X-Toon: An Extended Toon Shader

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X-Toon An Extended Toon Shader

• Pascal Barla, Joelle ThollotARTIS GRAVIR/IMAGE
  INRIA
• Lee MarkosianUniversity of Michigan

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Outline

• Introduction
• Tone Detail
• Shape Detail
• Discussion and Future Work

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Introduction

• Toon shading simple but effective
• A dot product between a light vector and surface
  normal
• 1D texture
• dark to light regions
• 2 3 constant color (comics, traditional
  animation)
• Can be implemented efficiently via vertex and
  fragment programs on modern GPUs

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Limitation

• Does not reflect the importance or desired
  level of detail of a surface
• Depth-of-field
• View-independent
• View-dependent highlights,view-dependent
  backlighting effect
• Full accuracy
• A degree of abstraction so that small shape
  details are omitted

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X-Toon

• Supports view-dependent
• Tone detail
• Tone varies with depth or orientation relative to
  the camera
• 1D texture ? 2D texture
• Shape detail
• Using a modified normal field defined by
  interpolating between normal of the original
  shape and normal of a highly abstracted shape

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Outline

• Introduction
• Tone Detail
• Shape Detail
• Discussion and Future Work

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Tone Detail

• Toon texture 1D ? 2D
• Horizontal n?l (lambertian shading)
• Vertical tone detail
• This axis corresponds to its own 1D toon texture
• Attribute maps
• Control the tone detail and provide functions
• View-dependent attributes
• Depth-based attribute maps
• Orientation-based attribute maps
• ( LODs, aerial perspective, depth-of-field,
  backlighting, specular highlights)

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Outline

• Introduction
• Related Work
• Tone Detail
• Depth-based attribute mapping
• Orientation-based attribute mapping
• Shape Detail
• Discussion and Future Work

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Depth of A Point in 3D

• Distance between the eye and p
• Depth-of-field
• Distance along the focal axis
• LODs, Aerial perspective

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User-specified Parameters

• zmin
• the distance at which the detail starts
  decreasing
• r gt 1
• the scale factor that defines the coarsest detail
  at distance zmax rzmin

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Perspective Projection

• Formula for detail mapping

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Depth-of-Field

• Formula for detail mapping

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Depth-based LOD Effects
smooth out the shading with distance
mimic a discrete LOD behavior
make a receding shadow effect
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Focus-based Detail Map
blurred texture
a texture where contrast and opacity are decreased
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Aerial Perspective
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Outline

• Introduction
• Tone Detail
• Depth-based attribute mapping
• Orientation-based attribute mapping
• Shape Detail
• Discussion and Future Work

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Near-silhouette Attribute Mapping

• Attribute map based on the orientation of the
  surface with respect to the observer
• View-dependent effect
• Fading of near-silhouette regions, or brightening
  and coloring of near-silhouette regions to
  suggest a virtual backlight
• Near-silhouette attribute mapping

(controls the magnitude of the effect)
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Near-silhouette Abstraction Backlighting
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Specular Highlights

• View-dependent effect
• Model various material highlights
• Depending on the chosen 2D texture
• control the profile of the highlight (smoothness,
  width, alpha) so that it is correlated with the
  underlying tone
• e.g., plastics or metals
• Highlight attribute mapping (Phong highlight
  model)

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Highlights
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Outline

• Introduction
• Tone Detail
• Shape Detail
• Discussion and Future Work

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Abstracted Shape

• Geometric map
• Modify the surface normal field
• Map the input mesh to an abstracted shape
• lower bound for shape detail
• has a direct correspondence with the input
  surface
• Blending parameter
• Controls how the shader interpolates
• Important property
• Keeping the original silhouettes of the model

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Four Types of Abstracted Shape
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Outline

• Introduction
• Tone Detail
• Shape Detail
• Discussion and Future Work

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Performance

• Extensions to the original toon shader, aimed at
  retaining its simplicity while allowing more
  general behaviors

Model Size Resolution Toon X-Toon Ratio
Mech part 10,000 20,000 640x480 1280x950 287 268 241 222 1.19 1.21
David 26,051 49,998 640x480 1280x950 94 90 80 76 1.18 1.18
Terrain 105,152 208,962 640x480 1280x950 33 32 28 27 1.18 1.19
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Future Work

• Extend to handle other attributes
• Use optical flow to assign less detail to objects
  as they move faster in image space
• Multiple interpolation weights (geometric
  mapping)
• Haloing
• Labeled importance
• Points of interest

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Future Work

• Geometric mapping ? multiple shapes
• Control the shape of highlights

Tech. Rep. 2005 Multiscale Line Drawings from 3D
Meshes
IEEE Comput. Graph. 2003 Stylized Highlights for
Cartoon Rendering and Animation