D animation. Advantages of 2-D2. Advantages of 3-D3. Related work. Key idea. Applications of Computer Graphics in Cel Animation.

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1 Page 1 Applications of Computer Graphics in Cel Animation 3-D D and 2-D 2 D animation Adam Finkelstein Princeton University COS 426 Spring 2003 Homer 3-D3 Homer 2-D2 Advantages of 3-D3 Complex lighting and shading Reuse from scene to scene Automatic in-betweening Ease of camera motion Realism Texture mapping Advantages of 2-D2 Easier for traditional animators Simple gestures convey emotion Art form refined for 80 years Key idea Use 3-D 3 D methods in 2-D 2 D animation! Expressiveness of 2-D2 Technical benefits of 3-D3 Related work Automating cel animation pipeline [Fekete 95, Robertson 94, Shantzis 94, Wallace 81] Hybrid 2D/3D for cel animation [Rademacher 99, Williams 91]

2 Page 2 Two forms of art work Overview Introduction Multiperspective panoramas Texture mapping Shadows Multiperspective Panoramas for Cel Animation Daniel Wood Adam Finkelstein John Hughes Craig Thayer David Salesin University of Washington Princeton University Brown University Disney Feature Animation [SIGGRAPH '98] [Pinocchio,, 1940] Suggesting a moving camera A multiperspective panorama incorporates many perspectives into a single locally coherent image. A moving window slides across the panorama, selecting frames for the animation.

3 Page 3 Objective Given: 3D model and camera path Create: Panorama and moving window such that the 2D animation resembles the 3D animation 1. 3-D 3 D scene and camera path 2. Panorama and moving window 3. Illustrated panorama 4. Extracted frames 5. CG Elements

4 Creating a panorama Take snapshots of 3D scene Arrange snapshots in a plane Merge snapshots into single image Take snapshots Arrange Arrange snapshots snapshots Merge Merge snapshots snapshots Arrange consecutive snapshots Sample Sample points points from from first first snapshot snapshot Find Find corresponding corresponding points points on on second second snapshot snapshot Align Align snapshots snapshots using using aa transform transform Find corresponding points Page 4

5 Untrimmed Trimmed Align snapshots Limitations HandHanddesigned Panoramas Panoramas cannot cannot do do itit all all ((e.g., e.g., e.g., circling circling centerpiece centerpiece of of table) table) Our Our method method does does not not do do itit all all ((e.g., e.g., e.g., Beauty Beauty and and the the Beast Beast library) library) Automatic Page 5

6 Page 6 Strengths Wide variety of camera motion Easy experimentation Easy CG integration Illustrator creates detail Hand-drawn drawn artistic style Texture Mapping for Cel Animation Wagner Corrêa Rob Jensen Princeton University Craig Thayer Disney Feature Animation Adam Finkelstein [SIGGRAPH '98] Traditional cel animation Textured cel animation The process Input of the warp

7 Page 7 Marker curves Input of the warp model marker drawing marker Output of the warp A pair of marker curves P Q P Q At parameter t Many parameter values P Q P Q M(t) D(t)

8 Page 8 Output of the warp Controlling the warp Weights Viewing parameters Extra markers Viewing parameters Extra markers upright tilted without with Limitations Video

9 Page 9 Strengths Fits into current production pipeline Little effort per frame Avoids temporal artifacts Combines strengths of: 2-D: gestures, timing, anticipation 3-D: texture, occlusion, foreshortening Shadows for Cel Animation Lena Petrovic Brian Fujito Princeton University Lance Williams Disney Feature Animation Adam Finkelstein [SIGGRAPH '00] Motivation Motivation character character background scene background scene Motivation Shadow Mattes cast shadows (red) - shadows on background tone mattes (blue) - character shading contact shadows (green) - darkness underfoot no shadow shadow

10 Page 10 Project Goal Approach: 3D Models character 2D 3D background shadow mattes Process: Overview Background Construction Depth Specification Specifying Lights Rendering Compositing Process: Overview Background Construction Depth Specification Specifying Lights Rendering Compositing Process: Overview Background Construction Depth Specification Specifying Lights Rendering Compositing Process: Overview Background Construction Depth Specification Specifying Lights Rendering Compositing

11 Process: Overview Process: Overview Background Background Construction Construction Background Background Construction Construction Character Inflation Character Inflation Depth Depth Specification Specification Depth Depth Specification Specification Specifying Specifying Lights Lights Specifying Specifying Lights Lights Rendering Rendering Rendering Rendering Compositing Compositing Compositing Compositing Inflate -D shapes 33-D Inflate 3shapes using using Teddy Teddy [Igarashi [Igarashi 99] 99] Two caveats: perspective & layers character layer 3D model character layer 3D model Adding Adding aa second second layer layer character layers First First layer layer Adding Adding aa third third layer layer character layers 3D model Page 11 3D model

12 Obtaining Obtaining layers layers line art layers camera view 3D model Depth Specification Depth Specification shear Adjust Adjust depth depth while while preserving preserving silhouette silhouette translation off-angle view off off-angle shear camera view Compositing off-angle view off off-angle Video Tone Tone matte matte (blue) (blue) modifies modifies character character color. color. Other Other mattes mattes (red (red & & green) green) darken darken background. background. 33 frames Page frame frame cycle 16-frame frame cycle

13 Page 13 Limitations Manual creation of character layers No aesthetic controls for: shadow simplification shadow stylization Strengths Less human effort than hand-drawn drawn Plausible shadows even in complex scenes Lighting effects: animated lights, gobos Freedom to experiment with lights Conclusions Conclusions 3D methods may be used in 2D for: reducing human effort achieving new effects Lines between 3D and 2D are blurring Lines between 3D and 2D are blurring