Photorealism: Ray Tracing Huamin Wang (whmin@cc.gatech) Georgia Tech Nov 11, 2008

1. Photorealism: Ray Tracing Huamin Wang (whmin@cc.gatech.edu) Georgia Tech Nov 11, 2008

2. Quiz 1

3. Quiz 2 Henrik Wann Jensen, 1992

4. quiz "Boreal" by Norbert Kern (2004)

5. "Christmas Baubles" by Jaime Vives Piqueres (2005)

6. quiz "The Wet Bird" by Gilles Tran (2001)

7. CONTENT • Basics of ray tracing • Monte Carlo integration • Distributed ray tracing • Soft shadow • Glossy surface • Fuzzy glass • Depth of field • Motion blur • Conclusion

8. Basics of ray tracing Light 0 Camera E Image Plane L(E)? Object 1 Object 0 Light 1

9. Light Transport N I L(I) E L(E) p Object

10. Phong modelAn example of Reflectance N I L(I) E R L(E) p

11. Light Transport N E L(E) p

12. Light Transport in Basic Ray Tracing L(I1) N L(In) I L(R) E L(E)? R T L(T) known direct illumination Glass (indirect) Mirror (indirect)

13. Basics of ray tracing g(p,I0)=1 Light 0 I0 Camera R N Image Plane • L(E) • p=Intersection(E); • if p==NULL return backgrd; • R=Reflection(E, N); • T=Refraction(E, N); • return l; E p I1 T Object 1 Object 0 Light 1 g(p,I1)=0

14. Result of Basic Ray Tracing Huamin Wang et al, 2005

17. …area of a triangle… P1=(P1.x, P1.y, P1.z) P3=(P3.x, P3.y, P3.z) P2=(P2.x, P2.y, P2.z)

18. Ray-Implicit Surface Intersection Implicit Surface: f(P)=0 Ray:P=O+tD Solution t: f(O+tD)=0 r Example (Sphere): C

19. Review: Basics of ray tracing Camera E L Intersection L T R L Intersection Intersection L L T R R L Intersection Intersection Intersection L

20. Result of Basic Ray Tracing A rendering result: max_depth=16

21. Limitations of Basic Ray Tracing R N Image Plane E p • Light Source • Indirect Illumination • Lens Camera • Pixel Intergration • …. T Object 1 Object 0 Light 1

22. CONTENT • Basics of ray tracing • Monte Carlo integration • Distributed ray tracing • Soft shadow • Glossy surface • Fuzzy glass • Depth of field • Motion blur • Conclusion

23. Monte Carlo Integration • What’s the integral of ? a b

24. Monte Carlo Integration • What’s the integral of ? Ω

25. Monte Carlo Integration • What’s the integral of ? Ω

26. Monte Carlo Integration • Given a 1D uniform random function Rand() from 0 to 1, How to uniformly sample a rectangle? (a,b) dy dx dy dx b p=(x,y) dy dx a (0,0)

27. Monte Carlo Integration • Given a 1D uniform random function Rand() from 0 to 1, How to uniformly sample a sphere? WRONG!

28. http://www.cs.utah.edu/~thiago/cs7650/hw5/ Monte Carlo Integration • Given a 1D uniform random function Rand() from 0 to 1, How to uniformly sample a sphere?

29. Monte Carlo Integration • Given a 1D uniform random function Rand() from 0 to 1, How to uniformly sample a sphere?

30. http://www.cs.utah.edu/~thiago/cs7650/hw5/ Monte Carlo Integration • Given a 1D uniform random function Rand() from 0 to 1, How to uniformly sample a sphere?

31. Monte Carlo Integration • Given a 1D uniform random function Rand() from 0 to 1, How to uniformly sample a region? (a,b) Rejection Method While(1) { if ( (x,y) in Ω ) break; } p=(x,y) (0,0)

32. Monte Carlo VS Riemann • Similar: • The difference between MC and Riemann:

33. Monte Carlo VS Riemann • The advantage of Monte Carlo

34. CONTENT • Basics of ray tracing • Monte Carlo integration • Distributed ray tracing • 1. Soft shadow • 2. Glossy surface • 3. Fuzzy glass • 4. Depth of field • 5. Motion blur • Conclusion

35. 1. Hard Shadow by Point Light N E L(E) p Object Illuminated: Shadow: Genetti & Gordon, 1993

36. 1. Soft Shadow by Area Light 1. No Shadow 2. Half Shadow (penumbra) 3. Complete Shadow (umbra) N E L(E) Object Genetti & Gordon, 1993

37. 1. Area Light, distributed ray tracing N N I L(I) E E L(E) L(E) p p Object Object • For i=1:N • Ii=Uniform_Sample(Ω); • End;

38. 1. Mathematical Validation I E: Eye Ω : Light p

39. http://www.cs.utah.edu/~thiago/cs7650/hw5/ 1. An Area Light Example Cornell Box: 4 samples

40. http://www.cs.utah.edu/~thiago/cs7650/hw5/ 1. An Area Light Example Cornell Box: 10 samples

41. http://www.cs.utah.edu/~thiago/cs7650/hw5/ 1. An Area Light Example Cornell Box: 100 samples

42. Distributed Ray Tracing • It was proposed by Cook, Porter and Carpenter in 1984. • It is NOTray tracing on a distributed system. • It is a ray tracing method based on sampling rays randomly with certain distribution.

43. 2. Glossy Surface Definition L(R) L(E) L(E) R E R E

44. 2. Glossy Surface, Distributed Ray Tracing L(E) R E • For i=1:N • Ri=Uniform_Sample(Ω); • End; Mirror 16 samples 4 samples 64 samples http://www.cse.ohio-state.edu/~xue/courses/782/final/dtr.html

45. 2. Fuzzy Glass, Distributed Ray Tracing L(E) E T • For i=1:N • Ti=Uniform_Sample(Ω); • End; Mirror 4 samples 16 samples http://www.cse.ohio-state.edu/~xue/courses/782/final/dtr.html

46. 3. An Fuzzy Glass Example Different glasses rendered by distributing refracted rays, from left to right: ideal glass, fuzzy glass, more fuzzy glass.

47. 4. The Pinhole Camera Model Camera Image Plane E The projection model in basic ray tracing Object Pinhole Pixel Pixel Object Image Plane The pinhole camera model

48. 4. Depth of Field: in-focus In-focus: lens Pixel Pixel Image Plane Focal plane

49. 4. Depth of Field: out-of-focus Out-of-focus: Circle of Confusion lens Pixel object Image focal

50. 4. Depth of Field: out-of-focus Out-of-focus: Circle of Confusion lens Pixel object Image focal