Volumetric Rendering


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.

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

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

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

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

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

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

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

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!!!)

Shear-Warp (cont’d)

Full Image Order

• • • Another class of volume ray casting More complex with data handling and buffering More multiplications to achieve the interpolations needed

Texture Mapping

• • • Similar to full image order Applied to the surface of a shape or polygon Used with texture mapping hardware

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

Misc. Techniques (cont’d)

• • Level of detail volume rendering – Similar to texture mapping Examples: Translucency and stippling

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……

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

Ultrasound Example

Animated Examples

Animated Examples (cont’d)