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
Ray traced image.
Image rendered with radiosity.
Original

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 for z-buffer & Gouraud Shading

46. Rendering Pipeline for z-buffer & Phone shading

47. Rendering Pipeline for List-priority Algorithm & Gouraud Shading

48. Rendering Pipeline for List-priority Algorithm & Phong Shading

49. Rendering Pipeline for Ray Tracing