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Helwig Hauser 1Two-level Volume Rendering
Helwig Hauserand Lukas Mroz
(VRVis Research Center)
Gian-Italo Bischi(University of Urbino)
M. Eduard Gröller(Vienna Univ. of Techn.)
Two-level Volume Rendering –fusing MIP and DVR
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IntroductionVolume Rendering:
Goal: insight into 3D dataChallenge: rendering projectionGood solutions: DVR, MIP, etc.(different advantages)Best approach depends on:
Data, structure of dataUser, visualization goals(regular goal: focus’n’context vis.)
Logical: combinations of texs.,like hybrid-rendering (surfs./DVR)
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Two-level Volume RenderingBasic Idea:
Prerequisite: segmentation into objectsLocal rendering, object-by-objectGlobal combination of representatives
Obj. 1 Obj. 2 Obj. 3 Obj. 2
DVR MIPMIP MIP DVR
DVR (five values only)
Viewing ray
local rend.
global rend.
local bufferglobal buffer
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Two-level Vol.-Rend. – ExampleBones, vessels: DVR
rather binary transfer functionsgood 3D impression
Skin: MIPrarely occludinguseful context
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Comparing DVR and MIPDVR:
strong influence: “thickness”spec. of TFs.: difficultpractical use: like surf. rend.3D impression, but occlusion
MIP:clear, sharp images (flat?!), one struct. of interest onlygood for complex objectsview-point variations neededwasting visual bandwidth?
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Application: MIP for contextFocus and Context:
well-known from information visualizationoften part of user goal (orientation)context should not distract, occlude view
Features of MIP:1 voxel thick everywhere ⇒ easy-to-control transparencyconcentrates on values of importance (proper transfer function needed)
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DVR vs. 2lVR 1/3All: DVR Skull, skin: MIP;
Vessels: DVR
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DVR vs. 2lVR 2/3All: DVR Bones, skin: MIP;
Arteries: DVR
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DVR vs. 2lVR 3/3All: DVR Context: MIP;
Organs: DVR
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Dynamical System VisualizationOriginal Application:
game theory, econometricsdiscrete dynamical systems (maps)focus on:
attractorsbasins of attractionspatial inter-relation of basinscritical surfaces
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Two-level Volume RenderingOuter basin: MIP Attractor: MIP
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Interactive Rendering 1/2Shear-warp rendering:
no inter-voxel interpolation ⇒ fast!intermediate plane: two buffers(local, global) bi-linear warp
Reversed storage scheme:objects: stack of slices (varying z)slice: list of voxels (explicit x, y, etc.)re-ordering within slice: arbitrary clippingpreprocessing, 3 copies of data: x, y, z
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Interactive Rendering 2/2renderListEntry[pvd,obj,z]:
list of all voxels of obj. objwhich share depth value z(principal viewing dir. pvd)object-opacity, z, clipping
Features:free space leaping,free clipping planes
Quantized Gradients ⇒ LUT for shadingJava-Impl. on PC (AMD Athlon 600)
x,y,...firstlastendz,α, ...
voxel data
clipped
active
renderListEntry
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Further ExtensionsColor ≈ basin vicinity Opacity ≈ basin vicinity
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Live demo
by Lukas Mroz
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SummaryNew approach to fuse different volume rendering techniquesTwo-level approach: rendering locally and globally in parallelUseful application: focus’n’contextInteractive Implementation:
Reversed Storage SchemeShear-Warp Factorization, no interpolationQuantized Gradients~256³ ⇔ ~170ms (600MHz PC)
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ConclusionsFocus’n’context: important for scientific visualization!DVR good for low-frequency objects, 3D,but: over-loaded imagesMIP good for complex objects & context,but: flat without anims.Two-level Volume Rendering: arbitrary local rendering (nonphotorealistic rend.)No optimal approach per se,interaction very important for visualization
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AcknowledgementsThanx go to:
BandViz (FWF-funded project #P12811)Helmut Doleisch, Thomas TheußlVisMed (FFF-funded project)Innsbruck Univ. Hospital (medical datasets)
and thank you for your attention!
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