Notice: I have another language version of The Gimp. When i say what the menus are named, they are probably named something else. Don't worry. Finding them is easy.
Step 1 - FaQ
What is alpha skinning?
A simply way to remove weapons, body parts, etc. from models without editing the model, by using Alpha Channels.
What's a "Alpha Chanel"?
It's "Alpha Channel. Two N:s. Seriously, it's a layer on all BLP:s that makes all parts in it invisible on the model.
Step 2 - Getting started.
Open up The Gimp and Wc3 Viewer. Start with the Viewer.
Select the treewiev. Check "blp." Browse through the skins. For this example, we chose the Centaur Khan skin. When you have chosen your skin, press the Extract and Convert BLP button at the top of the screen.
(the button is recognized as the blue box with an arrow going from it)
Choose to export is as TGA: it will make the alpha channels stay.
Now, open up The GIMP. Open your file. To learn how to use GIMP, i suggest using it's help files.
Step 3 - Alpha Skinning
Select the freehand marking tool. It's the lasso icon. "Lasso" the outlines of what you're going to remove.
When you're done marking, select the "Layers" dropdown menu. Go to the "Transparency" menu. You should now see several options concerning Alpha Channels.
Pick the "Treshold Alpha" option.
------ Common problem!
if the option "Treshold Alpha" isn't active for you, that means GIMP won't accept the already existing alpha layers. At the top of the Layers menu, there should be an option to add layers. Add a Transparency layer. That should make the option availible.
Move the marker to 255.
Step 4 - What happened?
Save your skin. Next, open the Viewer again. Now, open the model that uses the skin you edited. When it's on the screen, click on it and press ctrl + M. A list of skins you've used will show up.
Find the original file path for the skin you edited. Click "change".
Browse to your edited alpha file. Select OK, and the part you alphaed should... vanish into thin air. ;)
Step 5 - Hey! It's not working
Didn't this work for you?
The part i alphaed out is partly/completely team coloured!
You alphaed out a part with team colout on it. Sorry, but in GIMP, there's no way to fix this. Alpha out another part of the skin instead.
Thanks for reading. //Rabarber
If you found a typo, say where you found it, and i'll correct. If you have info that you think is missing from this tutorial, tell me. I'll add it if i feel like doing it.