Computer Graphics Computer Graphics Research at VirginiaResearch at Virginia

David LuebkeDavid Luebke

Department of Computer ScienceDepartment of Computer Science

Outline

My current research– Perceptually Driven Interactive Rendering

Perceptual level of detail control Wacky new algorithms

– Scanning Monticello

Graphics resources– Building an immersive display– Building a rendering cluster?

Perceptual Rendering

Next few slides from a recent talk Apologies to UVA vision group

Perceptually Guided Interactive Rendering

David Luebke

University of Virginia

Motivation:Stating The Obvious

Interactive rendering of large-scale geometric datasets is important– Scientific and medical visualization– Architectural and industrial CAD– Training (military and otherwise)– Entertainment

Motivation:Model Size

Incredibly, 3-D models are getting bigger as fast as hardware is getting faster…

Courtesy General Dynamics, Electric Boat Div.

Big Models:Submarine Torpedo Room

1994: 700,000 polygons

(Anonymous)

Big Models:Coal-fired Power Plant

1997:13 million polygons

1998:16.7 million polygons

Big Models:Plant Ecosystem Simulation

Deussen et al: Realistic Modeling of Plant Ecosystems

Big Models:Double Eagle Container Ship

2000:82 million polygons

Courtesy Newport News Shipbuilding

Big Models:The Digital Michelangelo Project

2000 (David):56 million polygons

2001 (St. Matthew):372 million polygons

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(Part Of) The Solution:Level of Detail

Clearly, much of this geometry is redundant for a given view

The idea: simplify complex models by reducing the level of detail used for small, distant, or unimportant regions

Traditional Level of DetailIn A Nutshell…

249,924 polys 62,480 polys 7,809 polys 975 polys

Courtesy Jon Cohen

Create levels of detail (LODs) of objects:

Distant objects use coarser LODs:

Traditional Level of DetailIn A Nutshell…

The Big Question

How should we evaluate and regulate the visual fidelity of our simplifications?

Measuring Fidelity

Fidelity of a simplification to the original model is often measured geometrically:

METRO by Visual Computing Group, CNR-Pisa

Measuring Visual Fidelity

However…– The most important measure of fidelity is usually not

geometric but perceptual: does the simplification look like the original?

Therefore:– We are developing a principled framework for LOD in

interactive rendering, based on perceptual measures of visual fidelity

Perceptually Guided LOD: Questions And Issues

Several interesting offshoots:– Imperceptible simplification

When can we claim simplification is undetectable?

– Best-effort simplification How best to spend a limited time/polygon budget?

– Silhouette preservation Silhouettes are important. How important?

– Gaze-directed rendering When can we exploit reduced visual acuity

Related Work:Perceptually Guided Rendering

Lots of excellent research on perceptually guided rendering

But most work has focused on offline rendering algorithms (e.g., path tracing)– Different time frame!

Seconds or minutes vs. milliseconds

– Sophisticated metrics: Visual masking, background adaptation, etc…

Perceptually Guided LOD: Our Approach

Approach: test folds (local simplification operations) against a perceptual model to determine if they would be perceptible

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Fold

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Perception 101:The Contrast Sensitivity Function

Perceptual scientists have long used contrast gratings to measure limits of vision:– Bars of sinusoidally

varying intensity– Can vary:

Contrast Spatial frequency Eccentricity Velocity Etc…

Perception 101: The Contrast Sensitivity Function

Contrast grating tests produce a contrast sensitivity function– Threshold contrast

vs. spatial frequency– CSF predicts the

minimum detectablestatic stimuli

Campbell-Robson Chart by Izumi Ohzawa

Your Personal CSF

Framework: View-Dependent Simplification

Next: need a framework for simplification– We use view-dependent simplification for

LOD management Traditional LOD: create several discrete LODs in a

preprocess, pick one at run time View-dependent LOD: create data structure in

preprocess, extract an LOD for the given view

View-Dependent LOD: Examples

Show nearby portions of object at higher resolution than distant portions

View from eyepoint Birds-eye view

View-Dependent LOD: Examples

Show silhouette regions of object at higher resolution than interior regions

View-Dependent LOD: Examples

Show more detail where the user is looking than in their peripheral vision:

34,321 triangles

View-Dependent LOD: Examples

Show more detail where the user is looking than in their peripheral vision:

11,726 triangles

View-Dependent LOD:Implementation

We use VDSlib, our public-domain library for view-dependent simplification

Briefly, VDSlib uses a big data structure called the vertex tree– Hierarchical clustering of model vertices – Updated each frame for current simplification

The Vertex Tree:Region Of Effect

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Fold Node A

Unfold Node A

Folding a node affects a limited region:

– Some triangles change shape upon folding– Some triangles disappear completely

Wacky New Algorithms

I am interested in exploring new perceptually-driven rendering algorithms– Don’t necessarily fit constraints of today’s

hardware Ex: frameless rendering Ex: I/O differencing (time permitting)

– Give the demo, show the movie…

Non-Photorealistic Rendering (time permitting)

Fancy name, simple idea:

Make computer graphics that don’t look like computer graphics

Non-Photorealistic Rendering

Fancy name, simple idea:

Make computer graphics that don’t look like computer graphics

Non-Photorealistic Rendering

Fancy name, simple idea:

Make computer graphics that don’t look like computer graphics

NPRlib

NPRlib: flexible callback-driven NP rendering

Bunny: Traditional CG Rendering

Non-Photorealistic Rendering

Bunny: Pencil-Sketch Rendering

NPRlib: flexible callback-driven NP rendering

Non-Photorealistic Rendering

Bunny: Charcoal Smudge Rendering

NPRlib: flexible callback-driven NP rendering

Non-Photorealistic Rendering

Bunny: Two-Tone Rendering

NPRlib: flexible callback-driven NP rendering

Non-Photorealistic Rendering

Bunny: Two-Tone Rendering

NPRlib: flexible callback-driven NP rendering

Scanning Monticello

Fairly new technology: scanning the world

Scanning Monticello

Want a flagship project to showcase this Idea: scan Thomas Jefferson’s Monticello

– Historic preservation– Virtual tours– Archeological and architectural research,

documentation, and dissemination– Great driving problem for scanning & rendering

research Results from first pilot project.

– Show some data…

Scanning Monticello

Scanning Monticello

Graphics Resources

2 SGI Octanes– Midrange graphics hardware

SGI InfiniteReality2

– 2 x 225 MHz R10K, 1 Gb, 4 Mb cache– High-end graphics hardware: 13 million triangles/sec,

64 Mb texture memory Hot new PC platforms (P3s and P4s)

– High-end cards built on nVidia’s best chipsets– Stereo glasses, digital video card, miniDV stuff– Quad Xeon on loan

Software! – Maya, Renderman, Lightscape, Multigen, etc.

Graphics Resources

Building an immersive display– NSF grant to build a state-of-the-art

immersive display: 6 projectors, 3 screens, passive stereo High-end wide-area head tracker 8 channel spatial audio PCs to drive it all

– Need some help building it…

Graphics Resources

Building a rendering cluster?– Trying to get money to build a high-end

rendering cluster for wacky algorithms 12 dual-Xeon PCs:

1 Gb RAM 72 Gb striped RAID nVidia GeForce3

Gigabit interconnect

– Don’t have the money yet, but do have 6 hot Athlon machines

More Information

I only take students who’ve worked with or impressed me somehow– Summer work: best– Semester work: fine, but harder

Interested in graphics? – Graphics Lunch: Fridays @ noon, OLS 228E– An informal seminar/look at cool graphics

papers– Everyone welcome, bring your own lunch