Interactive Rendering of Large Volume DataSets (IEEE Viz 2002)

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Interactive Rendering of Large Volume DataSets
(IEEE Viz 2002)
Stefan Guthe,WSI/GRIS, University of Tubingen
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Summary

• Data is stored using multires octree
• Wavelet compression wavelet coefficients are
  further compressed
• At render time, the data is decompressed on the
  fly and rendered using 3D texture hardware
• Rendering is done according to view dependent
  priority
• Good frame rates but final image size is low
  (256 256)

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Wavelet compression

• The compression involves 2 steps wavelet
  representation of data and huffman, run-length or
  arithmetic encoding to further reduce space for
  wavelet coefficients
• Compression ratio of huffman encoding (used in
  the implementation) is 341 for lossless
  compression

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Projective classification and rendering

• A projective classification eliminates rendering
  voxels not in the view frustum
• View dependent priority is assigned to nodes
  depending on their voxel depths
• The number of voxels that can be displayed is
  preset (depending on texture memory)
• A priority queue is used to insert node by node
  of the octree, the closer voxel nodes having
  higher priority

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Rendering with priority

• The node with higher priority in the queue is
  fetched
• Its high frequency wavelet coefficients are
  decompressed and the child is inserted in the
  queue
• This process halts when the number of voxels
  exceed the preset limit

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Trilinear interpolation and block size effects

• The volume is decomposed hierarchically into k3
  (usually k16) blocks, which are rendered as 3D
  textures using hardware
• Block size must be a power of 2, because of
  OpenGL texture restrictions
• The target image is 256256 pixels For all
  256256 possible values of entry and exit, volume
  integrals are pre-computed
• Tri-linear interpolation done by texture hardware
  might need multiple blocks in the octree
  therefore neighboring blocks in the octree might
  have to be coalesced
• A greater block size (k 32) reduces this
  overhead

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Caching

• Caching of decompressed data is required for
  interactive frame rates. Unaddressed issues
  Interpolating between multiple resolutions,

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Results

• Visible human dataset
• 2048 X 1216 X 1877 X 12 bit (6.4 G)
• Final image size rendered is 256 X 256
• Frame rate vs compression ration vs PSNR