Hair - Specular

Primary Specular

Glossiness

Glossiness of the primary specular component. The higher the value, the tighter and sharper the specular. Internally, this corresponds to the exponent of a cosine power. For realistic hair, the value should be in the range 5 to 500. When Glossines is zero, the specular BRDF behaves like a perfect diffuser, reflecting the same amount of light in all directions.

Weight

Scale of the primary specular contribution, which simply multiplies the primary specular color. It is strongly recommended to keep within the 0 to 1 range. In particular, values above 1 will create energy out of nowhere and break energy conservation and possibly introduce more noise than necessary.

Color

The color of the primary specular component. For realistic and clean hair, the color should be set to white.

It is also possible to assign texture maps to the specular color attribute. The image on the left is an example of some hair that has been rendered with a brown specular color. On the right is the same hair that has been rendered with a fractal texture connected to the specular color attribute.

Angular Shift

Angular shift of the primary specular in degrees. It controls the shift of the specular lobes away from the perfect mirror direction and is used to control the offset of the specular highlight along the hair strand. For realistic results, it should take a negative value, typically in the -10 to -5 range.

Secondary Specular

The Hair shader has a secondary glossy specular lobe with its own Scale, Color, Glossiness and Shift controls. The secondary specular tends to shift towards the root of the hair, which is achieved with a positive value in the Shift control. Even though in real hair the secondary shift is linked to the primary shift with the expression secondary shift = primary shift * -1.5, the specular shift controls are decoupled for greater artistic control.

The secondary specular usually shifts 1.5 times as much towards the root as the primary specular. It is also wider than the primary specular. The Scale of the secondary specular defaults to 0 to preserve behaviour when using materials from earlier versions.

 


Glossiness

Glossiness of the secondary specular component. The higher the value, the tighter and sharper the specular. Internally, this corresponds to the exponent of a cosine power. For realistic hair, the value should be around half the primary specular glossiness, i.e. it's slightly rougher due to scattering when light goes through the hair fiber.

Color

The color of the secondary specular component. For realistic and clean hair, the color is usually non-white, tinted by absorption inside the hair fiber.

Weight

Scale of the secondary specular contribution, which simply multiplies the secondary specular color. It's strongly recommended to stay in the 0 to 1 range. In particular, values above 1 will create energy out of nowhere and break energy conservation and possibly introduce more noise than necessary.

Angular Shift

Angular shift of the secondary specular in degrees. It controls the shift of the specular lobes away from the perfect mirror direction and is used to control the offset of the specular highlight along the hair strand. For realistic results, it should take a positive value. A suggested expression is to link the primary and secondary specular shift values together like: secondary specular shift = -1.5 * primary specular shift.