interactive high-quality volume rendering on flexible consumer graphics hardware klaus engel, martin...

Interactive High-Quality Volume Rendering

on Flexible Consumer Graphics Hardware

Interactive High-Quality Volume Rendering

on Flexible Consumer Graphics Hardware

Klaus Engel, Martin Kraus, Thomas ErtlVisualization and Interactive Systems GroupUniversity of Stuttgart, Germany

Graphiktag 2001 - Tübingen

Visualization and Interactive Systems Group,University of Stuttgart

Volume Data Sources

Measurements (CT,MRI)

Synthetic data(radial distance volume,

+ Perlin Noise)

Simulations (convection flow)


Volume Rendering - Physical Model

• Physics of light transport• Simplified to Volume Rendering Integral

• Transfer Function:Assigns opacity and color

• Discretization

0s

s

2

10

0 )(),(')'()()( 21),'(),(

0

s

s

s

s

ssss dssssdsesqesIsI

nss 1

n

i

n

ijjiin CsI

0 1

)1()(


Volume Rendering - Methods

indirect methods

isosurface reconstruction:huge amount ofpolygons

direct methods

ray-casting:huge amount oftrilinear interpolations


Texture-based Volume Rendering

2D textures(axis-aligned

slices)

3D textures(view-aligned

Slices)

texturing(trilinear

interpolation)

texturing(trilinear

interpolation)

compositing(blending)


texturing(bilinear

interpolation)

texturing(bilinear

interpolation)compositing(blending)



Problems - Axis Aligned Slices

Missing trilinearly interpolated slices

visual artifacts due tofixed number of slices

higher numberof slices

Undersampling Artifacts


Trilinear Interpolation using 2D Multi-Textures

Idea: Compute intermediate slices

Si

Si+1 bilinear interpolation bytexture environment

Si+α

Si+α = (1-α) Si + α Si+1

blending of two textures

Real trilinear interpolation

Efficient implementation using multitextures


Flexible PC Graphics Hardware – Multi-Textures

(modulate)

=

lightmaps onlylightmaps only decal onlydecal only

combined scenecombined scene

Light maps in Quake2Light maps in Quake2


Flexible PC Graphics Hardware – Register Combiners

rasterizationprimitiveassembly

texturefetching

textureenvironmentapplication

color sum

fogcoverage

application

texture unit 0

texture unit 1

registercombiners

final cmb

general cmb1

general cmb0


Flexible PC Graphics Hardware – Result

Cryoelectron-microscopic VolumeIsosurface of Escherichia Coli Ribosome at 18 Ångström

All data slices 10 times more slices


Higher Sampling Rates – Problem

• Discrete Approximation of Volume Rendering Integral will converge to correct result for d– According to Sampling Theorem sampling rate

must be greater than the Nyquist frequency– But: High frequencies in the Transfer Function may

considerably increase the required sampling rate

• Pre-Integrated Volume Rendering– Idea: Split numerical integration into

• one pre-integration for the transfer function• one integration for the scalar field

– Pre-Integrate Ray-Segments in a pre-processing step


Volume Rendering - Classification

voxels

Post-classification

interpolation

interpolation

Pre-classification

classification

transfer functions

classification


Pre-Integrated Volume Renderingslice-by-slice slab-by-slab

sb

sfsf

sb

fetch integral fromdependent texture

sbsf

pre-integrate all possible combinations

hardware-accelerated

implementation on NVidia GeForce3

chip

project slice

sf sb

front slice

back slice

texture polygon


Flexible Rasterization Hardware - Texture Shaders

rasterizationprimitiveassembly

texturefetching

textureenvironment

color sum

fog

coverageapplication

texture unit 0

texture unit 1

registercombiners

final cmbgeneral cmb1general cmb0

textureshaders


Flexible Rasterization Hardware - Texture Shaders• Texture Shaders (when enabled) replace the

standard OpenGL texture fetch mechanism

ARB_multitexture with NV_texture_shader

ARB_multitexture only

(s,t,r,q)0

(s,t,r,q)1

(s,t,r,q)2

(s,t,r,q)0

(s,t,r,q)1

(s,t,r,q)2

stage 0math & fetch

stage 1math & fetch

stage 2math & fetch

unit 0fetch

unit 1fetch

unit 2fetch

•With texture shaders, results from previous stages can affect the lookup of a subsequent stage


Pre-Integrated Volume Rendering

RGB1

(s2,t2,r2)

(1,0,0)

stage 2DOT_PRODUCT_NV

(1,0,0) • RGB1=sb

stage 2DOT_PRODUCT_NV

(1,0,0) • RGB1=sb

RGB0

(s3,t3,r3) (1,0,0)

stage 3DOT_PRODUCT_TEXTURE2D_NV

(1,0,0) • RGB0=sf

stage 3DOT_PRODUCT_TEXTURE2D_NV

(1,0,0) • RGB0=sf

RGBA result

on to register combiners

front slice

front slice

back slice

back slice

sbsb

stage 1TEXTURE_2D

stage 1TEXTURE_2D

(s1,t1)RGBA result

sfsf

stage 0TEXTURE_2D

stage 0TEXTURE_2D

(s0,t0)RGBA result

sb

sf


Pre-Integrated Volume Rendering - Isosurfaces

Isosurfaces:particular dependent texture

32 96 sf

sb

32

96

front slice

back slice

1.

1

front slice

back slice

4.

4front slice

back slice

2.

2

front slice

back slice

3.3

3a

3a


Results – Direct Volume Rendering

128 slicespre-

classification

128 slicespre-integrated

284 slicespost-

classification

128 slicespost-

classification


Results - Direct Volume Rendering – Random TF


Results - Isosurfaces


Results - Tooth data set


Conclusions

• Interactive High-Quality Volume Rendering on Consumer Graphics Hardware– Higher Sampling Rates Trilinear Interpolation using 2D Textures But: high rasterization requirements

– Better: Pre-Integration of Ray-Segments– Pre-Integration as general as post- and pre-

classification• already applied to cell projection (Roettger et al., Vis‘00)• can be applied to ray-casting as well


Pre-Integrated Volume Rendering Demo

Demo and Data Download:http://wwwvis.informatik.uni-stuttgart.de/~engel/pre-integrated/

interactive high-quality volume rendering on flexible consumer graphics hardware klaus engel, martin...

Documents

data slices

multitextures slide

quake2 slide

tbingen slide

s i s i

texture environment

color discretization

d textures axisaligned