1. Pre-Integrated Volume Rendering: Past, Present, Future
Martin Kraus
December 16, 2004

2. Contents
past:
publications summarized in the chapter “Pre-Integrated Volume Rendering” of “The Visualization Handbook.”
present:
new publications in 2004
future:
open problems/work in progress
Pre-Integrate Volume Rendering: Past, Present, Future

3. Pre-Integration: The Past
reference: Kraus and Ertl, “Pre-Integrated Volume Rendering” in Johnson and Hansen (eds.), “The Visualization Handbook”, 2004
written: Spring 2003
goals:
structured summary of pre-integrated techniques
consistent notation
show the big picture
Pre-Integrate Volume Rendering: Past, Present, Future

4. Pre-Integration: The Past
contents of chapter 10 in the Vis Handbook:
introduction to pre-int. volume rendering
pre-integrated volume rendering algorithms
accelerated pre-integration
pre-integrated rendering techniques
open problems
Pre-Integrate Volume Rendering: Past, Present, Future

5. Pre-Integration: The Past
introduction to pre-int. volume rendering
volume rendering integral
pre- and post- classification
numerical integration
pre-integrated classification
viewing
ray
pixel
sampling
points
eye point
viewing ray
back
front
sampling
sampling
point
eye point
point
Pre-Integrate Volume Rendering: Past, Present, Future

6. Pre-Integration: The Past
pre-integrated volume rendering algorithms
pre-integrated cell projection
Max et al (VolVis)
Röttger et al (Vis), 2002 (VolVis)
Guthe et al (HWWS)
Weiler et al (VolVis), 2003 (TVCG)
pre-int. texture-based volume rendering
Engel et al (HWWS)
...
Pre-Integrate Volume Rendering: Past, Present, Future

7. Pre-Integration: The Past
pre-integrated volume rendering algorithms
...
pre-integrated ray casting
Knittel 2002 (EG)
Meißner et al (HWWS)
Roettger et al (VisSym)
Weiler et al (Vis)
pre-integrated shear-warp algorithm
Schulze et al (VG)
Pre-Integrate Volume Rendering: Past, Present, Future

8. Pre-Integration: The Past
accelerated pre-integration
local updates of lookup tables
particular optical models
pre-int. for a single sampling distance
pre-int. without self-attenuation of segments
hardware-accelerated pre-integration
Roettger et al (VolVis)
incremental pre-integration
Weiler et al (Vis)
Pre-Integrate Volume Rendering: Past, Present, Future

9. Pre-Integration: The Past
pre-integrated rendering techniques
isosurface rendering
Röttger et al (Vis)
Engel et al (HWWS)
volume shading
Meißner et al (GI)
volume clipping
Roettger et al (VisSym)
Pre-Integrate Volume Rendering: Past, Present, Future

10. Pre-Integration: The Past
open problems
multidimensional transfer functions
see also Kniss et al (Vis)
other volume rendering algorithms
additional acceleration techniques
further illumination models
higher-order interpolation
Pre-Integrate Volume Rendering: Past, Present, Future

11. Pre-Integration: The Present
important techniques published in 2004:
basics
perspective interpolation
partial pre-integration
accelerated pre-integration
incremental pre-integration of 2D tables
logarithmic scale of third dimension
pre-integrated volume lighting
Pre-Integrate Volume Rendering: Past, Present, Future

12. Pre-Integration: The Present
perspective interpolation
published by Kraus et al (Vis)
implements perspective correct interpolation of sampled data for projected tetrahedra
Pre-Integrate Volume Rendering: Past, Present, Future

13. Pre-Integration: The Present
partial pre-integration
published by Moreland, Angel 2004 (VolVis)
pre-integrates linear transfer functions
advantage:
tables are independent of transfer functions
disadvantage:
requires decomposition into linear segments
implemented for projection of tetrahedra
Pre-Integrate Volume Rendering: Past, Present, Future

14. Pre-Integration: The Present
incremental pre-integration of 2D tables
published by Lum et al (VisSym)
computes entries of 2D lookup tables incrementally along diagonals
can be combined with incremental integration in third dimension (sampling distance)
back
scalar
front scalar
Pre-Integrate Volume Rendering: Past, Present, Future

15. Pre-Integration: The Present
logarithmic scale of third dimension
published by Kraus et al (Vis)
pre-integrates 3D lookup table with entries for sampling distances 0, d, 2d, 4d, 8d, 16d, ...
uses a fragment program to access table
Pre-Integrate Volume Rendering: Past, Present, Future

16. Pre-Integration: The Present
pre-integrated volume lighting
published by Lum et al (VisSym)
pre-computes front-weighted and back-weighted transfer functions to interpolate lighting at front and back sampling point
front-weighted
back-weighted
front scalar
back scalar
Pre-Integrate Volume Rendering: Past, Present, Future

17. Pre-Integration: The Present
pre-integrated volume lighting (continued)
Pre-Integrate Volume Rendering: Past, Present, Future

18. Pre-Integration: The Present
current state of the art:
solutions for rendering artifacts available
efficient pre-integration available
combination with volume lighting available
conclusions:
pre-integrated volume rendering with 1D transfer functions is well understood
there are no excuses for bad rendering quality
Pre-Integrate Volume Rendering: Past, Present, Future

19. Pre-Integration: The Future
open problems / work in progress
multidimensional transfer functions
pre-integration in image plane
pre-integrated texture sampling
Pre-Integrate Volume Rendering: Past, Present, Future

20. Pre-Integration: The Future
multidimensional transfer functions
is a straight line the correct path of integration between (s1f,s2f) and (s1b,s2b)?
yes, for piecewise- linear data, e.g., in tetrahedral meshes s2
(s1b,s2b) ?
(s1f,s2f) s1
Pre-Integrate Volume Rendering: Past, Present, Future

21. Pre-Integration: The Future
multidimensional transfer functions (cont.)
but straight lines can cause problems:
“fine” sampling
“coarse” sampling s2 s2
s2iso
s2iso
point
missed s1 s1
s1iso
s1iso
Pre-Integrate Volume Rendering: Past, Present, Future

22. Pre-Integration: The Future
multidimensional transfer functions (cont.)
alternative approach: integrate over bounding box of each pair of sampling points
implementable with summed area tables (Green, GDC 2003) s2
s2iso
point
covered s1
s1iso
Pre-Integrate Volume Rendering: Past, Present, Future

23. Pre-Integration: The Future
pre-integration in image plane
problem: viewing rays might miss thin lines
pre-integration in the image plane might be able to catch them s2
s2iso s1
s1iso
Pre-Integrate Volume Rendering: Past, Present, Future

24. Pre-Integration: The Future
pre-integrated texture sampling
problem:
mip maps are good for pre-classification
no obvious solution for post-classification
approach:
apply pre-integration to the filtering
Pre-Integrate Volume Rendering: Past, Present, Future

25. Pre-Integration: The Future
conclusions:
next step: pre-integration for multidimensional transfer functions
pre-integration might be applicable to many more (filtered) sampling processes in computer graphics
Pre-Integrate Volume Rendering: Past, Present, Future