Volumetric Rendering

1. 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)