Volumetric Rendering

What is it?
• Generally used for CT, MR imaging and
• 2D image is rendered from a 3D set of data or
• 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
– 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
Shear warping
Texture mapping
Combinations (combining techniques to
achieve better results)
Direct Volume Rendering Techniques
• 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
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
• 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
• 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)
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