1. 1 CSCE 441: Computer Graphics Lighting Jinxiang Chai

2. Scan conversion 3D Rendering pipeline Modeling transformation lighting Viewing transformation Project transformation Clipping Image Transform into 3D world system Illuminate according to lighting and reflectance Transform into 3D camera coordinate system Transform into 2D camera system Clip primitives outside camera’s view Draw pixels (includes texturing, hidden surface, etc.)

3. Scan conversion 3D Rendering pipeline Modeling transformation lighting Viewing transformation Project transformation Clipping Image Transform into 3D world system Illuminate according to lighting and reflectance Transform into 3D camera coordinate system Transform into 2D camera system Clip primitives outside camera’s view Draw pixels (includes texturing, hidden surface, etc.)

4. Outline Ambient, diffuse and specular light Light attenuation & spot lights Readings: HB 17-1,12- 2,17-3

5. Lighting/Illumination Color is a function of how light reflects from surfaces to the eye Global illumination accounts for light from all sources as it is transmitted throughout the environment Local illumination only accounts for light that directly hits a surface and is transmitted to the eye

6. Direct and Indirect Light

7. Global Illumination II

9. Lighting/Illumination Color is a function of how light reflects from surfaces to the eye Global illumination accounts for light from all sources as it is transmitted throughout the environment Local illumination only accounts for light that directly hits a surface and is transmitted to the eye

10. Light Sources Any object emitting radiant energy is a light source that contributes to the lighting effects for other objects in a scene Point light sources: defined by its position and the color of the mitted light (RGB) Infinitely distant light sources: basically a point light source very far from a scene. Defined by its direction and the color of the light (RGB)

11. Reflection Models Definition: Reflection is the process by which light incident on a surface interacts with the surface such that it leaves on the incident side without change in frequency.

12. Reflection Models Definition: Reflection is the process by which light incident on a surface interacts with the surface such that it leaves on the incident side without change in frequency.

13. Reflection Models Definition: Reflection is the process by which light incident on a surface interacts with the surface such that it leaves on the incident side without change in frequency.

14. Reflection Models Definition: Reflection is the process by which light incident on a surface interacts with the surface such that it leaves on the incident side without change in frequency.

15. Reflection Models Definition: Reflection is the process by which light incident on a surface interacts with the surface such that it leaves on the incident side without change in frequency. Reflected light?

16. Reflection Models Definition: Reflection is the process by which light incident on a surface interacts with the surface such that it leaves on the incident side without change in frequency. Reflected light? This depends on the surface property!

17. Types of Reflection Functions Ideal Specular  Reflection Law  Mirror

18. Types of Reflection Functions Ideal Specular  Reflection Law  Mirror Ideal Diffuse  Lambert’s Law  Matte

19. Types of Reflection Functions Ideal Specular  Reflection Law  Mirror Ideal Diffuse  Lambert’s Law  Matte Specular  Glossy  Directional diffuse

20. Materials PlasticMetalMatte From Apodaca and Gritz, Advanced RenderMan

21. Illumination Model Ambient Light  Uniform light caused by secondary reflections Diffuse Light  Light scattered equally in all directions Specular Light  Highlights on shiny surfaces

22. Ambient Light A =intensity of ambient light k a =ambient reflection coefficient Really 3 equations! (Red, Green, Blue) Accounts for indirect illumination Determines color of shadows A=R*C r + G*C g +B*C b

23. Total Illumination

24. Diffuse Light Assumes that light is reflected equally in all directions Handles both local and infinite light sources  Infinite distance: L doesn’t change  Finite distance: must calculate L for each point on surface Surface

25. Diffuse Light C = intensity of point light source k d = diffuse reflection coefficient = angle between normal and direction to light Surface C=R*C r + G*C g +B*C b

26. The reflected luminous intensity observed from an ideal diffusely reflecting surface is proportional to the cosine of the angle between the direction of the incident light and the surface normal Lambert’s Law Surface

27. Lambert’s Law Surface Beam of Light

28. Lambert’s Law Surface Beam of Light The intensity of the received light:

29. Lambert’s Law Surface Beam of Light The intensity of the received light:

30. Diffuse Light Where is the light source?

31. Diffuse Light Where is the light source?

32. Total Illumination

34. Materials PlasticMetalMatte From Apodaca and Gritz, Advanced RenderMan

35. Specular Light Perfect, mirror-like reflection of light from surface Forms highlights on shiny objects (metal, plastic) Surface

36. Specular Light C =intensity of point light source k s =specular reflection coefficient =angle between reflected vector (R) and eye (E) n =specular coefficient Surface

37. Finding the Reflected Vector Surface

38. Finding the Reflected Vector Surface

39. Finding the Reflected Vector Surface

40. Finding the Reflected Vector Surface

41. Finding the Reflected Vector Surface

42. Finding the Reflected Vector Surface

43. Total Illumination

47. Multiple Light Sources Only one ambient term no matter how many lights Light is additive; add contribution of multiple lights (diffuse/specular components)

48. Total Illumination

50. Other Lights Attenuation caused by fog, smoke Spot lights

51. Attenuation Decrease intensity with distance from light

52. Attenuation Decrease intensity with distance from light d = distance to light r = radius of attenuation for light

53. Attenuation Decrease intensity with distance from light d = distance to light r = radius of attenuation for light

54. Without Attenuation

55. With Attenuation

56. Spot Lights Eliminate light contribution outside of a cone How to create spot lights ?

57. Spot Lights Eliminate light contribution outside of a cone Surface Zero! If outside of the cone

58. Spot Lights Eliminate light contribution outside of a cone Surface Depends on the angle β β If inside the cone

59. Spot Lights Eliminate light contribution outside of a cone Surface cosββ

60. Without Spot Lights

61. With Spot Lights

63. Implementation Considerations Surface >90: no contributions

64. Implementation Considerations Typically choose Clamp each color component to [0,1]

65. Opengl Functions See section 17-11 how to set up light sources (light source pos - light source position and type - light source colors - radial-intensity attenuation - spotlights how to specify global lighting parameters how to specify surface properties

66. Next Lecture Shading Texture mapping & others Readings: HB 17-10, 18-1, 18-2 and 18-3