1. Computer Graphics& 3D Painting Xia Jiazhi Central South University

2. Xia Jiazhi • Lecturer at Central South University • Received Ph.D. at Nanyang Technological University, Singapore, in 2011 • Research: Computer Graphics and Human-Computer Interaction

3. What is Computer Graphics?

4. What is Computer Graphics • A technique to generate digital images from 3D models using computer.

5. Which one is the real BMW?

6. Is it Fake or Photo?

7. The image may cheat us

8. Why Computer Graphics?

9. Why computer graphics • About 50% of the brain neurons are associated with vision. • Dominant form of computer output. • Enable scientists (also engineers, doctors, and general users) to observe their simulation and computation. • Computer graphics is application driven! • Movie • Game • Computer-aided design (CAD) • Medical imaging • Computer art • Graphical user interface (GUI) • Scientific visualization

10. Movies • If you can imagine it, it can be done with computer graphics. • More than one billion dollars on special effects. More and more of these images exist only within the memory of a computer. No end in sight for this trend! • Computer graphics is now as much a part of the video and movie production industry as stuntmen and makeup.

11. Video Games • Games are the driving force in computer graphics. • Games market is the stimulus for the powerful graphics processors (GPU) Crysis 3 2013 Spacewar 1961 Counter Strike 2005

12. Computer-Aided Design(CAD) • Today, most mechanical and electronic designs are executed entirely on computer. Increasingly, architectural and product designs are also migrating to the computer. Automated tools are also available that verify tolerances and design constraintsdirectly from CAD designs. • CAD can significantly reduce the design cycles for industrial products, e.g., the mobile phones

13. Graphical User Interface(GUI)

14. Visualization

15. How Computer Graphics Works?

16. Simulating the Everyday World • Three broad areas: • Modeling(Geometric) = Shape • Animation = Motion/Behavior • Rendering = Appearance

17. Representing the Shape

18. Geometric Modeling

19. Geometric Modeling

20. Geometric Modeling

21. Animating the world

22. Animation

23. Natural phenomena simulation

24. Rendering

25. Rendering • Rendering is the process of generate an image from a scene, which contains geometry, viewpoint, texture and lighting information. It is similar to photography or cinematography. • Simulation of realistic lighting, shadows, atmosphere, color, texture and optical effects such as refraction of light or motion-blur seen on moving objects.

26. Representing the Surface Details

29. Texture Maps • How is texture mapped to the surface? • Dimensionality: 1D, 2D, 3D • Texture coordinates (s, t) • Surface parameters (u, v) • How to assign the Surface parameters? • Parameterization!

30. 3D Painting • Assign colors to vertices directly in a painting interface • WYSIWYG(What You See Is What You Get) system • Painting on self-occluded model • A lot of manual work, even impossible

31. Start from Reality Model From Jeremy Birn

32. Start from Reality model From Jeremy Birn Model + illumination

33. Start from Reality Model From Jeremy Birn Model + illumination Model + illumination + Texture

34. 3D Painting • An interactive technique for 3D model surface properties editing • 3D model surface properties are required by reconstructing the surface details of the real object • Color • Illumination • Transparency • Normal（bump mapping） • Displacement mapping • ……

35. The 3D Painting System

36. The Challenge of 3D Painting • The dimension • 3D interaction + 3D display • 2D interaction interface is still the major method of industry[P. Hanrahan et al. 1990] • Operation • The occlusion is a challenge to interaction even in real world • The Creation skill • General users lack the professional creation skill

37. 1. Occlusion

38. Our Method

39. Depth Layer Layer 1 Layer 2

40. Depth peeling Layer 1 Layer 2

41. Region Segmentation Depth Information The pixel adjacent information Region Segmentation Region adjacent information

42. Layer-aware Interaction

43. Layer-aware Interaction

44. A complete painting demo

45. 2. The difficulty of creation • 3D painting requires professional creation skill

46. Decal System • Copy+Paste Schmidt et al. 2006

47. Exponential Map Can only control the center point and the direction

48. Sketch-based texture mapping • Free control of the texture deformation • More close to painting experience of general users

49. Sketch-based texture mapping Extended exponential map Texture map

50. Extended exponential map