Master's Thesis - Studierstube Augmented Reality Project - Graz ...

2.1 Technical Visualization
(a) One-dimensional transfer
function for mapping of data
values to opacity from section
4.4.1.1.
(b) Manipulating a threedimensional
transfer function
with control widgets as presented
by [Kniss2001]
(c) Segmented Volume data
rendered with style-transfer
functions as introduced by
[Bruckner2007]
Figure 2.7: Comparison of different direct volume rendering approaches using transfer
functions.
3D texture slicing Another technique is the well known rendering of 2D textures
intersecting a 3D volume texture. The main difference is that independent of the
number of measured slices, a constant number of planes are cut through a 3D texture
which contains the actual volumetric data. These slices are always directed towards the
viewer and perpendicular to the viewing direction. Rotation around this volume will
then only affect the mapping of these slices - with the constraints of aliasing artifacts -
whereas the 3D volume texture is placed fix. Consequently, different viewing directions
will result in different data mapped onto the 2D texture planes. Hence, a constant
transparency value of a slice or a special function related to them will then provide the
impression of a semi-transparent volume as shown with transfer function in paragraph
2.1.1.1. For example a constant transparency value
α =
1
num slices
for each slice - will result in the same as the projection of the averages from the
occurring values found on a ray starting from the eye point as described in the next paragraph.
Other transparency functions will allow arbitrary combinations of the evenly
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