1. computer graphics & visualization NPR – Non-photorealistic rendering

2. computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group NP vs. NPR?

3. computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group PR vs. NPR

4. computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Why NPR? “Science”: Convey information more efficiently by reduction, abstraction, accentuation “Art”: create novel artistic, creative imagery

5. computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Reasons against photorealism? Too much (unnecessary) information  maps, technical/medical illustrations Constraints Creativity  improper for caricatures, comics, art Time consuming image generation  (probably) not feasible for real-time applications No room for the fantasy of the viewer „Photorealism, like pornography, leaves nothing to the imagination“ - Cassidy Curtis

6. computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Applications Art

7. computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Applications Comics/ Cartoons

8. computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Applications Architecture

9. computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Applications Maps

10. computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Applications Maps

11. computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Applications Medicine

12. computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Applications Medicine

13. computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Applications Technical Illustrations

14. computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Applications Archeology

15. computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Basics Object Space Screen Space 3D 2D Geometry processing Image processing Object PrecisionScreen Precision Pseudo code: „for each Object do…“ Pseudo code: „for each Pixel do…“ Usually does not require recomputation on affine transformations Recomputation every time the image changes (  no frame-to-frame coherence „Shower Door Effect“)

16. computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Algorithms Toon/Cell ShadingSketchingHalftoningScreeningStippling

17. computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Toon Shading Toon/Cell Shading: Rendering technique to create cartoon like movies

18. computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Toon Shading -large homogenous regions -very few colors -enhanced silhouettes -simple geometry -reduction to important elements Motivation: Simpel and (semi-) automatic (mass-) production of comics

19. computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Toon Shading Color computation (object space): precompute 2-3 shades for each color (Light-/ Shadow- color) and store them in a 1D texture assignment of final color by 1D texture lookup 1D texture surface

20. computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Toon Shading Silhouettes (Screen Space) generate Depth map generate Depth map find discontinuities find discontinuities generate normal map generate normal map find discontinuities find discontinuities

21. computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Toon Shading Combination of both silhouette detections ideas: Technical Illustrations :

22. computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Sketching Sketching: Automatic method to create computer images that look like and hand-made drawings

23. computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Computer Sketching Motivation: Ideal to present concepts (architecture) Precise Depiction often looks very sterile Methods: Use special output device Image space post-processing Object space 3D model modification

24. computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Computer Sketching Example: Object space approach: Pseudo-Randomly change length of lines Cut lines into multiple sub-lines Move line center

25. computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Halftoning Halftoning: Reproduce (color/grayscale) images with a (very) limited amount of colors, usually only black/white “Historically”, a necessity to print images in newspapers

26. computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Halftoning Algorithm: Input: Gray scale image Group pixles (  loss of image resolution) Compute average intensity Replace group by dither matrix294618 735

27. computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Halftoning limited resolution of the human visual system

28. computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Error Diffusion Floyd and Steinberg

29. computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Screening Bild Screening: Artistic variation of the halftoning algorithm Replaces the simple dither matrix by one ore more complex images

30. computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Screening Screening with text

31. computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Stippling Stippling: Construct an image of a large number of dots

32. computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Pointillismus Georges Seurat - Ein Sonntagnachmittag auf der Insel La Grande Jatte

33. computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Stippling Motivation: Results in very “clean/cold” illustrations Very time-consuming to create manually Applications: Scientific and technical illustrations Art Print media

34. computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Stippling Stipple points simulate both tone and texture. Usually a uniform distribution without any recognizable pattern is used

35. computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Stippling Object space: prioritized line textures

36. computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Stippling Other prioritized line textures

37. computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Stippling

38. computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Object / Image Space Stippling

39. computer graphics & visualization Image Synthesis – WS 07/08 Dr. Jens Krüger – Computer Graphics and Visualization Group Object / Image Space Stippling black-and-white stippling Supersampling in screen space surface based anti-aliasing