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The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL 1 .
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The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL http :// gamma.cs.unc.edu/DAB http://gamma.cs.unc.edu/IMPASTO http://gamma.cs.unc.edu/VISCOUS http://gamma.cs.unc.edu/BRUSH Virtual Painting
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Transcript of The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL 1 .
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
1
http://gamma.cs.unc.edu/DAB
http://gamma.cs.unc.edu/IMPASTO
http://gamma.cs.unc.edu/VISCOUS
http://gamma.cs.unc.edu/BRUSH
Virtual Painting
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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Digital Painting
Alvy Ray Smith and Ed Ernshwillerworking on “Paint”, 1979
Many advantages• Undo mistakes• Perfect copies• Unlimited
reprints• No material cost• No drying• No fading or
decay• No physical limits
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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Traditional Painting
“The dispatch with which a number of effects can be obtained by a direct, simple technique” – Mayer 1991, The Artist’s Handbook
Rich, dynamic behaviorDeformable brushesFluid paint
Intuitive control3D inputVisual and haptic feedback
The process
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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GoalEnable realistic interactive painting on computer with thick medium using realistic 3D brushes
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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Applications
Training
Education
Entertainment
Production
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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Artist’s Quote
“My artist's toolbox has oils and acrylics—and a computer. But the computer’s not tactile, and I miss that. You can't push junk around.”
– Tia, Pixar Animation Studios
http://www.pixar.com/artistscorner/tia/interview.html
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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Artist’s Quote
“I have used painter and psp [Paint Shop Pro] for a few yrs, and would welcome something better, would fight for, would almost die for a program like is described.”
--received by email 8/27/04
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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Problem OverviewBrush
Complex geometryStiff dynamical system
PaintComplex surfaceComplex behaviorSubsurface scattering
HapticsNeeds stabilityNeeds kHz updates
InteractionCanvas Brush contactCanvas Brush transfers
IntegrationAll simulations must work interactively simultaneously
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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Natural Media
Rudolf et al. 2003Rudolf et al. 2003
Curtis et al. 1997Curtis et al. 1997
Xu, et al. 2003Xu, et al. 2003Chu & Tai 2002Chu & Tai 2002
Corel Painter 8, 2003Corel Painter 8, 2003
Sousa, 1999Sousa, 1999
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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Brush Simulation
Strassman, 1986Strassman, 1986
Wong & Ip, 2000Wong & Ip, 2000
Chu & Tai, 2003Chu & Tai, 2003
Xu et al., 2003,2004Xu et al., 2003,2004
Only for ink painting Specialized geometryLower stiffnessNo real bristlesNo paint pickupSome not interactive
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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System Context
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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Input
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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Brush Simulation
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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Paint Simulation
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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Paint Rendering
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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System Overview
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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System Demonstration
http://www.youtube.com/watch?v=tZq-cpeZm8Q
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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Brush ModelingGeometric modeling
Brush has 1,000’s of hairsEach interacts with paint & roughness/tooth of canvas
Dynamic simulationEach hair deformable and independentBristles have stiff dynamics
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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Geometric Modeling
Exploit bristle coherenceDefine skeletal “spine” bristlesDeform surface or interpolate bristles
For smoother, neater marks For coarser, rougher marks
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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Brush Spine Dynamics
Stiff dynamical systemForce large, mass smallNumerical integration requires small timestep
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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Minimization Approach
Brush always at equilibrium so
A statics problemOr quasi-static since
Energy minUse standard, robust minimizer
E.g. Quasi-Newton SQP(Sequential Quadratic Programming)
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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Brush Energy Minimization
Minimize
where
Subject to
Spring energy
Friction loss
Damping loss
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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Brush Modeling Results
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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System Demonstration
Video
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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dAb Paint Simulation
Fast and simple2D paint behaviorModest system requirementsFirst bi-directional brush transferFirst complex loading
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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Complex brush loading
Enabled by 3D brush model + bi-directional transferAn essential technique in traditional paintingDifficult previouslyUseful component of interface
Virtual Painting
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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dAb Result Images
Frog
Rebecca Holmberg
Apple
Sarah Hoff
Meadow
Rebecca Holmberg
Man
Lauren Adams
Blossoms
Eriko Baxter
Road Bug
Rebecca Holmberg
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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Fluid Motion
Steps:Determine velocity fieldAdvect material
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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Simulating Paint - Velocity
Paint is a Viscous / Viscoplastic Fluid
Subject to boundary conditions
advection pressure viscosity elasticity
incompressibility
acceleration
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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Material Advection
Given velocity field v, move material according to the advection equation:
Material = Pigment & fieldSemi-Lagrangian advection
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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System Demonstration
Video
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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Viscous Result Images
Woman in a Hat
Eriko Baxter
Field of Flowers
Eriko Baxter
The Beach
Andrea Mantler
Meadow
Haolong Ma
Abstract I
John Holloway
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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IMPaSTo Paint Dynamics
Paint is very complex
IMPaSTo strategy:Model dominant terms
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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2.5D Representation
Cross section of Monet’s Water Lillies
(Courtesy The Museum of Modern Art)
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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Simulating Paint - Velocity
Paint is a Viscous / Viscoplastic Fluid
Subject to boundary conditions
advection pressure viscosity elasticity
incompressibility
acceleration
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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Paint Color
Pigmented material Subsurface scattering
Mixes nonlinearly:Composites nonlinearly:
Kubelka-Munk model (1948,1954)
100% 0%+ = 50%
= + a (1-a)
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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Measurement
Data collection setup
SpectraScan PR-715
5600K Illuminant
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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Spectral Sampling
Use 8 wavelengthsSufficient (Duncan, 1949)Efficient on GPU
Gaussian quadratureChoose best 8 at runtime
CanvasReflectance Light Spectrum
Red
Green
Blue
R
G
B=
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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Color Mixing Results
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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System Demonstration
Video
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
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IMPaSTo Result Images
Ajisai
Eriko Baxter
Woman
Andrea Mantler
Dame en Blau
Heather Wendt
Gogh Studios Room 1
William Baxter
Green
Eriko Baxter
Abstract III
John Holloway
