Rendering Diamonds

1
Rendering Diamonds

• Seminar Light Color in Nature
• Sabine Fischer
• 6.02.2004

2
Main aspects of rendering diamonds

• why render diamonds?
• reflection
• Fresnel term
• refraction
• Snells law
• dispersion
• spectral sampling

3
Why people render diamonds

• they look interesting
• test whether a new cut shows interesting color
  effects
• product preview in online shops

4
Fresnel term

• how much of the light is reflected?
• approximation ignore polarization

5
Snells law

• used to calculate the refracted ray direction
• total internal reflection when the square root
  is not defined

6
Overview Dispersion

• wavelength dependant refraction
• ways of describing an objects dispersive power
• a simple implementation

7
Measures for dispersive power

• in optics two main ways
• how to get the refractive index for wavelength µ?
• linear interpolation
• interpolate between a few values

8
Composite Spectral Model

• color can be represented as a spectral
  distribution
• Fourier transform
• sum of a smooth component and several spikes

9
Composite Spectral Model

• in practice
• sample the smooth part
• easy spectral multiplication
• monochromatic rays are spikes without a smooth
  component

10
Spectral sampling

• in reality continuous dispersion
• possible
• trace spread rays covering a certain angle
  (expensive)
• trace sample rays for several wavelengths

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How to sample?

• wavelength sampling
• problem what is the contribution of each ray to
  the final color in rgb?
• convert wavelength to rgb (expensive or
  inaccurate)
• rgb values will likely not add up to white

12
Spectral sampling artifacts

• using too few sample rays leads to artifacts

13
Useful things to note

• what recursion depth to set?
• adaptive recursion with ray significance
• how to illuminate?
• area light sources
• directional light
• when a ray leaves the scene, calculate
  illumination based on ray direction

14
Recursion depth
15
Two rendered diamonds
16
Summary

• reflection refraction
• Fresnel term Snells law
• dispersion spectral sampling
• a possible approach
• Composite Spectral Model
• sampling artifacts

17
The End

• Thanks for listening.
• Ask questions.