Multi-Dimensional Transfer Functions for Interactive Volume Rendering

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Multi-Dimensional Transfer Functions for
Interactive Volume Rendering Interactive Volume
Rendering Using Multi-Dimensional Transfer
Functions, etc.
by Kniss, Kindlmann, Hansen University of Utah
presentation by Nicholas Schwarz schwarz_at_evl.uic.e
du Electronic Visualization Lab University of
Illinois at Chicago
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Introduction

• Easy to find objects in spatial domain, but
  difficult to do so in transfer function domain.
• Different regions may have same scalar value.
• Enormous degrees of freedom.
• Small changes in transfer function result in
  drastic/unexpected changes in the visualization.

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Multi-Dimensional Transfer Functions

• Gradient local rate of change (1st derivative)

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Multi-Dimensional Transfer Function

• Hessian second partial derivative

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Multivariate Data
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Hardware

• Dependent texture reads use color fragments to
  generate texture coordinates, replace those color
  fragments with corresponding entries from a
  texture.
• Classification can get vary large for
  multi-dimensions, so higher dimensions are
  limited.
• Surface shading cube map dependent texture reads
  treat RGB component as a vector used as texture
  coordinates for a cub map. Bad for shading
  homogeneous regions, but good for boundaries.

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Hardware

• Shadows off screen render buffer to accumulate
  the amount of light.

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Nifty Widget