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The Model
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
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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.
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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.
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TRT
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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
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it is
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dimmer than R and TT. In many other hair materials this is referred to as the secondary highlight.
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The following images show a final image and each component rendered separately.
Final | R | TT | TRT |
Material Parameters
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Before explaining the parameters of the material in detail, take note that :
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Parameter | Description | ||
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Hair 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. | ||
Quality | |||
Samples | The | diameter of one hair strand. The wider the hair the more it absorbs light. 3Delight first computes the absorption levels from Hair Color and then multiplies that absorption by this parameter to get the actual absorption inside one hair strand.number of samples to use for the monte carlo simulation for the hair in-scattering. | |
Scattering Depth | The depth at which you want to stop ray tracing scattering events. Use a value of 1 or more to receive proper back-scattering (transmission) when the hair is strongly back-lit. Start with 0 and increment this value of small steps, until visual demand is satisfied. | ||
Roughness | |||
Synchronize | This checkbox keeps in-sync the roughness values for the R, TT, TRT lobes. | Roughness||
Reflection Roughness | Specifies the roughness of the hair strand for the calculation of the Reflection, Transission, and 2nd Order Transmission respectively. They range from 0 (rough) to 1 (smooth). Note that, in a real hair strand, roughness should be the same for all the components. They are separate here for artistic control but should be kept the same if realism is desired. | ||
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. | |||
Positions | |||
Synchronize | This checkbox keeps in-sync the position shifting values for the R, TT, TRT lobes. | ||
Reflection Positions | Shift along the hair direction the position of the Reflections. | ||
Transmission Positions | Shift along the hair direction the position of the Transmission. | ||
TRT Positions | Shift along the hair direction the position of the Secondary Reflections. | ||
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. |
Material Output Variables
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