High-Quality Pre-Integrated Volume Rendering Using Hardware Accelerated Pixel Shading Klaus Engel, Martin Kraus, Thomas Er Visualization and Interactive Systems Group University of Stuttgart, Germany ggraph/Eurographics Workshop on Graphics Hardware 2
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High-Quality Pre-Integrated Volume Rendering Using Hardware Accelerated Pixel Shading
High-Quality Pre-Integrated Volume Rendering Using Hardware Accelerated Pixel Shading. Klaus Engel, Martin Kraus, Thomas Ertl Visualization and Interactive Systems Group University of Stuttgart, Germany. Siggraph/Eurographics Workshop on Graphics Hardware 2001. Motivation. - PowerPoint PPT Presentation
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High-Quality Pre-Integrated Volume Rendering Using Hardware Accelerated Pixel Shading
Klaus Engel, Martin Kraus, Thomas ErtlVisualization and Interactive Systems GroupUniversity of Stuttgart, Germany
Siggraph/Eurographics Workshop on Graphics Hardware 2001
Visualization and Interactive Systems Group,University of Stuttgart
Motivation
• Problems of texture-based volume graphics on PCs:– scientific visualization
• limited quality• 3D textures not commonly available• pre-classification shading
– computer games• high rasterization requirements
=> low performance• high texture memory requirements
Visualization and Interactive Systems Group,University of Stuttgart
Texture-based Volume Rendering
2D textures(axis-aligned
slices)
3D textures(view-aligned
Slices)
texturing(trilinear
interpolation)compositing
(blending)
texturing(bilinear
interpolation)compositing
(blending)
Visualization and Interactive Systems Group,University of Stuttgart
• render intermediate slices using multi-texture approach(Rezk-Salama,Engel et al., GH2000)
• But:– decreases rendering speed due to additional rasterization– many additional slices required even for low-resolution volumes – non-linear transfer functions:
not sufficient to sample volume with the Nyquist frequency of scalar data
Visualization and Interactive Systems Group,University of Stuttgart
Volume Classification
voxels
Post-classification
interpolation
interpolation
Pre-classification
classification
transfer functions
classification
Visualization and Interactive Systems Group,University of Stuttgart
Pre-Integrated Volume Rendering• Our approach:
– texture-based (2D/3D)– ray-segments computed in a pre-processing step– pre-computed ray-segment lookup (dependent texture)– small number of slices => fast
• Especially suited for:– low resolution volume data– non-linear transfer functions
Visualization and Interactive Systems Group,University of Stuttgart
Interactive Transfer Function Update
• 8 bit data: 256 x 256 = 65536 ray segments=> ~20 seconds on Athlon 650 (for constant ray segment length)
• 3 optimizations:– assume constant ray segment length– local modification of TF requires local update of DT– neglect self-attenuation within ray-segments and use
integral functions (as in Max et al., VolVis’90)
Visualization and Interactive Systems Group,University of Stuttgart
Results – Direct Volume Rendering
128 slicespre-
classification
128 slicespre-integrated
284 slicespost-
classification
128 slicespost-
classification
Visualization and Interactive Systems Group,University of Stuttgart
Results – Direct Volume Rendering, Random TF
Visualization and Interactive Systems Group,University of Stuttgart
Results - Isosurfaces
Visualization and Interactive Systems Group,University of Stuttgart
• 25 % slower than approach that used 1 or 2 texture fetches=> loopback in texture_shaders for 3rd and 4th fetch (2 clock cycles)
• Interactive transfer function update when neglecting self-attenuation
Visualization and Interactive Systems Group,University of Stuttgart
Problems
• artifacts in isosurfaces
• unequal ray segment lengths• only linear interpolation for each ray segment
• artifacts on volume boundaries• clipping planes front
sliceback slice
Visualization and Interactive Systems Group,University of Stuttgart
Conclusions• Pre-Integrated Volume Rendering
– High quality• even for small volumes• with small number of slices• with non-linear transfer functions• reproduces high frequencies in the transfer function