Non-Photorealistic Rendering

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Non-PhotorealisticRendering
Greg Turk College of Computing and GVU Center
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Painterly Rendering for Animation Barbara Meier,
SIGGRAPH 1996
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Painterly Rendering Issues

• Frame-to-frame coherence (maintain strokes across
  time)
• Idea fix brush strokes in screen-space
• Problem shower door effect
• Better idea fix brush strokes to object

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Painting Pipeline
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Different Brushes and Orientation Fields
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Draw Image in Layers
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Video
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Pen and Ink Sketches
Mike Salisbury, Michael Wong, John Hughes and
David Salesin, SIGGRAPH 1997
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Pen and Ink

• Given grayscale image (e.g. photo)
• Make pen-and-ink illustration
• Approach

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Pen and Ink Sketches
Tone Map
Strokes
Orientation Field
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Pen and Ink Sketches
Tone Map
Strokes
Orientation Field
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Stroke Details

• Strokes are B-spline curves (similar to Bezier)
• Strokes clipped to silhouettes
• Stroke density controlled by blurred stroke image
• Strokes follow orientation field

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Painting Orientation Field
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Stroke Density
Strokes
Blurred Strokes
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Stroke Density Varies with Drawing Size
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Art-Based Rendering Of Fur, Grass
and Trees Kowalski, Markosian, Northrup,
Bourdev, Barzel and Hughes, SIGGRAPH 2000
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Approach

• Real-time rendering
• Use reference images for color and object ID
• Place strokes based on density
• Try to place same strokes on next frame

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Reference Images Hardware Rendering
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Final Image
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Stroke Drawing
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Illustrating Smooth Surfaces Aaron Hertzman and
Denis Zorin SIGGRAPH 2000
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Goals

• Create pen-and-ink strokes based on 3D geometry
• Show silhouettes
• Have cross-hatching

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Issues

• Silhouette detection
• Orientation field (use curvature)
• Hatching
• Undercuts

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Silhouette Detection
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Orientation Field Smoothing
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Orientation Field and Shading
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Hatching
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Hatching and Undercuts
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Results
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Results
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Other NPR

• Cel Animation
• Painterly Video
• Cel Video
• ???

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Painterly Video
What Dreams May Come
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Cel Animation Zelda Windwalker
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Cel-Like Video
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End