1. Shading Variation in observed color across an object
strongly affected by lighting
present even for homogeneous material
caused by how a material reflects light
depends on
geometry
lighting
material
therefore gives cues to all 3
[Philip Greenspun]
© 2004 Steve Marschner • 1

2. Recognizing materials
Human visual system is quite good at understanding shading
[Dror, Adelson, & Willsky]
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3. metal dielectric Simple materials © 2004 Steve Marschner • 3 Materials
- physics -> conductors and insulators
(mirrors and glass)
- complex interface -> glossy behavior
- complex subsurface -> diffuse
© 2004 Steve Marschner • 3

4. Adding microgeometry
© 2004 Steve Marschner • 4

5. Classic reflection behavior
ideal specular (Fresnel)
rough specular
Lambertian
© 2004 Steve Marschner • 5

6. Diffuse reflection Light is scattered uniformly in all directions
the surface color is the same for all viewing directions
Lambert’s cosine law
Top face of cube receives a certain amount of light
Top face of 60º rotated cube intercepts half the light
In general, light per unit area is proportional to cos  = L . N
© 2004 Steve Marschner • 7

7. Lambertian shading Shading independent of view direction
illumination from source
diffuse coefficient
diffusely reflected light
© 2004 Steve Marschner • 8

8. Lambertian shading Produces matte appearance [Foley et al.]
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9. Diffuse shading
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10. Q Lambertian Shading In which configuration does the Lambertian
surface appear brightest?
(A)
(B)
(C)
(D)
© 2004 Steve Marschner • 11

11. Specular shading (Phong model)
Intensity depends on view direction
bright near mirror configuration
© 2004 Steve Marschner • 12

12. Specular shading (Phong model)
Intensity depends on view direction
bright near mirror configuration
© 2004 Steve Marschner • 13

13. Specular shading (Phong model)
Intensity depends on view direction
bright near mirror configuration
specularly reflected light
specular coefficient
© 2004 Steve Marschner • 14

14. Phong model—plots Increasing n narrows the lobe [Foley et al.]
© 2004 Steve Marschner • 15

15. Phong variant: Blinn-Phong
Rather than computing reflection directly, just compare to normal bisection property
© 2004 Steve Marschner • 16

16. Specular shading Phong and Blinn-Phong [Foley et al.]
© 2004 Steve Marschner • 17

17. Diffuse + Phong shading
© 2004 Steve Marschner • 18

18. Q Specular Shading In which configuration does the
specular surface appear brightest?
(A)
(B)
(C)
(D)
© 2004 Steve Marschner • 19

19. reflected ambient light
Ambient shading
Shading does not depend on anything
add constant color to account for disregarded illumination and fill in black shadows
ambient coefficient
reflected ambient light
© 2004 Steve Marschner • 20

20. Putting it together
Usually include ambient, diffuse, Phong in one model
The final result is the sum over many lights
© 2004 Steve Marschner • 21

21. Lighting Coefficients Q
What are the coefficients for this rendering?
kAmbient = 0, kDiffuse = 0, kSpecular = 0
kAmbient = 0, kDiffuse = 0.5, kSpecular = 0.5
kAmbient = 0.5, kDiffuse = 0.5, kSpecular = 0
kAmbient = 0.5, kDiffuse = 0, kSpecular = 0.5
kAmbient = 0, kDiffuse = 0, kSpecular = 0.5

22. Diffuse + mirror reflection (glazed)
(glazed material on floor)
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23.
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25. [levoy]
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26. Isotropic vs anisotropic
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29. BRDF Q
(A)
(B)
(C)
(D)