voxel, like it's intensity, or its local gradient magnitude. This function is called Opacity Transfer Function.
Opacity is a measure for how translucent that voxel is. It is a number between 0 and 1 that describes how much light that falls on a voxel will be absorbed by the voxel.
2. Shading is the process of mapping of the voxel intensity to an RGB color. It has 2 steps:-
i) Voxel intensities are converted into a color (process coloring)
ii)Shading model is applied to these colors
3. Coloring is the process of turning voxel intensities into colors
Once the transfer functions are set up, classification and coloring will be executed automatically and repeated for every rendering of the data.
Limitation: It is not possible to come up with transfer functions for each and every feature in a data set.
4. Segmentation is defined as a labeling of voxels indicating material types. It is not continuous like classification.
The labelling information can be stored with the data set and reused when necessary. Hence it is a pre-processing step, before the actual rendering is done.
Hence you can now make the classification and coloring transfer functions work on the labeling information.