Virtual Painting.

Transcription

1 Virtual Painting

2 Digital Painting 2 Alvy Ray Smith and Ed Ernshwiller working on Paint, 1979 Many advantages Undo mistakes Perfect copies Unlimited reprints No material cost No drying No fading or decay No physical limits

3 Traditional Painting Rich, dynamic behavior Deformable brushes Fluid paint Intuitive control 3D input Visual and haptic feedback The process The dispatch with which a number of effects can be obtained by a direct, simple technique Mayer 1991, The Artist s Handbook 3

4 Goal Enable realistic interactive painting on computer with thick medium using realistic 3D brushes 4

5 Applications Training Education Entertainment Production 5

6 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 6

7 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 8/27/04 7

8 Problem Overview Brush Complex geometry Stiff dynamical system Paint Complex surface Complex behavior Subsurface scattering Haptics Needs stability Needs khz updates Interaction Canvas Brush contact Canvas Brush transfers Integration All simulations must work interactively simultaneously 8

9 Natural Media Chu & Tai 2002 Xu, et al Curtis et al Rudolf et al Corel Painter 8, Sousa, 1999

10 Brush Simulation Strassman, 1986 Wong & Ip, 2000 Chu & Tai, 2003 Xu et al., 2003,2004 Only for ink painting Specialized geometry Lower stiffness No real bristles No paint pickup Some not interactive 10

11 System Context 11

12 Input 12

13 Brush Simulation 13

14 Paint Simulation 14

15 Paint Rendering 15

16 System Overview 16

17 System Demonstration v=tzq-cpezm8q 17

18 Brush Modeling Geometric modeling Brush has 1,000 s of hairs Each interacts with paint & roughness/tooth of canvas Dynamic simulation Each hair deformable and independent Bristles have stiff dynamics 18

19 Geometric Modeling Exploit bristle coherence Define skeletal spine bristles Deform surface or interpolate bristles For smoother, neater marks For coarser, rougher marks 19

20 Brush Spine Dynamics Stiff dynamical system Force large, mass small Numerical integration requires small timestep 20

21 Minimization Approach Brush always at equilibrium so A statics problem Or quasi-static since Energy min Use standard, robust minimizer E.g. Quasi-Newton SQP (Sequential Quadratic Programming) 21

22 Brush Energy Minimization Minimize where Spring energy Friction loss Subject to 22 Damping loss

23 Brush Modeling Results 23

24 System Demonstration Video 24

25 dab Paint Simulation Fast and simple 2D paint behavior Modest system requirements First bi-directional brush transfer First complex loading 25

26 Complex brush loading Enabled by 3D brush model + bi-directional transfer Virtual Painting An essential technique in traditional painting Difficult previously Useful component of interface 26

27 dab Result Images 27

28 Frog Rebecca Holmberg

29 Apple Sarah Hoff

30 Meadow Rebecca Holmberg

31 Man Lauren Adams

32 Blossoms Eriko Baxter

33 Road Bug Rebecca Holmberg

34 Fluid Motion Steps: Determine velocity field Advect material 34

35 Simulating Paint - Velocity Paint is a Viscous / Viscoplastic Fluid acceleration advection pressure viscosity elasticity incompressibility Subject to boundary conditions 35

36 Material Advection Given velocity field v, move material according to the advection equation: Material = Pigment & field Semi-Lagrangian advection 36

37 System Demonstration Video 37

38 Viscous Result Images 38

39 Woman in a Hat Eriko Baxter

40 Field of Flowers Eriko Baxter

41 The Beach Andrea Mantler

42 Meadow Haolong Ma

43 Abstract I John Holloway

44 IMPaSTo Paint Dynamics Paint is very complex IMPaSTo strategy: Model dominant terms 44

45 2.5D Representation Cross section of Monet s Water Lillies 45 (Courtesy The Museum of Modern Art)

46 Simulating Paint - Velocity Paint is a Viscous / Viscoplastic Fluid acceleration advection pressure viscosity elasticity incompressibility Subject to boundary conditions 46

47 Paint Color Pigmented material Subsurface scattering Mixes nonlinearly: Composites nonlinearly: Kubelka-Munk model (1948,1954) 100% + 0% = 50% = (1-a) + a 47

48 Measurement Data collection setup 5600K Illuminant SpectraScan PR

49 49 R G B Spectral Sampling Canvas Reflectance Light Spectrum = Use 8 wavelengths Sufficient (Duncan, 1949) Efficient on GPU Gaussian quadrature Choose best 8 at runtime Red Green Blue

50 Color Mixing Results 50

51 System Demonstration Video 51

52 IMPaSTo Result Images 52

53 Ajisai Eriko Baxter

54 Woman Andrea Mantler

55 Dame en Blau Heather Wendt

56 Gogh Studios Room 1 William Baxter

57 Green Eriko Baxter

58 Abstract III John Holloway