Using GIMP bump map tool
Preamble
I will eventually split this tutorial into two different levels.
The one on this page is for people reasonably familiar with the GIMP interface and image manipulation commands.
The second will be for people with very little experience of image manipulation programs and GIMP particularly. This will include screenshots for each step of the operations involved. When ready there will be title links for this more indepth tutorial.
What is a Bump Map?
A bump map is a way of superimposing one image onto another. The bump mapped image will appear to be raised (or recessed if inverted), with the image you are bump mapping it with.
A bump map example
Below is a map of Sulawasi. It is made up of three layers comprising of the sea (blue), border (yellow) and land (green).
Create your bump map datum
To bump map the land you will need to duplicate it
Layer » Duplicate Layer
select the land by clicking on it with the Select regions by colour tool and then change the colour to white
Edit » Fill with BG Colour
The background is white by default when you open GIMP.
Tip :
If the selection you want to use as a bump map is not one colour you can select the transparent region around it with the colour tool, then invert your selection
Select » Invert
Then fill with white.
Blur the bump map datum
Perform a Gaussian blur on your bump map datum
Filters » Blur » Gaussian Blur
This will soften the edges of the eventual bump mapped image. I used the default Blur Radius settings of 5px for this example and repeated the same blur to soften it further. You will need to experiment with this setting, depending on the size of your image.
Bump map your original land layer
In the layers dialogue select the original land layer. Now open the bump map dialogue
Filters » Map » Bump Map...
Here you are presented with various options for your bump map, the most important one is the top Bump Map: section. This is where you select the blurred bump map datum layer that you have just created.
The Preview option should be selected by default, this will show you how each of your adjustments effect your image before you proceed. Try adjusting the Depth option to see exactly what a bump map is. In this example I've left the options at their default settings.
Tip :
Selecting the Invert bumpmap will recess, rather than raise, the bump map on your image.
Saving your image
When you have finished your bump map you can delete all the layers you no longer need, merge the layers you're keeping and save your image. In this case I've deleted the 'blurred land' bump map datum.
A bump mapping shortcut
I have included all the layers seperately on this bump map download page.
