OmniHairBase

OmniHairBase is a physically-based material designed base on Walt Disney’s Hair and Fur Model [1], capable of modeling near-field stylistic and realistic hair, fur, and fiber. This documents the base features. The non-base material has direct texture mapping parameters and is a standalone uber materials.

OmniHairBase comes with a small set of parameters with intuitive meanings, ranges and predictable results.

Parameters

Color

Hair shading simulates color through melanin properties and explicit color control:

• Melanin concentration and type (eumelanin/pheomelanin ratio) model biological hair pigments

• Base color overrides provide direct RGB control for non-natural hair colors

• Both methods affect surface color and internal light scattering

Parameters

Display Name	Name	Type	Default
Base	base_color_weight	float	1.0
Color	base_color	color	1.0, 1.0, 1.0
Melanin Presets	melanin_concentration_preset	enum	melanin_concentration_custom
Melanin	melanin_concentration	float	1.0
Melanin Redness	melanin_redness	float	0.5
Melanin Randomize	melanin_concentration_randomize	float	0.0

The hair fiber absorption can be controlled by setting the color parameter or adjusting the melanin concentration parameter.

Note

In the path-tracer mode, overlapping hair fibers with low melanin concentration or light-color dye may appear dark. To reduce the darkening, one may need to increase the Max Bounces setting.

Please see RTX Interactive (Path Tracing) mode render settings for more information.

Max Bounces: 4

Flamingo Hair Dye

Max Bounces: 256

Flamingo Hair Dye

Note

In the RTX – Interactive (Path Tracing) mode, to reduce the noise within hair fibers with low melanin concentration or light dye color, one may need to increase the Total Samples per Pixel setting.

Please see RTX Interactive (Path Tracing) mode render settings for more information.

Total Samples per Pixel: 8

Icy Light Blue Hair Dye

Total Samples per Pixel: 32

Icy Light Blue Hair Dye

Total Samples per Pixel: 64

Icy Light Blue Hair Dye

Total Samples per Pixel: 256

Icy Light Blue Hair Dye

Base

This parameter sets the brightness of the hair fiber color.

Base: 0.1

Green Ombre Dye

Base: 0.25

Green Ombre Dye

Base: 0.5

Green Ombre Dye

Base: 1.0

Green Ombre Dye

Color

This parameter sets the hair fiber color by adjusting the absorption within the hair fiber volume. The color parameter can create a dyed or art-directed hair look.

Pretty Purple

Rainbow

Note

For dyed hair, one should set the melanin concentration parameter to 0.0; otherwise, melanin and pheomelanin will darken the dye color.

Tip

For realistic hair color, set this parameter to white, and adjust the melanin concentration parameter instead.

Melanin Presets

This parameter presents a list of known melanin concentration values for different hair types. One can use a custom melanin concentration by setting this parameter to melanin_concentration_custom and enter a value for the melanin concentration parameter.

Melanin concentration “presets” are including:

Fiber Color	Melanin Concentration
White	0.0
Platinum Blond	0.0025
Light Blonde	0.10
Dark Blonde	0.30
Dark Brown	0.65
Black	1.0

Melanin

This parameter sets the melanin concentration, which controls the hair fiber’s primary color. At 0.0, hair fiber appears completely translucent, while at 1.0, pigments blocking refracted rays. Thus the hair fiber becomes black.

Melanin Concentration: 0.025

Platinum Blonde / Silver

Melanin Concentration: 0.05

Shimmering Sands Light Blonde

Melanin Concentration: 0.1

Sun-Kissed Light Blonde

Melanin Concentration: 0.2

Blonde

Melanin Concentration: 0.35

Light Brown

Melanin Concentration: 0.5

Brown

Melanin Concentration: 0.75

Dark Brown

Melanin Concentration: 1.0

The Crow - Black

Melanin Redness (Pheomelanin)

This parameter sets the melanin redness, which is the ratio between brown eumelanin and red pheomelanin. At higher values, the hair fiber becomes redder. The melanin redness has no effects when the melanin concentration parameter is 0.0.

Melanin Redness (Pheomelanin): 0.0

Melanin Redness (Pheomelanin): 0.5

Melanin Redness (Pheomelanin): 0.75

Melanin Redness (Pheomelanin): 1.0

Melanin Randomize

This parameter randomizes the amount of melanin concentration within hair fibers.

Note

The melanin randomization is not supported yet, one may map a texture noise to the melanin concentration parameter instead.

Melanin Randomization: 0.0

Melanin Randomization: 1.0

Specular

Hair specular creates characteristic highlights and shine through surface reflection (primary), internal reflection (secondary), and light transmission through strands. Each component controls distinct reflection behavior.

Parameters

Display Name	Name	Type	Default
Roughness	specular_reflection_roughness	float	0.2
Anisotropic Roughness	specular_reflection_anisotropic_roughness	bool	false
Azimuthal Roughness	specular_reflection_azimuthal_roughness	float	0.2
IOR Preset	specular_reflection_ior_preset	enum	ior_custom
IOR	specular_reflection_ior	float	1.55
Shift (deg)	specular_reflection_shift	float	3.0

This hair model classifies light paths based on the number of internal reflections. Light paths are named after their event type. The first three light paths are R, TT, and TRT, where R indicates a reflection and T a transmission event.

These primary light paths are modeled as separate lobes with a dedicated longitudinal and azimuthal roughness. In contrast, longer light paths are implicitly accounted for a fourth lobe without additional parameters.

While the fourth lobe needs no azimuthal roughness, the longitudinal roughness of the fourth lobe is set to longitudinal roughness of the “third lobe”.

Roughness

This parameter sets the longitudinal roughness of the reflection along the hair fiber. At 0.0, reflection becomes sharp and bright, while at 1.0, a deviation based on specular_reflection_shift in degrees, for a very rough reflection.

Roughness: 0.2

Roughness: 0.3

Roughness: 0.4

Roughness: 0.5

Anisotropic Roughness

This parameter enables the use of the azimuthal roughness parameter. When disabled, the roughness parameter controls both longitudinal and azimuthal roughness.

Azimuthal Roughness

This parameter sets the azimuthal roughness of the reflection in the hair fiber’s tangent direction when the anisotropic roughness parameter is enabled. At a lower value, the reflection looks sharp, while at a higher value, reflection wraps around the hair fiber, giving a smoother look.

One could consider azimuthal roughness as a phase function of the hair fiber’s volume, which changes the translucency and affects the multiple scattering albedo.

Azimuthal Roughness: 0.0

Anisotropic Roughness: Disabled

Azimuthal Roughness: 0.1

Anisotropic Roughness: Enabled

Azimuthal Roughness: 0.3

Anisotropic Roughness: Enabled

Azimuthal Roughness: 0.5

Anisotropic Roughness: Enabled

IOR Preset

This parameter presents a list of known IORs (index of refractions) for various materials, including hair and wet hair. One can use custom IOR by setting this parameter to ior_custom and a value for the specular reflection’s IOR parameter.

IOR

This parameter sets the index of refraction. Individual hair fibers are modeled as dielectric cylinders, with hair fiber reflecting off and transmitting into the fiber depending on the IOR.

At a lower IOR value, hair fibers exhibit strong forward scattering, while at a higher IOR value, stronger reflection.

Tip

The IOR for typical human hair is about 1.55. A lower value can give hair fibers a muted look, while a higher value gives a wet look.

Muted and thick hair

IOR: 1.2

Wet hair

IOR: 1.8

Shift (degree)

This parameter sets the angle of the hair fiber’s scales. values above 0.0 shift the primary and the secondary specular reflections away from the hair fiber’s root, while values less than 0.0 shift the specular reflection toward the root.

Recommended values for human hair:

Hair Origin	Scale angle (degrees)
Piedmont	2.8 ± 0.2
Light brown European	2.9 ± 0.3
Dark brown European	3.0 ± 0.2
Indian	3.7 ± 0.3
Japanese	3.6 ± 0.3
Chinese	3.6 ± 0.4
African-American	2.3 ± 0.4

Shift (degree): 5.0

Shift (degree): 10.0

Shift (degree): 15.0

Shift (degree): 20.0

Diffuse

Diffuse reflection in hair shaders controls how light scatters through the hair fiber’s cortex. This property affects the overall base color visibility and soft scattering behavior of hair strands under direct and indirect lighting.

Parameters

Display Name	Name	Type	Default
Weight	diffuse_reflection_weight	float	0.0
Color	diffuse_reflection_color	color	1.0, 1.0, 1.0

It adds a Lambertian diffuse component for greater control over the look of hair fibers.

Weight

This parameter sets the weight of the additional diffuse reflection component. At 0.0, the hair fiber exhibits specular scattering, while at 1.0, completely diffuse scattering.

Note

A healthy-looking human hair fiber does not have any diffuse component. However, the diffuse component can create effects such as makeup, dirty or damaged hair, and fabric threads.

Weight: 0.1

Weight: 1.0

Color

This parameter sets the color of the diffuse scattering component.

Color: Texture

Color: Texture

Emission

Hair emission controls self-illumination effects in hair strands, useful for creating bioluminescent or glowing hair effects. This property works independently of diffuse and specular properties

Parameters

Display Name	Name	Type	Default
Weight	emission_weight	float	0.0
Emission Mode	emission_mode	enum	emission_lx
Intensity	emission_intensity	float	1.0
Color	emission_color	color	1.0, 1.0, 1.0
Use Temperature	emission_use_temperature	bool	false
Temperature	emission_temperature	float	6500.0

This layer adds an additional directionally uniform EDF, which describes the light-emitting properties of the surface.

Note

Realistic hair fibers do not have any emissive property, and these are just for artistic control.

Note

In the RTX – Interactive (Path Tracing) mode, to reduce the noise in the indirectly lit area using emissive materials, one may need to increase the Total Samples per Pixel.

Please see RTX Interactive (Path Tracing) mode render settings for more information.

Weight

This parameter sets the amount of light emission from the surface.

Weight: 0.1

Weight: 0.6

Emission Mode

This parameter specifies the physical units to use for the emission intensity.

1. “Nit” is the unit of luminance and describes the surface power of a visible light source. The overall illumination of the scene changes depends on the size of the light source.

One nit is equal to one candela per square meter. 1 nit = 1 cd/m^2

The candela per square meter is the base unit of luminance. Candela is the base unit for luminous intensity.

A light source that emits one candela of luminous intensity onto an area of one square meter has a luminance of one candela per square meter or one nit. As an example, a calibrated monitor has a brightness of 120 cd/m^2 or 120 nits.

2. “Lux” is the unit of illuminance and describes the total amount of visible light that a light source emits. The overall illumination of the scene does not change depending on the size of the light source.

One lux is equal to one lumen per square meter. 1 lux = 1 lm/m^2

A light source that emits one candela of luminous intensity from an area of one steradian has a luminous flux of one lumen.

A light source that emits one lumen of luminous flux onto an area of one square meter has an illuminance of one lux. As an example, very bright sunlight has a brightness of 120,000 lux.

Intensity

This parameter sets the emission intensity. The emission mode parameter sets the physical unit for this parameter.

A few examples of illuminance under various lighting conditions:

Lighting Condition	Illuminance (lx)
Sunlight	100,000 - 120,000
Daylight	10,000 - 25,000
Overcast	1000
Twilight	10
Full moon	0.05 – 0.3
Ceiling lamp	400 - 800
Table lamp	200 - 300
Candle light	12.57

Color

This parameter sets the emission color.

Color: Texture

Color: Texture

Use Temperature

Enable the use of color temperature value instead of color.

Note

This parameter will override the default emission color, including any textures assigned to the emission color parameter.

Temperature

This parameter specifies emission color using a color temperature in the Kelvin unit. Lower values are warmer, i.e., redder, while higher values are cooler, i.e., bluer. The default value of 6500K is close to D65 illuminant, the white point in sRGB and Rec. 709 color spaces.

Emission Temperature: 2700.0

Emission Temperature: 4000.0

Emission Temperature: 6500.0

Geometry

The geometry section defines how special surface effects are calculated relative to the underlying 3D geometry. These parameters control opacity thresholds, and depth-based adjustments like opacity attenuation.

Parameters

Display Name	Name	Type	Default
Enable Opacity	enable_opacity	bool	false
Opacity	geometry_opacity	float	1.0
Opacity Threshold	geometry_opacity_threshold	float	0.0
Geometry Normal	geometry_normal	float3	state::normal()
Displacement	geometry_displacement	float3	0.0, 0.0, 0.0

Enable Opacity

Enables the use of opacity

Opacity

This parameter controls the travel of rays through the surface. At 0.0, the surface is invisible to the cameras, while at 1.0, it is completely opaque.

Note

Although it is not physically correct, one may reduce the opacity to create softer-looking hair fibers at the cost of increased render time.

Full Look

Opacity: 1.0

50% Hair-Thinning

Opacity: 0.5

75% Hair-Thinning

Opacity: 0.25

Haircut

Opacity: Texture

Opacity Threshold

This parameter controls the opacity threshold. At a value lower or equal to the opacity map, the surface renders completely transparent. At a value greater than the opacity, the surface renders fully opaque.

Geometry Normal

This parameter replaces the surface geometric normal with the one evaluated from a map.

Displacement

This parameter sets the direction and distance of position modification of the surface.

Important

This feature is not supported yet.

Presets

OmniHarBase comes with an existing library of presets. These presets can be used as a starting point for creating a new hair look.

Black	Auburn
Brown	Blonde

References

[1]

Georgiev, I, Portsmouth, J., Zap, A., Herubel, A., King, A., Ogaki, S. and Servant, F. (2019), Autodesk Standard Surface. Autodesk White Paper.

[2]

Chiang, M. J., Bitterli, B., Tappan, C. and Burley, B. (2016), A Practical and Controllable Hair and Fur Model for Production Path Tracing. Computer Graphics Forum, 35: 275-283.

[3]

Keis, K., Ramaprasad, K.R. and Kamath, Y.K. (2004), Studies of light scattering from ethnic hair fibers. J Cosmet Sci. 55(1): 49-63. PMID: 15037920.