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| Info |
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Before explaining the parameters of the material in detail, take note that :
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Parameter | Description |
|---|---|
Color_______________________ | This is the color of one hair strand. It is defined as: 1.0 - Absorption. Absorption inside a hair strand is the main parameter driving the overall look of hair. Fair hair has small absorption levels (Hair Color is closer to white), while dark hair has high absorption (Hair Color iscloser to black). When absorption levels are low, light scatters more so "glow" is more apparent. |
Cuticle Angle | This values, expressed in radians, expresses the slope of each cuticle on a hair strand. |
Index of Refraction | The index of refraction of each hair strand. |
| Roughness | |
Longitudinal | |
Azimuthal | |
Primary Multiplier | |
| Weights | |
Reflection Weight | The contribution of Reflection (R) to the final result. |
Transmission Weight | The contribution of Transmission (TT) to the final result. |
TRT Weight | The contribution of 2nd Order Reflection to the final result |
| Note that the different weights are actually a balance between the different components. In other words, the weights are normalized so as to conserve the overall energy in the system. | |
| Glints | |
Strength | The intensity of the glint effect, which are caused by caustics reflections inside the hairs and are typically driven by the roughness of the reflections. |
Softness | Wether the glints are sharp or soft. |
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Technical Details
The shader simulates 3 scattering events from one single hair strand and then proceeds with a Monte-Carlo simulation to follow light paths inside the hair volume.
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R is the light directly reflected from the surface of a hair strand. In many other hair materials this is referred to as the primary highlight. TT is the transmission of light through the hair strand and interacting with the interior of the strand (absorption). This is responsible for the back lighting visible through the hair when a light is behind a hair clump. TRT is the secondary reflection of light traveling through the hair twice before going back to the same side it entered. As this light path gets absorbed twice it is dimmer than R and TT. In many other hair materials this is referred to as the secondary highlight. The following images show a final image and each component rendered separately.
Final |
R |
TT |
TRT |
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