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Python Bump Map Extractor Plugin for The Gimp
This is a Gimp plugin to extract a bump map from an image. It implements a technique based on this tutorial: http://www.cgtextures.com/content.php?action=tutorial&name=normalmap
Note that the useoop flag in the script (which is not exposed to the Gimp GUI, so you'd have to edit the script itself to change it) is setup in a way that is specific to my system so it won't work unless your paths are the same and you have the helper script (which is not in the git repo). It was an attempt to increase performance on multi-processor systems, but the benefit was very small and as you can see it complicated the setup quite a bit.
Also be aware that the only Method that will probably work correctly is 1 sample. I found that the noise reduction option pretty much eliminates the need for the other methods and they made the calculations more complicated/slow so I just stopped using them. At some point I will get around to removing that GUI option.
Unfortunately there's no way to do a live preview in a Python script, so I usually try out different parameters on a lower resolution copy of my image. This plugin takes a long time on high res images, so lowering the resolution speeds things up considerably.
The script can be found here: https://github.com/cybertron/gimp-plugins/blob/master/createbump.py Download it to your ~/.gimp-2.6/plug-ins directory and ''make it executable''. It will show up as "Create Bumpmap" in the Map submenu of the Filters menu.