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Paint By Numbers : Abstract Image Representation Paul Haeberli Silicon Graphics Computer Systems ACM SIGGRAPH Computer graphics Proceeding of 17 th , 1990 Outline Motivation Overview Painting Techniques Stroke Attributes Operations on Paintings Advanced Techniques Spice for Images

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Paint By Numbers : Abstract Image Representation

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Paint by numbers abstract image representation l.jpg

Paint By Numbers : Abstract Image Representation

Paul Haeberli

Silicon Graphics Computer Systems

ACM SIGGRAPH Computer graphics

Proceeding of 17th, 1990


Outline l.jpg

Outline

  • Motivation

  • Overview

  • Painting Techniques

  • Stroke Attributes

  • Operations on Paintings

  • Advanced Techniques

  • Spice for Images

  • Conclusion

  • Further work


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Motivation


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Motivation

  • Producing images indistinguishable from photograph

  • Graphic designer’s choice

    • Photorealistic, Not always the best choice

    • “How much use is a photograph to mechanics when they already have the real thing on front of them?”[Lansdown and Schofield]

    • Visual effect intended by designer

      [Lansdown and Schofield] J.Lansdown and S.Schofield. Expressive rendering: A review of nonphotorealistic techniques. IEEE ComputerGraphics and Applications, 1995.


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Overview


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Overview

  • Alternative to photorealism

  • Painterly rendering

  • Creation of artistic, stylized and abstract images

    • Impressionistic painting

  • Brush stroke control

  • User interactive system


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Painting Techniques


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Operation

  • Information from source image

    • Cursor across the canvas

    • Sampling color from image

  • Paint a brush stroke

    • Location

    • Color

    • Size

    • Direction

    • Shape


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Painting Example


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Stroke Location

  • Stochastic distribution around cursor

  • Example of interactive particle system[Reeves]

    [Reeves] William T. Reeves and Ricki Blau, “Approximate and probabilistic algorithm for shading and rendering structured particle systems”, Computer Graphics, 1985.


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Stroke Color

  • RGB and alpha value

  • Time limitation to pick new color

    • “put-that-color-there” procedure[Lewis]

    • Restrict to small number of color

      [Lewis] John-Peter Lewis, “Texture Synthesis for Digital Painting”, Computer Graphics, 1984.


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Stroke Size and Orientation

  • Size

    • Control by cursor speed

      • Easy to create rough representation

    • Control by arrow keys

  • Orientation

    • Direction of cursor

    • Mouse gesture

    • Image gradient


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Stroke Shape

  • Shape

    • Significant influenceto final painting

    • Circle, rectangle, line,scattering of points,polygon, cone, user-defined shape


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Painting Example

Diagonal stroke

Pointillist representation


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Painting Example

  • • Cone shape brush

    • • Voronoi diagram polygon resterizing hardware• rendering of cones to construct 2D Voronoi diagrams of points

Cone shape


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Operations on paintings


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Painting Description

  • Painting as an ordered set of strokes

  • Containing stroke information

  • Operations on paintings

    • Transform painting into RGB images

    • Unary operation – scaling, sorting, adding noise, etc.

    • Binary operation – interpolation, extrapolation, animation, etc


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Description Table


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Advanced Techniques


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Brush Direction

  • Brush direction using second image


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Edge drawing

  • Edge drawing using luminance gradient


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Texture mapping

  • Brush texture mapping


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Sampling Geometry

  • Sampling geometry using Ray-tracing


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Approximation

  • Approximation using Relaxation


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Spice for images


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Edge enhancement

  • “Pushing edge”

  • More explicit depth relationship

  • Using unsharp masking


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Color enhancement

  • Increase saturation

  • Lum = 0.3*R + 0.59*G + 0.11*B

  • Extrapolation


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Color restriction and Background Color

  • Color restriction

    • Limited color for overall harmony and unity

    • Color quantization of source image

    • Noise for no contouring

  • Background cover

    • Unity and integrity

    • Color perception


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Conclusion


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Conclusion

  • A system for producing abstract image

    • The first experiment on NPR

    • Making stylized abstract image

    • Interactive processing

    • Motivations for future works

      • Media

      • Method


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Advanced Work


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Inspiration

  • Haeberli’s work

    • The first work on NPR

    • Some issues

      • Stroke methods, attributes, animation, etc

  • After Haeberli’s work

    • Considerable works on painting system

    • Two large categorization

      • Digital analogues

      • Automatic stroke


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Digital analogues

  • Salisbury et al. 1994

    • Pen and ink

  • Curtis et al. 1997

    • Watercolor

  • Sousa et al. 1999

    • Pencil drawing


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Automatic stroke

  • Litwinowicz, 1997

  • Hertzmann, 1998

  • Shiraishi and Yamaguchi, 2000

  • Only global effect by user

    • Brush size or shape


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Stroke Dimension

  • Dana, 1996

    • 8D dimension for social visualization[Dana]

    • To show social data

Animation

  • Meier, 1996

    • Using particle rendering methods


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