Visualization Techniques: Advanced Volume Rendering

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Visualization TechniquesAdvanced Volume
Rendering
Day 3
Raphael Grasset
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Topics

• Interpolation
• Illumination and Non-Photorealistic Rendering
• Multimodal Rendering
• Advanced Transfer Functions

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Effects of Interpolation
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Effects of Interpolation
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Solution Pre-Integrated Classification
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Lighting Propagation in Volumes

• Until now we have considered transmission and
  emission of light in the volume (i.e. opacity,
  transparency)
• We can also have
• Reflection of the light (like with surface
  rendering)
• Scattering of the light
• This will give us shading, translucency and
  shadows

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Principle

• Need an estimation of the Gradient of the volume
• Precomputed before rendering (issue for
  time-varying data)

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Ambient Lighting
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Phong Shading Attenuation
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Refraction
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Reflections
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Shadows
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Translucency/Scattering
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Global Light Illumination
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Non-Photorealistic Rendering

• Not using a physical lighting model but rather
  techniques from art and media design
• Painting style
• Drawing style
• Cartoon Animation style
• Non Photorealistic Rendering vs Photorealistic
  Rendering

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Multimodal, Multichannel and Multivariate Volume
Rendering
Multimodal
Multichannel
Multivariate
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Multimodal Volume Rendering

• N volumes how to mix them?

accumulation level intermixing (CT MRI)
Image level intermixing (time varying data)
accumulation level intermixing (time varying data)
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Multichannel Volume Rendering

• Example cryosection of the Visible Human Project
• RGB slices? 3 scalars by voxels
• Conversion to another Color Space LUV

The u component (related to the chromatic change
in red-green colors)
The L component (related to brightness)
Gradients computed in Luv space, using the
second derivative along the gradient direction to
compute opacity.
Color difference gradient computed in RGB color
space
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Improving Transfer Function

• Histogram
• First Derivative

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Multi-Dimensional Transfer Function
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Automatic Algorithm

• Exhaustive Set of TF
• (offline processing)

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To Finish

• Graphics Card Capabilities have improved
  tremendously over the last decades
• A lot of computation can be done on your graphics
  card (General Processing GPU, GPGPU)
• Hardware Accelerated Volume Rendering (GPU
  Rendering)
• Development on the graphics card (GLSL, CUDA)

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Summary

• Interpolation Issues
• Real Time Lighting of Volume Rendering
• Use of Illustrative Techniques for Volume
  Rendering
• Guidance Interface for Transfer Function
• Real-Time Volume Rendering on your Desktop