1. Gimp (FREE) [Must have x86 version!]: https://www.gimp.org/downloads/
- Grab the normal map plugin for Gimp: http://registry.gimp.org/node/69
- Place normalmap.exe and glew32.dll into C:\Program Files\GIMP 2\lib\gimp\2.0\plug-ins
- Place libgtkglext-win32-1.0-0.dll and libgdkglext-win32-1.0-0.dll into C:\Program Files\GIMP 2\bin
2. Open the diffuse image from what you want to create the bump map into two different tabs.
- Menu bar > Filters > Map > Normal Map
- Leave default settings and press okay
- Menu bar > Colors > Components > Decompose as RGB
- This should create a new tab
3. Switch to the decomposed image
- Rename layer 'red' to 'a'
- Rename layer 'blue' to 'g'
- Rename layer 'green' to 'b'
4. Switch to the untouched diffuse texture. This will be the specularity map.
- Menu bar > Colors > desaturate
- Menu bar > Levels
- Move the sliders until mainly the white shows. Don't make the image too sharp.
5. Copy the specularity image as a new layer to the decomposed image.
6. Rename this new layer to 'r'
7. Re-arrange the layers from top to bottom as red, green, blue and alpha.
8. Menu bar > Colors > Components > Compose as RGBA
8. Export image as BC3/DXT5 with GenerateMipMaps
You are done. You should see that the new *.dds will look green and similar to other X-Ray bumps.
_bump#.dds are created by the Image Editor panel inside of the Actor Editor or Level Editor within the SDK.