Alpha contribution – Determines the appearance of the object in the alpha channel of the rendered image.
Normal (1) – A value of 1.0 means the alpha channel is derived from the transparency of the base material. Ignore in Alpha (0) – A value of 0.0 means the object does not appear in the alpha channel at all and shows the alpha of the objects behind it. Black Alpha (-1) – A value of -1.0 means that the transparency of the base material cuts out from the alpha of the objects behind. Matte objects are typically given an alpha contribution of -1.0. Note that this option is independent of the Matte surface option (i.e. a surface can have an alpha contribution of -1.0 without being a matte surface).
Ignore Objects in Secondary – When enabled, no other scene project objects are reflected or refracted by this material. All reflection and refraction rays instead sample the corresponding environment color or texture.
