Melanin
Melanin Redness
Dye Color
Specular Level
Roughness Along
Roughness Around
White Hair
Synthetic Fiber
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The 3Delight Hair and Fur material is an artist friendly, yet physically plausible, hair and fur shader. Internally, the shader relies on a Monte-Carlo simulation to explore the different light paths inside a medium (in this case, a clump of hair) to produce an image. The complexity of this process is hidden from the artist which controls only high level shader parameters such as color and roughness.
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Note the glow caused by light scattering inside blond and light coloured red hair. Also note how black hair has nice silky features. The "glint" is caused by caustics inside hair strands and is not an after thought of the shading model. All these features necessitate proper simulation of light scattering in hair clumps.
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Parameters Description
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Overall Look
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Color
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Longitudinal Roughness
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Azimuthal Roughness
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Primary Multiplier
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Components Weights
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Reflection Weight
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Transmission Weight
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TRT Weight
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Glints
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Index of Refraction
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Cuticle Angle
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Glint Strength
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Glint Softness
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Technical Description
An interesting aspect of hair rendering is that all the intricate visual details seen in hair stem from the scattering of light in a multitude of hair strands and is not due to the complexity of the BRDF on a single hair strand. This seemingly simple observation explains why so many complex shaders are not successful at conveying a realistic look for hair. This includes the widely used shaders based on the Marschner model not using volume scattering. 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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- There are is diffuse component. Most shaders have an ad-hoc diffuse term to approximate the soft look of hair. In reality, this soft look is caused by light scattering and is not related to a classic diffuse BRDF.
- No control over directly reflected color. Direct reflections have the same color as the incoming light. Any coloured visual features are due to light passing through a strand of hair.
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Melanin
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Melanin Redness
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Dye Color
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Specular Level
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The three main components of light scattering: Reflection (R), Transmission (TT) and 2nd Order Reflection (TRT).
Roughness Along
Roughness Around
White Hair
Synthetic Fiber
Dye Hue Variation
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.
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Final
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R
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TT
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