The method I use is not exactly "expert" and may yield different results. However, it is easy and free, and produces acceptable results for me. What I do, is make a black and white copy of my image texture, then with GIMP's built in filters, I apply the bump map filter.

You can find this under:

Map→Bump Map.

You can then apply other effects, such as increasing the contrast, to achieve better results. I have used this to generate displacement and normal maps for planets, for instance. It's not necessarily a "professional" method, but it's easy and works well for small scale projects.

##Example:
This texture I used to generate a normal map on this asteroid:

Please note that it is not as clear here because the asteroid has an "atmosphere" on top. I also used other (procedural) textures for displacement.

The method I use is not exactly "expert" and may yield different results. However, it is easy and free, and produces acceptable results for me. What I do, is make a black and white copy of my image texture, then with GIMP's built in filters, I apply the bump map filter.

You can find this under:

Map→Bump Map.

You can then apply other effects, such as increasing the contrast, to achieve better results. I have used this to generate displacement and normal maps for planets, for instance. It's not necessarily a "professional" method, but it's easy and works well for small scale projects.

Example:

This texture I used to generate a normal map on this asteroid:

Please note that it is not as clear here because the asteroid has an "atmosphere" on top. I also used other (procedural) textures for displacement.