Some Stellar materials provide a Roughness texture bank.
It is important to know that this texture is also used to change the Anisotropy value.
Therefor using a regular gray scale image is not recommended as it will influence both parameters.
To change either the Roughness or the Anisotropy value, the color channels of an RGB texture must be prepared accordingly:
1. make sure the R (red) channel of an RGB texture contains grayscale values (black = no roughness, white = full roughness).
2. make sure the G (green) channel of an RGB texture contains grayscale values (black = no anisotropy, white = full anisotropy).
Note: the B (blue) channel is currently not evaluated and has no influence to the rendering.