Exaggerated%20Shading%20for%20Depicting%20Shape%20and%20Detail

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Exaggerated Shading forDepicting Shape and Detail

• Szymon RusinkiewiczMichael BurnsDoug DeCarlo

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Motivation
Style of technical, medical, and topographic
illustrationsis designed to communicate surface
shape and detail
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Elements of Hand-Shaded Relief

• No shadows, no specular reflections
• Lighting from top (often top-left)
• Exaggeration of height
• Local adjustment of light
• Multiple scales

US National Park Service
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Goals

• Depicts detail at all surface orientations

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Goals

• Depicts detail at all surface orientations
• Locally resembles directional lighting
• Interpreted as shading, not texture
• Exploits lack of global consistency in visual
  system

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Exaggerated Shading

1. Increased local contrast
2. Adjustment of light direction
3. Multiscale computation

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1. Increased Local Contrast

• Lambertian

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Effects of Increased Local Contrast

• Brings out fine details
• Equalizes emphasis on different orientations

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Effects of Increased Local Contrast

• Brings out fine details
• Equalizes emphasis on different orientations

a 2
a 4
a 8
a 1
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2. Adjusting Light Direction

• Observation most detail under grazing light
• Therefore, vary light direction locally
• Per vertex, compute normal and smoothed normal
• Position light perpendicular to smoothed normal

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2. Adjusting Light Direction
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3. Multiscale Computation

• Scale of smoothing depends on scale of details
• Perform computation at several scales
• Collection of normals ni smoothed by increasing
  ?i
• Several shading passes, with pass i using ni and
  ni1
• Base coat using most-smoothed normals

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3. Multiscale Computation
Base coat
i 6
i 5
i 4
i 3
i 2
i 1
i 0
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Stylization OptionVarying Contribution of Each
Scale
ki ? ?i
ki const.
ki ? ?i-1
ki ? ?i -2
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Stylization Option Point of Interest

• User-selected point
• Downweighthigh frequenciesaway from that point
• Draws attentionto part of the modelCole et al.
  06

Uniform detail
With point of interest
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Stylization Option Colormap
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Algorithmic Option

• Light direction adjustment
• Instead of projecting light, find direction
  (perpendicular to smoothed normal)that maximizes
  local contrast
• Principal direction corresponding togreatest
  magnitude of normal curvature

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Principal Direction Adjustment
Projected light
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Principal Direction Adjustment
Using principal direction
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Principal Direction Adjustment
Projected light
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Principal Direction Adjustment
Using principal direction
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Principal Direction Adjustment
Projected light
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Principal Direction Adjustment
Using principal direction
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Applications

• Revealing surface texture

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Applications

• Visualizing quality of geometric processing

Approximating (Loop) subdivision
Interpolating (butterfly) subdivision
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Applications

• Volume rendering
• Standard nonrefractive transparency
• Exaggerated shading using multi-scale gradients

Cosine shading
Our method
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Demo
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Comparison
Cosine shading
Our method
Accessibility
Miller 1994
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Future Work

• What shape is perceived?
• Is perception consistent with actual shape?
• How much exaggeration is tolerated?

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Future Work

• What shape is perceived?
• Is perception consistent with actual shape?
• How much exaggeration is tolerated?
• Consistent with artistic technique?

Roy Lichtenstein
Exaggerated shading
Suggestive contours
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Future Work

• Other data types images, imagesnormals, etc.

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Summary

• Interactive technique for conveying shape and
  detail
• Increased local contrast
• Adjustment of light direction
• Multiscale computation

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Acknowledgments

• Thanks to the whole Princeton graphics group
• Models from Stanford, Georgia Tech, MERL,
  Viewpoint, Visible Human Project
• Funding from NSF (CCF-0347427) and the Sloan
  Foundation

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Source Code

• http//xshade.cs.princeton.edu/