# 原理化毛发BSDF#

Tip

## 输入#

### 通用选项#

Hint

$\sigma_{a} = \frac{\ln(Color)} {\left(5.969 - 0.215\beta_{N} + 2.532\beta_{N}^{2} - 10.73\beta_{N}^{3} + 5.574\beta_{N}^{4} + 0.245\beta_{N}^{5}\right)^{2}}$

Hint

$melanin\_qty = -\ln(\max(1.0 - Melanin, 0.0001))$

Hint

The ratio formula is: $$eumelanin = Melanin×(1.0-MelaninRedness)$$, $$pheomelanin = Melanin×MelaninRedness$$.

$\begin{split}\sigma_{a} = eumelanin × \left[\begin{matrix} 0.506 \\ 0.841 \\ 1.653 \\ \end{matrix}\right] + pheomelanin × \left[\begin{matrix} 0.343 \\ 0.733 \\ 1.924 \\ \end{matrix}\right]\end{split}$

Hint

IOR

Hint

The melanin concentration is multiplied by $$randomFactor$$, where $$randomFactor = 1.0 + 2.0×(Random - 0.5) × RandomColor$$.

Hint

### Chiang 模型#

The Chiang model is based on a Gaussian distribution with separate roughness along and orthogonal to the hair.

Hint

### Huang 模型#

The Huang model is based on microfacet based reflection and transmission, and supports elliptically shaped hair.

The ratio of the minor axis to the major axis of an elliptical cross-section. Recommended values are 0.8~1 for Asian hair, 0.65~0.9 for Caucasian hair, 0.5~0.65 for African hair. The major axis is aligned with the curve normal, which can be created with geometry nodes, but is not supported in legacy particle hair.

Microfacet roughness for reflection and transmission.

Optional factor for modulating the first light bounce off the hair surface. The color of this component is always white. Keep this 1.0 for physical correctness.

Optional factor for modulating the transmission component. Picks up the color of the pigment inside the hair. Keep this 1.0 for physical correctness.

Optional factor for modulating the component which is transmitted into the hair, reflected off the backside of the hair and then transmitted out of the hair. This component is oriented approximately around the incoming direction, and picks up the color of the pigment inside the hair. Keep this 1.0 for physical correctness

## 属性#

• 怀特 （黑色素 ：数学：'0'）

• 亚麻色 (黑色素值设为 $$0.25$$)

• 淡红色 (黑色素值设为 $$0.5$$)

• 棕色 (黑色素值设为 $$0.75$$)

• 黑色 (黑色素值设为 $$1$$)

BSDF

## 参考文献#

This shader is an implementation of the papers by Chiang et al. [CBTB16] and Huang et al. [HHH22].

[CBTB16] (1,2,3)

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. doi:10.1111/cgf.12830

[EFHLA11]

d'Eon, E. , Francois, G. , Hill, M. , Letteri, J. and Aubry, J. (2011), An Energy‐Conserving Hair Reflectance Model. Computer Graphics Forum, 30: 1181-1187. doi:10.1111/j.1467-8659.2011.01976.x

[HHH22]

Huang W., Hullin M.B. Hanika J. (2022), A Microfacet-based Hair Scattering Model. Computer Graphics Forum, 41: 79-91. doi:10.1111/cgf.14588