Illumination and Shading

1. Illumination and Shading Prof. Lizhuang Ma Shanghai Jiao Tong University

2. Contents • Illumination Models • Shading Models for Polygons • Surface Detail • Shadows • Transparency • Global Illumination • Recursive Ray Tracing • Radiosity • The Rendering Pipeline

3. Illumination Models • Ambient Light: • :intensity of the ambient light • :ambient-reflection coefficient: 0~1 • Diffuse reflection: • :point light source’s intensity • :diffuse-reflection coefficient: 0~1 • :angle:

4. Diffuse Reflection

5. Examples

6. Illumination Models • :light-source attenuation factor • If the light is a point source • Diffuse reflection: where is the distance the light travels from the point source to the surface

7. Examples

8. Colored Lights and Surfaces • If an object’s diffuse color is • where for the red component • however, it should be generally • where is the wavelength then

9. Specular Reflection

10. The Phong Illumination Model • : specular-reflection coefficient: 0~1 • So, the Eq. can be rewritten as: • Consider the object’s specular color: • : specular color

11. The Phong Model

12. The Phong Illumination Model

13. Examples

14. Calculating the Reflection Vector

15. The Halfway Vector

16. Multiple Light Sources • If there are m light sources, then

17. Shading Models for Polygons • Constant Shading • Faceted Shading • Flat Shading • Gouraud Shading • Intensity Interpolation Shading • Color Interpolation Shading • Phong Shading • Normal-Vector Interpolation Shading

18. Constant Shading • Assumption • The light source is at infinity • The viewer is at infinity • The polygon represents the actual surface being modeled and is not an approximation to a curved surface: • Note that N.L ,N.V are constant across the polygon face

19. Gouraud Shading

20. Gouraud v.s. Phong Shading

21. Phong Shading

22. Texture Mapping = Pattern Mapping

23. Bump Mapping &Displacement Mapping

24. Shadows If light I is blocked at this point If light I is not blocked at this point

25. Shadows If light I is blocked at this point If light I is not blocked at this point

26. Scan-Line Generation of Shadows

27. Shadow Volumes

28. Shadow Volumes

29. Shadow

30. Transparency • Interpolated transparency • : transparency: 0~1 • Filtered transparency • :transparency color

31. Global Illumination Direct & indirect (reflected) light sources

32. The Rendering Equation • : intensity passing from to • : emitted light intensity from to • : intensity of light reflected from to from the surface at (indirect light sources) • : the distance between and • : all surfaces if is invisible from if is visible from

33. Recursive Ray Tracing surface normal reflected ray shadow ray transmitted ray

34. Recursive Ray Tracing surface normal reflected ray shadow ray transmitted ray

35. Traditional Ray Tracing

36. Ray Tracing + Soft Shadows

37. The Ray Tree Intensity of reflected ray Transmission coefficient :0~1 Intensity of transmitted ray

38. The Radiosity Equation • : radiosity of patch i • : rate at which light is emitted form patch i • : reflectivity of patch i • : form factor (configuration factor) • : area of patch i • Since • Thus

39. The Radiosity Equation • Rearranging terms • Therefore • Progressive refinement

40. Radiosity vs. Ray Tracing Original Ray traced image. Image rendered with radiosity.

41. Computing Form Factors

42. Hemisphere

43. Hemicube

44. The Rendering Pipeline • Local Illumination Pipelines • z-buffer and Gouraud shading • z-buffer and Phong shading • List-priority algorithm and Phong shading • Global Illumination Pipelines • Radiosity • Ray tracing

45. Rendering Pipeline forz-buffer & Gouraud Shading

46. Rendering Pipeline forz-buffer & Phone shading

47. Rendering Pipeline forList-priority Algorithm & Gouraud Shading

48. Rendering Pipeline forList-priority Algorithm & Phong Shading

49. Rendering Pipeline forRay Tracing