Since I started using Blender, I have been using GIMP to make my bumpmaps. Usually I just took the colormap and did the following to it:
- Desaturate the layer
- Invert the colors
- Adjust the brightness (to 15) and the contrast (to 90)
Then I would import it into Blender in its own texture channel, map it to the rendered normals, and call it good. The problem I have been encountering, however, is getting different quality of bumps, so to speak, on the same bumpmap.
This problem became especially apparent as I was modeling the upper floor of Building A, an older exposed timber work structure. How would the beams look – well, like wood beams – and the stucco more smooth? Then it occurred to me that, just like I make the colormaps in GIMP using layers, perhaps I should also try to make the bumpmaps with layers, too. And this is what I got:
Although I still need to work on the texture for the beams a bit – the wood grain runs (strangely) in the same direction for all of the beams – I am pleased with how it was possible to make a distinct contrast between the strongly-grained timbers and the smoother stucco. I think that I will revisit the bumpmaps for all the models I have developed thus far and tweak them bringing them into Unity3D.
Update: And here is a quick render of the model with a new and improved bumpmap:
Looks a lot more interesting and realistic, although for complete realism I suppose that I would have to check out a book on how to construct exposed timber work houses in Germany. Something else for my “to-do” list I suppose.
David Neville, PhD, MS 
I use a plugin for photoshop that nVidia made that helps with bump mapping alot. You even have multiple options for it as well. I like it. I don't know if they have a gimp version.
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Thanks, RemixedCat, for the tip. I like GIMP because of the price, but personally I prefer Photoshop in terms of how the program “feels” when I work with it. I'll keep my eyes open to see if GIMP has a plugin similar to the one that nVidia made for Photoshop.
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