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Painters interface uses Digpaint (in-house 2D paint system) BG Painters use a set of reference layers prepared by TD (grey render, outlines ...

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Presentation Transcript
slide2

NPR - 2D to 3D, painting and rendering

Daniel Teece

Walt Disney Feature Animation

[email protected]

slide3

Introduction

Coming up…

  • Background
  • 2D and 3D brush models
  • Animation problems and approaches
  • Examples of NPR used in film production
  • Sable
slide4

NPR Characteristics

What defines an NPR system?

  • “Natural Media Emulation”
  • 2D / 3D
  • Interactivity / Artistic direction
  • Brushes, strokes and marks
  • Complications - visibility … animation!
slide5

NPR Cross-section

2D

3D

automatic

stroke renderers

image processors

2D paint systems

3D paint / renderers

interactive

slide6

NPR Cross-section

2D

3D

automatic

Litwinowicz97

Hertzmann00

Hertzmann98

Meier96

Haeberli90

DeepCanvas

Teece98

Kalnins02

interactive

slide7

2D Strokes

2D paint strokes and reference images

  • Images in, images out
  • Stamp-based, procedural or physically-based
  • Haeberli’s “Paint by Numbers” [Haeberli90]
  • Hertzmann’s subsequent improvements [Hertzmann98]
slide8

Animating Strokes

Finding frame to frame coherence

  • Stroke placement methods cause temporal artifacts
  • Locking strokes to canvas improves coherence but can look strange
  • Strokes should move smoothly, matching motion of subject
slide9

Image Space Stroke Animation

Optical flow techniques

  • “Processing images and video for an impressionist effect” [Litwinowicz97]
  • “Painterly rendering for video and interaction” [Hertzmann00]
  • Strokes moved, added or removed based on frame-to-frame optical flow data
  • Strokes retain two-dimensional nature
slide10

Brush Models - 3D

Strokes and Surfaces

  • Pixel (texture maps)
  • Geometry (points & matrices)
  • Procedure (paths & width vectors)

From [Katanics,Lappas99]

slide11

Painterly Rendering for Animation [Meier96]

A 3D stroke renderer

  • Particles placed on geometry, based on surface area
  • Strokes placed at particle positions, with parameters driven by reference renders
  • Depth sorting and layering for visibility
  • Smooth stroke animation, with a painterly appearance
slide12

3D Expressive Paint

A 3D interactive painting system

  • Strokes and marks in object space
  • Developed for animating painterly imagery
  • Fully interactive
  • Two types of stroke - 3D geometry and screen aligned
slide13

3D Expressive Paint

3D Strokes are painted interactively by ray-casting in to the stencil scene

slide14

3D Expressive Paint

  • Paint order / depth order (“clump buffer”)
  • Silhouettes - coherence & character [Kalnins02]
  • Brush model - lighting, textures etc.
  • Limited animation support (e.g. deforming surfaces)
  • Border or transition strokes between surfaces (back to 2D/3D relationship)
slide15

DeepCanvas

A 3D painting and rendering system

  • Painters interface uses Digpaint (in-house 2D paint system)
  • BG Painters use a set of reference layers prepared by TD (grey render, outlines …)
  • Strokes are stored in stroke script files, and mapped on to 3D geometry
  • Renderer ‘re-paints’ scene from new angle
slide16

DeepCanvas

From [Katanics,Lappas99]

A 2D/3D painting and rendering system

slide17

DeepCanvas

From [Katanics,Lappas99]

Simplified stroke representation -

stroke spine and width vectors

slide18

Sable

A 2D/3D stroke renderer

  • Library of specifically scanned & processed strokes
  • Operates as a pipeline component with Inka
  • Stroke paths can be any Inka line type
  • Workflow designed to be driven by traditional animation
slide19

Sable

Requirements:

  • Match look of original artwork (stylized, flat, few strokes, black background)
  • Retain performance seen in pencil animation
  • Animate strokes smoothly & efficiently
slide20

Sable

First attempt - DeepCanvas brush

  • Utility to convert ink lines to stroke scripts
  • All pre-written software (except converter)
  • Problems achieving distinctive look
  • DeepCanvas procedural brush sensitive to segment distribution
slide21

Sable

© Disney

Animated non-mapped DeepCanvas strokes

slide22

Sable

Brush model

  • Texture-based, extracted from example set
  • Library of textures and shapes
  • Stroke geometry is grown along spine curve
  • Sharp twists are problematic … splitting
slide23

Sable

© Disney

slide24

Sable

Animation

Rigged curve set animated to match traditional animation

© Disney

slide25

Sable

Results

© Disney

slide26

Sable

Summary

  • Animate strokes smoothly & efficiently
  • Able to match appearance of strokes
  • Integration with other tools in pipeline
  • Animators able to work with a pencil
slide27

Conclusions

  • Combining animation and NPR can be approached with 2D or 3D methods
  • With 2D, frame-to-frame coherence can be difficult to maintain
  • With 3D, some operations may detract from the painterly look
  • Brush models vary, but are important
  • Interaction and workflow are also important
slide28

Acknowledgements

  • Mike Gabriel
  • George Katanics
  • Jack Brooks
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