Textures luminescence/shininess

[L0ck0n]

How to recreate stock textures luminescence/shininess? I know that KSP textures use alpha channel as a luminescence channel. I can extract this channel in GIMP to separate layer. But i can't recreate this in my textures, creating simple alpha channel transparency doesnt work. Do you have any tips on how to create textures with luminescence/shininess like that in KSP stock textures?

Edited November 9, 2018 by L0ck0n

[wasml]

You can add a alpha layer by right clicking on the layer and in the drop down selecting "Add Layer Mask" - a number of options for creating from copying the alpha channel to a gray scale copy of the layer. To edit - click on the new alpha layer (so it has a white border) and edit away. When your done right click on the layer and select "Apply layer mask" and it's merged back - or just leave it separate - when you export it's used as the alpha layer (I think).

[CobaltWolf]

I just go into the channel box in Photoshop and create an explicit alpha channel (which also saves me having to think in terms of transparency, I can just work with it as a separate grayscale map). Can GIMP not do the same?