Sorry, can't help you much with Gimp. I don't understand how it manages alpha channels. For example: in photoshop you can simply select the channel and do whatever you want to do (and we want to do some basic stuff like copy or paste), but in Gimp - it wont let me paste into alpha channel. Maybe it requires to delete existing channel and create new? And try to hide an alpha channel - you wont see RGB channels as well. (Unnecessary obstacles, just like Blender
) Another thing: it displays AO map alpha channel inverted, and I know its not inverted, because I just reworked one of O01 textures just couple of minutes ago in PS, so not sure how you should proceed in Gimp: invert or not. But anyway, you, maybe, know Gimp better, so I will write how I do it:
1) open your ships texture (don't load mip maps), make it black and white (colors > desaturate) then adjust it with curves (colors > curves), so it looks similar to this:
Try not to leave too much white or grey areas, the more detail the better it will cover AO tex, the less shininess on your sub.
2) Once done, select all, copy; open AO tex, select or create alpha channel, paste. Both textures should be of the same size.
3) Save as (or export in gimp) dds (dxt5 (bacause of alpha channel), generate mip maps).
You may also want to use xnview as image viewer, you hit ctrl+h, and can show or hide alpha channel.
