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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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NPR - 2D to 3D, painting and rendering

Daniel Teece

Walt Disney Feature Animation

daniel.teece@disney.com


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Introduction

Coming up…

  • Background

  • 2D and 3D brush models

  • Animation problems and approaches

  • Examples of NPR used in film production

  • Sable


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NPR Characteristics

What defines an NPR system?

  • “Natural Media Emulation”

  • 2D / 3D

  • Interactivity / Artistic direction

  • Brushes, strokes and marks

  • Complications - visibility … animation!


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NPR Cross-section

2D

3D

automatic

stroke renderers

image processors

2D paint systems

3D paint / renderers

interactive


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NPR Cross-section

2D

3D

automatic

Litwinowicz97

Hertzmann00

Hertzmann98

Meier96

Haeberli90

DeepCanvas

Teece98

Kalnins02

interactive


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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]


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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


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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


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Brush Models - 3D

Strokes and Surfaces

  • Pixel (texture maps)

  • Geometry (points & matrices)

  • Procedure (paths & width vectors)

    From [Katanics,Lappas99]


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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


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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


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3D Expressive Paint

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


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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)


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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


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DeepCanvas

From [Katanics,Lappas99]

A 2D/3D painting and rendering system


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DeepCanvas

From [Katanics,Lappas99]

Simplified stroke representation -

stroke spine and width vectors


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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


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Sable

Requirements:

  • Match look of original artwork (stylized, flat, few strokes, black background)

  • Retain performance seen in pencil animation

  • Animate strokes smoothly & efficiently


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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


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Sable

© Disney

Animated non-mapped DeepCanvas strokes


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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


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Sable

© Disney


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Sable

Animation

Rigged curve set animated to match traditional animation

© Disney


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Sable

Results

© Disney


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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


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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


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Acknowledgements

  • Mike Gabriel

  • George Katanics

  • Jack Brooks


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