This page provides information on the V-Ray Hair Next Material.
Auto update – When enabled, the view in the swatch will update automatically every time one of the VRayMtl properties is changed. When the check box is not selected the swatch will not update automatically but you will be able to update it manually with the Update button.
Max resolution – Determines the maximum resolution of the swatch.
Update – When clicked, forces an update of the swatch.
Melanin – The pigmentation component that gives the hair strand its main color. The higher the value assigned, the higher the concentration of melanin and the darker the hair strands are. See the Melanin example below to understand how different values work.
Pheomelanin – The redness (pheomelanin content) of the hair strand as fraction of all melanin. 1.0 makes the hair redder. The ratio of melanin to pheomelanin determines how red the hair is. The pheomelanin amount will have no effect if the melanin is set to 0. See the Pheomelanin example below.
Dye Color – Applies a color tint to the hair. For a dyed hair look, set the melanin to 0, otherwise the melanin will darken the dye color and pheomelanin will introduce redness to it. White means no hair dye. See the Dye color example below.
Transparency – Controls the transparency of the hair. White is fully opaque, while black is fully transparent.
Diffuse Color – Controls the diffuse component of the shader. Use this for materials made out of cloth threads or other non-translucent fibers, as well as for dirty hair. Note that clean hair or fur does not normally have a diffuse component, so if you want to disable it, leave the diffuse amount at 0.
Diffuse Amount – Specifies the amount for the diffuse component of the material.
Glossiness – Controls the glossiness along the hair strand. It primarily controls the width of the highlight, essentially how shiny the hair appears.
Primary Glossiness Boost – Additional scaling factor to boost the primary reflection glossiness. This can be useful for reproducing the effect of shiny coating on rough looking fur.
Softness – Controls the overall softness of the hair by how much the highlights are wrapped around the individual hair strands. Higher values make the highlights wrap almost completely around the strands giving the hair a smoother look, while lower values make it look crisper. See the Softness example below.
Highlight Shift– Shifts the highlights along the hair strand. Positive values shift the highlight away from the root of the hair, while negative values move the highlight closer to the root. Values in the range 2-4 are typical for human hair. See the Highlight shift example below.
Ior – Hair index of refration. The typical value for human hair is 1.55. The higher the value, the more reflective the hair strands. See the IOR example below.
The Glint rollout provides control over the Glint (focused highlight) and the Glitter (focused colorless highlight) parameters.
Glint Strength – Controls the strength of the colored highlights across and along the strand.
Glint Variation – Adds a random glint variation along the strand. It affects the glint strength and orientation; the original secondary highlight strength and orientation; the softness, glossiness and highlight shift.
Glitter Strength – Controls the glitter strength. Glitter is the additional more focused colorless highlight, which is randomly scattered along the strand. It is more pronounced with hard lighting produced by small or collimated light sources.
Glitter Size – This parameter controls the size of the randomization pattern applied. Increasing the value increases the size of the pattern.
Scale – Internally, the variation along the strand is set in real world units. This parameter allows correction of the appearance of hair not modeled in real world scale. Values below 1.0 shrink the variation pattern, while values above 1.0 elongate it.
Values below 1.0 shrink the variation pattern; values above 1.0 elongate it, so the effect is spread out.
The Randomization parameters can be used to introduce variation of the general parameter values. When using randomization, different hair strands will receive slightly different values for the below parameteres, so in fact the randomization works on a per strand basis.
Random Melanin – Adds variation to the amount of melanin in each hair strand.
Random Dye Hue – Adds variation to the hue component of the dye color. This makes each strand appear with a different dye color. This parameter has no effect, when the dye color is not used, i.e. when the dye color is pure white.
Random Dye Saturation – Randomizes the saturation of the dye color between hair strands. This makes each strand appear with a more or less saturated dye color. This parameter has no effect, when the dye color is not used, i.e. when the dye color is pure white.
Random Dye Value – Adds variation to the value component of the dye color. This makes each strand appear with a brighter or darker dye color. This parameter has no effect, when the dye color is not used, i.e. when the dye color is pure white.
Random Gray Hair Density – Adds variation to the number of gray hair strands. You can also assign a texture map to this parameter to specify areas where the density is higher.
Random Glossiness – Randomizes the glossiness of each hair strand.
Random Softness – Assigns a random value for the softness parameter for each strand. This makes some hair strands appear crisper, while other appear softer.
Random Highlight Shift – Adds variation to the highlight shift for each strand. This offsets the highlights closer or further away from the root of the hair on a per strand basis.
Random IOR – Randomizes the ior value for each hair strand. This makes some strands more reflective, and others - less reflective.
Random Tangent – Adds a random offset to the hair tangent. This makes the hair stands receive light from slightly different directions, which also means that the highlights will be placed in slightly different places for each strand. Note that this parameter is depends on the scene scale.
Primary Tint – The color tint for the primary component. Corresponds to the light reflected off of the outer surface of a hair strand. See the Primary tint example below.
Secondary Tint – The color tint for the secondary component. Corresponds to the light piercing through and reflecting off of the back surface of a hair strand.
Transmission Tint – The color tint for the transmission component. Corresponds to the light going through the hair strands.
The color tint for the primary component. Corresponds to the light reflected off of the outer surface of a hair strand. In the example below the Primary tint color is set to pink (H=0,S=172,V=132) and we adjust the hue value and the melanin to 0.6.
Bounces – The number of indirect bounces used to compute the effect of the multiple scattering. It can significantly affect the hair appearance, especially for light colored hairs. The number of bounces necessary can vary from 5 for dark colored hairs, to 30 and more for light colored ones.
Subdivs – Controls the number of samples to use when defining the quality of the final rendering of the material. Lower values will render faster, but the result will be noisier. Higher values take longer but produce smoother results. This parameter is only available when Use local subdivs is enabled in the Global DMC settings. This parameter is not available when the renderer is set to CUDA.
Here is a list of links and references used when building the VRayHairNextMtl material.
 Chiang et al. "A Practical and Controllable Hair and Fur Model for Production Path Tracing" - 2016
 Pharr "THE IMPLEMENTATION OF A HAIR SCATTERING MODEL" - 2016
 d'Eon et al. "An Energy-Conserving Hair Reflectance Model" - 2011
 d'Eon et al. "An Energy-Conserving Hair Reflectance Model" post publication review - 2011
 d'Eon et al. "Importance Sampling for Physically-Based Hair Fiber Models" - 2013
 d'Eon et al. "A Fiber Scattering Model with Non-Separable Lobes - Supplemental Report" - 2014
 Marschner et al. "Light Scattering from Human Hair Fibers" - 2003
 Zinke et al. "Light Scattering from Filaments" - 2007
 Zinke (thesis) "Photo-Realistic Rendering of Fiber Assemblies" - 2008
 Jakob (thesis) "Light Transport On Path-Space Manifolds" - 2012
 Yan et al. "Physically-Accurate Fur Reflectance: Modeling, Measurement and Rendering" - 2015
 Yan et al. "An Efficient and Practical Near and Far Field Fur Reflectance Model" - 2017