Sigma

An example of Sigma showing reflections, absorption colour, and internal scattering of radiosity light.

For Sigma to work correctly you must remember to have Double Sided turned on.

Sigma is an 'energy conserving' material with subsurface scattering, so the sum of all the shading components will always equal 1. Be aware that as you increase the Specularity level, the amount of light that is available for Diffuse shading and subsurface scattering decreases. If you set the Translucency to 100%, there will be no Diffuse shading, and you will not see any bumps on your surface.

Specularity: This doesn't work like the old Specular level, but combines both Specular highlights and Reflections into one setting. The higher this value, the brighter both Specular highlights and Reflections will be.

Specular Color: This tints both Specular highlights and Reflections.

Gamma: This brightens or darkens the subsurface illumination by applying a gammacurve to it.

Absorption Color: This setting is not the colour of the inside of the material, but rather the relative levels of absorption of red, green and blue. For example, water would have a higher level of red and green absorption than blue, since it appears blue ( more blue light gets through ) the deeper you go.

Samples: This is simply the number of subsurface samples that are used to determine subsurface illumination for each pixel. The more samples, the less noise, and the longer it takes to render.

Advanced Shading: When this toggle is switched on, the Sigma material can look inside itself, so if you have a luminous object embedded inside a Sigma material, it will illuminate it from the inside.

An example showing a Sigma material being illuminated by a luminous ball inside the 'leg' where the beam passes through it.

Subsurface radiosity: This setting allows lighting from radiosity to be transmitted through the material. If you are lighting your object using luminous geometry or an HDR probe, you will need this turned on. If the setting is turned off, only direct light from Lights will be transmitted through the material.

Categories: Tutorials | Surfacing | Nodes | 9.2