GIMP Icon Tutorial- By Etain
1. Open up your image. I used a picture from Aethereality Gallery and cropped it down.

2. Duplicate the layer.

3. Go to Colors/Components/Color Mixer

4. I used these settings. You can adjust yours to whatever seems good for your icon.

Output channel: Red

Red: 185.2
Green: 0.0
Blue: -93.3
Output channel: Blue

Red: 66.7
Green: -4.4
Blue: 60.7

My icon turned out to look like this after doing the color mixer.


5. Go to Colors/Color Balance. Again, these are just my settings, you can adjust yours to your liking.

Highlights

Cyan - Red: 26
Magenta - Green: -6
Yellow - Blue: -83
Shadows

Cyan - Red: -100
Magenta - Green: -3
Yellow - Blue: 3
Midtones

Cyan - Red: -98
Magenta - Green: 35
Yellow - Blue: 43

The result :

6. Merge all the layers by clicking CTRL + M and click on Clipped to image.

7. You can skip this step if you like. But since I like my icons to be nice and bright, I brightened it a little bit by going to Colors/Brightness-Contrast.

Brightness: 6
Contrast: -2

8. Sharpen the icon. How much the sharpness you use depends on how your icon is. I myself used 54. You can sharpen your icon by going to Filters/Enhance/Sharpen.

9. Add some text, some brushes, and then you're done!

End result (after playing around with it):


Other icons made with this:

I hope this tutorial helped you. :D This tutorial was made by ETAIN.