NPR

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NPR Vis

• Non-Photorealistic Rendering
• Caricature
• Shape/Volume Visualization

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Different Objectives

• Realistic More correct
• Artistic More interesting
• Scientific More informative

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Terminology

• Visualization
• Interpret geometry/data/information in visual
  form (metaphor)
• Volume visualization
• Rendering a 3D scalar or vector field
• Rendering
• Mechanics of computing pixel colors from a
  graphic model
• Photorealism
• Attempt to reproduce physics of light
• Non-Photorealistic Rendering (NPR)
• Stylistic rendering effects
• Caricature
• Extract exaggerate distinguishing features

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Edge Attributes

• Sharp edges (creases)
• Surface normal discontinuities
• Where surfaces meet
• Tessellation edges are smooth
• Silhouettes
• Separate front and back facing parts
• Form closed loops
• Visible
• Bounding at least one front faces
• Not occluded from the viewpoint

Which edges are shown?
Which are dashed?
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Technical Illustration

• Silhouettes
• Hidden Parts
• Color cues
• Hatching
• Cross-sections
• Interferences

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Amy Gooch - Bruce Gooch - Peter Shirley - Elaine
Cohen

• http//www.cs.utah.edu/gooch/SIG98/abstract.html
• Use hue shift to enhance orientation
• Warmer tones perceived as closer
• Mix with mid part of luminance

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Art Imitation

• Hatching
• Painting
• Toons

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Antonio Haro (class project)

• Approach
• Find the (visible) silhouette edges
• Parameterize them
• Offset along tangent normal
• Draw using 'sketched' style

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How to find the silhouettes?

• Edges that separate front and back faces

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WYSIWYG NPRDrawing Strokes Directly on 3D Models
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NPR Simulating Various Media
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Long-Range Goal
Create full scene by drawing
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NPR Dynamic Imagery
Painterly rendering for video Litwinowicz 97
Painterly rendering for3D models Meier 96
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NPR Interactive Rendering
Kowalski 99
Praun 01
Gooch 98
Algorithms for aesthetic qualities.
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WYSIWYG NPR
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Stylistic Flexibility
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Overview of Components
Base Coat Brush Style Paper Effect Decals Outlines
Hatching
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Overview of Components
Base Coat Brush Style Paper Effect Decals Outlines
Hatching
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Decal Strokes

• Direct control
• Draw on surface
• For magnified or oblique views
• No blurring
• Explicit control of stroke width
• unlike texture maps

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Overview of Components
Base Coat Brush Style Paper Effect Decals Outlines
Hatching
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Outlines
Artist sketches over outlines
Stylization retainedfor novel views

• Two types of outlines
• Creases
• Silhouettes

creases
silhouettes
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Silhouette Stylization

• Silhouettes are view-dependent.
• Problem 1 localized stylization?!?
• Solution rubber-stamp globally

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Silhouette Parameterization
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Silhouette Tracking

• Silhouettes are view-dependent.
• Problem 2 parameterization coherence
• Solution screen-space tracking

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Robert Kalnins, Philip Davidson, Lee Markosian,
?Adam Finkelstein

• http//www.cs.princeton.edu/gfx/pubs/Kalnins_2003_
  CSS/index.php
• Coherent Stylized Silhouettes
• Silhouettes correspondence
• in consecutive frames
• Track silhouettes in 3D

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Overview of Components
Base Coat Brush Style Paper Effect Decals Outlines
Hatching
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Hatching Level of Detail

• Free hatching
• User-defined LOD
• Structured hatching
• Automatic LOD

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Structured Hatching LOD
LOD based on size of group
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Hatching Lighting Scheme

• Fixed Hatching
• Light fixed in world frame

• Mobile Hatching
• Light moves with camera

fixed
mobile
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Mobile Hatching Lighting Model
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Future Work

• Adopt style synthesis more broadly
• Object interactions (e.g. shadows)

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Base Coat

• Per object
• Shaders (e.g. Toon)
• Lighting Model
• Paper Texture
• etc.

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Brush Style

• Per stroke
• Color
• Width profile
• Alpha profile
• Paper
• etc.
• Rendered as triangle strips.

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Strokes
Visibility computed via ID reference image.
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Paper Effect

• Height field texture
• Peaks catch pigment
• Valleys resist pigment

• Implementation
• Pixel shader

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Further Reading

• Craig Raynolds (Online survey)
• http//www.red3d.com/cwr/npr/
• Fredo Durand (Paper)
• An invitation to discuss Computer Depiction

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3D Caricatures
Ergun Akleman Jon Reisch
Visualization Sciences Program College of
Architecture Texas AM University
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Abstraction
By Sebastian Kruger
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Simplification
By Hanoch Piven
By David Cowles
King Louis Philippe by Charles Philipon
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Attempts on Automated Caricature
Susan Brennan Caricature Generator 1982 M.
Tominaga, S. Fukuoka, K. Murakami and H.
Koshimizu, Picasso System, 1997 S. Iwashita, Y.
Takeda and T. Onisawa , Expressive Facial
Caricature Drawing, 1999 J. Nishino, T. Kamyama,
H. Shira, T. Odaka and H. Ogura, Facial
Caricature Drawing System, 1999 Lin Liang, Hong
Chen, Ying-Qing Xu, Heung Shum, Example Based
Caricature, 2003
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A New Morphing Approach to create Extreme
Caricatures Ergun Akleman with James Palmer
Ryan Logan (Visual 2000)
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3D caricatures by students
By Han Lei
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Case Study Julia Roberts - 1. Data Collection
By Jan Op De Beeck
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2. Unique Feature Identification
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3. Abstract 3D shape creation
Reclining Bather, by Pablo Picasso, 1931 Musee
Picasso, Paris
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4. Skin Modeling
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4. Final Rendering
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Illustration vs. Volume Rendering
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Biology
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Medicine
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GIS
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Chemistry
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Weather
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Simulation
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Flow
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Mechanical
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Terrain visualization Victoria Interrante

• http//www-users.cs.umn.edu/interran/texture/inde
  x.html
• Draw lines of principal curvature

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Hidden surfaces Victoria Interrante

• http//www-users.cs.umn.edu/interran/3Dshape.html
  
• Use principal curvature lines to distribute
  points on transparent iso-surfaces

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Volume-Visualization

• Density
• Section
• Isosurface
• Vector field
• Flow

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Traditional Medical Image
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Where Is Visualization Today?

• Realistic visualization in real-time is close

Images courtesy of Joe Kniss
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Perceptualization David Ebert

• David S.Ebert
• Electrical Computer Engineering
• Purdue University
• ebertd_at_purdue.edu

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Advanced Real-time Visualization Examples
Images from Kniss, Premoze, Hansen, Ebert,
Interactive Translucent Volume Rendering and
Procedural Modeling, IEEE Visualization 2002.
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Interactive Volume Illustration and Stippling
Lu, Morris, Ebert, Hansen, Rheingan,
Non-photorealistic Volume Rendering Using
Stippling Techniques, IEEE Visualization 2002.
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The Data Deluge

• Example 2 scientific visualization of
  Osprey-like aircraft
• 7.4 million tetrahedra in simulation
• 1362 timesteps
• Multiple data values per grid point (velocity,
  vorticity, etc.)
• Very long simulation andvisualization time on
  largemachines

Visualization courtesy of Mississippi State
Engineering Research Center
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The Data Deluge

• Example 3 scientific visualization of turbulent
  mixing
• 8 billion voxels per timestep
• 274 timesteps
• Terabytes of data

Visualization courtesy of Mark Duchaineau, Peter
Lindstrom, et al., Lawrence Livermore National
Labs
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Selective Enhancement Techniques

• Most medical and technical illustration uses
  selective detail to focus the viewers attention