1. Graphics and Multimedia
Volumetric Rendering
Tessa Adderley
Graphics and Multimedia
CS6783

2. What is it? Generally used for CT, MR imaging and Ultrasounds
2D image is rendered from a 3D set of data or array
Mostly used in medical applications but is also used in:
Car Part manufacturing
Scientific rendering: chemistry, entomology, rtc.

3. How many ways can you do it?
Early approaches really had some problems:
Distance between sections created faulty rendering
Branching sections caused distortion
Researchers sought to eliminate this by
Cuberille technique
Marching Cubes
Dividing Cubes

4. How many ways can you do it? (cont’d)
After finding these methods had problems too researchers sought to find a way to directly render the data.
Additive re-projection technique
Source-attenuation re-projection technique
Depth shading algorithms
Radiation transport equations
Low-albedo/single scattering approximations

5. There’s more ways?
After seeing that Direct Volume Rendering was the way to go researchers found various ways to achieve it.
Main idea is the volume rendering integral
Evaluated based on a certain simplification

6. Direct Volume Rendering Techniques
Volume ray casting
Splatting
Shear warping
Texture mapping
Combinations (combining techniques to achieve better results)

7. Direct Volume Rendering Techniques (cont’d)
Other miscellaneous:
Gaze-directed volume rendering
Level-of-detail volume rendering
Non-photorealistic volume rendering
Interactive translucent volume rendering

8. Volume Ray Casting Different from ray casting
Derived from graphic rendering equation
Begins just as with regular volume rendering
Good, but slow
Has been combined with the Shear warp to produce better resulting images

9. Splatting? What?!? Does just what it says…… Uses pre-shaded scheme
Projected as a fuzzy ball
Its 2D screen projection is called a “splat”, or a “footprint”
splat vs VRC

10. Shear-Warp? What?!? One of the fastest techniques Three steps:
The “shear”
The intermediate image
The “warp”
That “warp” might not be such a great idea after all……. (full-image is bettteeerrrr!!!)

11. Shear-Warp (cont’d)

12. Full Image Order Another class of volume ray casting
More complex with data handling and buffering
More multiplications to achieve the interpolations needed

13. Texture Mapping Similar to full image order
Applied to the surface of a shape or polygon
Used with texture mapping hardware

14. Misc. Techniques Gaze-directed volume rendering
Allowed generation of images with varying resolution
Interactive translucent volume rendering
Rendered volumetric shadows as well as the appearance of translucency
Non-photorealistic rendering using stippling
Simulate stipple drawing

15. Misc. Techniques (cont’d)
Level of detail volume rendering
Similar to texture mapping
Examples: Translucency and stippling

16. Applications: Is there anything else other than medical ones?
Computed Tomography (CT scans)
Shaded image
Un-shaded image
Magnetic Resonance imaging (MRI)
Better at tissue stuff……
Navigation through someone’s colon
Hopefull not mine……

17. Applications: Is there anything else other than medical ones?
Ultrasounds 3D/4D
Fetal examinations
Puncture procedures
Can be limited if there isn’t enough amniotic fluid

18. Ultrasound Example

19. Animated Examples

20. Animated Examples (cont’d)