hey, thank you for your effort tho i found another way to achive what i wanted.
i used the gimp-normalmap plugin (can be found on google code archive - "cant post links here") to do the converstion tho there was a problem that the plugin did not let me do that so i had to change one line in the code and compile it myself. That was pretty easy on linux but a little harder for windows but i got it working.
Not sure if i am allowed to share that modification but if so i can provide the compilled dll.
The only thing i did there was to change line 202 to:
nmapvals.alphamap_id = 0;
this was causing the plugin to crash when i was using it from NONINTERACTIVE gimp console so i changed it, not sure if that is the right solution but it did work for me sofar, so good enough
![Wink ;)](./images/smilies/icon_wink.gif)