Interreflections and Radiosity :

1

• Interreflections and Radiosity
• The Forward Problem
• Lecture 11

Thanks to Kavita Bala, Pat Hanrahan, Doug James,
Ledah Casburn
2
(No Transcript)
3
Cornell Box
blue hue
red hue
4
(No Transcript)
5
(No Transcript)
6
Phong Shading
Plastic looking scene

• no object interactions

• no shadows

7
Ray Tracing
Scene doesnt look realistic enough.

• where is the corner of room?

• is window flush with wall?

• is the carpet and wood supposed to be this dark?

8
Radiosity todays topic
Indirect lighting affects realism.

• room has a corner

• window has depth

• carpet and wood on table
• is lighter

• walls look more pink

9
The Rendering Equation Graph Style
p
source
viewer
p
p
Reflectance from Surfaces
Emission (light source)
Visibility (shadows)
10
(No Transcript)
11
Diffuse Interreflections - Radiosity

• Consider lambertian surfaces and sources.
• Radiance independent of viewing direction.
• Consider total power leaving per unit area of a
  surface.
• Can simulate soft shadows and color bleeding
• from diffuse surfaces.
• Used abundantly in heat transfer literature

12
Irradiance, Radiosity

• Irradiance E is the power received
• per unit surface area
• Units W/m2
• Radiosity
• Power per unit area leaving
• the surface (like irradiance)

13
Planar piecewise constancy assumption

• Subdivide scene into
• small uniform polygons

14
Power Equation

• Power from each polygon

• Linear System of Equations

15
(No Transcript)
16
(No Transcript)
17
Form Factors Invariant
18
Form Factor Computation

• Schroeder and Hanrahan derived an analytic
  expression
• for polygonal surfaces.
• In general, computing double integral is hard.
• Use Monte Carlo Integration.

19
Form Factor Computation
20
Form Factor Computation
21
(No Transcript)
22
Linear System of Radiosity Equations
Known
Known
Unknown

• Matrix Inversion to Solve for Radiosities.

23
(No Transcript)
24
Doug James
25
Wireframe
26

• Classical
• Approach
• No
• Interpolation

27
Wireframe
28

• Classical
• Approach
• Low Res

29

• Classical
• Approach
• High Res
• More accurate

30

• Classical
• Approach
• High Res
• Interpolated

31
(No Transcript)
32
Sample Scenes
33
Sample Scenes
34
Sample Scenes
35
Sample Scenes
36
Sample Scenes
37
Summary
38
Doug James
39
Two Pass Solution

• First Pass Diffuse Interreflections
• View independent, global diffuse illumination
• computed with radiosity.
• Second Pass Specular Interreflections
• View dependent, global specular illumination
• computed with ray-tracing.
• Combine strengths of radiosity and ray-tracing.

40

• Interreflections
• The Inverse Problem
• Lecture 12