a hardware-assisted hybrid rendering technique for interactive volume visualization brett wilson...
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A Hardware-Assisted Hybrid Rendering Technique for Interactive Volume Visualization
Brett Wilson
Kwan-Liu MaUniversity of California, Davis
Patrick S. McCormickLos Alamos National Laboratory
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Overview
Problems with large-scale volume visualization Hybrid rendering
– Hybrid data generation– Storage– Rendering
Results Future work
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Large-scale volume visualization
Data: Resolutions are 5123 (128MB) and higher
Commodity PC: 1GB RAM, 128MB video memory
Want to display large data on these small computers
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Combine volume and point rendering
Large, slowly varying regions– Hardware volume rendering
Small areas of high detail– Point-based rendering
Combine the efficiency of both rendering techniques
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Selected previous work
Hardware volume rendering [Cabral 1994] [Wilson 1994]– Multi-resolution [LaMar 1999] [Weiler 2000]– Parallel [Kniss 2001] [Lum 2001] [Lum 2002]
Splatting [Westover 1989]– Extensions [Mao 1996] [Mueller 1999]– EWA Volume Splatting [Zwicker 2001][Ren 2002]
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Generating hybrid data
Low-resolutionvolume
Originalvolume
Generatedpoints
Region ofhigh error
Generating low-resolutionvolume data
Generating points forregions of high error
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Point selection
Error evaluated on a regular grid– Usually same resolution as original data
Points generated where error is above a given threshold– Also allows goal-oriented generation
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Hybrid data generation overview
Original data
Low-res volume data Point data
(interpolation)
(difference &threshold)
Result data
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Rendering opaque features
Original vol. HybridLow-res vol. Point data
+ =
• Points enhance boundary of opaque feature
• Transparent area can’t be made more transparent
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Rendering transparent features
Original vol. HybridLow-res vol. Point data
+ =
• Points enhance boundary of opaque surroundings
• Transparent feature can’t be made more transparent
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Dealing with overestimation errors
Most important features usually drawn as opaque– Effect minimized
Pick a low-resolution volume that is always more transparent than the original– Limits transfer functions– Requires a lot of points
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Rendering volumetric data
Texture-mapped polygonsrendered back-to-front
Eye
Result is the illusion of volume
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Computing volume appearance
Color/opacity– Paletted texture lookup for
transfer function value
Lighting– Paletted texture lookup for
specular/diffuse
Register combiners
Result
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Rendering hybrid data
Slices of pointsare interleavedwith polygons
Eye
Each slice of pointsis loaded into a display list.
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Computing point appearance
Color/opacity– Paletted texture lookup for
transfer function value
Lighting– Paletted texture lookup for
specular/diffuse
Scale by error value– Map into transfer-function
space with 2D texture lookup
Register combiners
Result
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Hybrid data storage
Volumetric data– 1 byte value– 1 byte normal
Point data– 3 to 6 byte position (depending on grid resolution)– 1 byte original value– 1 byte normal – 1 byte error
Space: 5123 = 2563 + 26 M points
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Results
Simulation– Argon bubble simulation, [Lawrence Berkeley National Lab]
Medical– MRI of a human chest, [Kubota Co., Japan]
Mechanical– Furby® (mechanical toy) CT scan, [Los Alamos/Hytec]
Test machine:– 1GHz Pentium III Xeon, 1GB RAM, 128MB GeForce 4 Ti 4600
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Results: 5123 Argon bubble simulation
Area of focusFull frame(one of a time-varying simulation)
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Results: 5123 Argon bubble simulation
Original:5123 268MB
Low-res volume:2563
33MB
Hybrid:2563 + 361K points37MB(1/64 error threshold)
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Results: 5123 Chest MRI
211283+11M
Hybrid 1283 + 4M points1/12 error threshold, 5123 grid40MB0.29 s/frame
1283 volume4MB0.01 s/frame
5123 volume268MB0.35 s/frame
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Hybrid 2563 + 7M points1/64 error threshold, 5123 grid97MB0.47 s/frame
2563 volume33MB0.04 s/frame
5123 volume268MB0.35 s/frame
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Results: 512 512 2048 Furby®
Mechanical data– Many sharp edges– Very high dynamic range– Very high resolution
Full size = 1 GB (including normals)
Non-square voxels
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Results: 512 512 2048 Furby®
2563 33MB0.07 s/frame
2563 + 3M points (5123, 1/16 error)
59MB0.36 s/frame
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Results: 512 512 2048 Furby®
2563 + 3M points (5123, 1/16 error)
59MB0.36 s/frame
2563 + 4.7M points (10243, 1/8 error)
71MB0.58 s/frame
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Future enhancements
Non-cubic error sampling interval– View dependent
Automatic parameter selection
Optimize point size/opacity
Incremental point loading and rendering
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Conclusions
New way to reduce data size for previewing– Preserves fine details
Allows very large data to be viewed on small computers– Acceptable performance
Effective for simulation, medical, and mechanical data
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Acknowledgements
Los Alamos National Laboratory DOE SciDAC NSF contract ACI 9983641 (PECASE Award) LSSDSV contract ACI 9982251
Data– Argon bubble: Center for Computational Sciences and
Engineering at the Lawrence Berkeley National Laboratory
– Chest MRI: Dr. H. Miyachi at Kubota Co., Japan
– Furby®: Anthony Davis at Hytec Inc. and
Bill Ward of the Los Alamos National Laboratory