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Paint By Numbers : Abstract Image Representation

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  1. Paint By Numbers : Abstract Image Representation Paul Haeberli Silicon Graphics Computer Systems ACM SIGGRAPH Computer graphics Proceeding of 17th, 1990

  2. Outline • Motivation • Overview • Painting Techniques • Stroke Attributes • Operations on Paintings • Advanced Techniques • Spice for Images • Conclusion • Further work

  3. Motivation

  4. 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.

  5. Overview

  6. Overview • Alternative to photorealism • Painterly rendering • Creation of artistic, stylized and abstract images • Impressionistic painting • Brush stroke control • User interactive system

  7. Painting Techniques

  8. Operation • Information from source image • Cursor across the canvas • Sampling color from image • Paint a brush stroke • Location • Color • Size • Direction • Shape

  9. Painting Example

  10. 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.

  11. 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.

  12. 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

  13. Stroke Shape • Shape • Significant influenceto final painting • Circle, rectangle, line,scattering of points,polygon, cone, user-defined shape

  14. Painting Example Diagonal stroke Pointillist representation

  15. Painting Example • • Cone shape brush • • Voronoi diagram polygon resterizing hardware• rendering of cones to construct 2D Voronoi diagrams of points Cone shape

  16. Operations on paintings

  17. 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

  18. Description Table

  19. Advanced Techniques

  20. Brush Direction • Brush direction using second image

  21. Edge drawing • Edge drawing using luminance gradient

  22. Texture mapping • Brush texture mapping

  23. Sampling Geometry • Sampling geometry using Ray-tracing

  24. Approximation • Approximation using Relaxation

  25. Spice for images

  26. Edge enhancement • “Pushing edge” • More explicit depth relationship • Using unsharp masking

  27. Color enhancement • Increase saturation • Lum = 0.3*R + 0.59*G + 0.11*B • Extrapolation

  28. 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

  29. Conclusion

  30. Conclusion • A system for producing abstract image • The first experiment on NPR • Making stylized abstract image • Interactive processing • Motivations for future works • Media • Method

  31. Advanced Work

  32. 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

  33. Digital analogues • Salisbury et al. 1994 • Pen and ink • Curtis et al. 1997 • Watercolor • Sousa et al. 1999 • Pencil drawing

  34. Automatic stroke • Litwinowicz, 1997 • Hertzmann, 1998 • Shiraishi and Yamaguchi, 2000 • Only global effect by user • Brush size or shape

  35. Stroke Dimension • Dana, 1996 • 8D dimension for social visualization[Dana] • To show social data Animation • Meier, 1996 • Using particle rendering methods