I want to apply back to a high resolution mesh a normal map so that the actual position of the vertices would be changed a little bit accordingly.
It can be a way to get back the high res model from the low res + normal map
I think this is possible in zbrush (though I didn’t touch it in a while)
Is that possible in blender? I could not find it
If you are having trouble getting the displacment map “out of” the normal map, try the nvidia normal map photoshop plugin, and ‘convert to height’.
Thanks for your replies
That make the process a little complicate ;
Some guys are using the painting tool to modify the normal map, and that has some good results ; Hence I was thinking to apply the normal/displacement map frequently.
Also I don’t have a license of photoshop at home ; is there a open source way/independent to photoshop to make the conversion from normal map to displacement? I looked around and found out crazy bump is doing it, but it got not free anymore…
Try gimp here. It is a free image manipulating program like photoshop.The normal map plugin is here. Hope that helps.
Thanks for the informations!
Took me a while to realize that the plug-in in gimp was also allowing to convert a normal ma to a height map!
I tested also the plug-in from nvidia on photoshop.
On both it works well if I created the normal map with from a picture and then convert it to heigh map.
But I don’t get any good result at all with my own normal map:
http://img186.imageshack.us/my.php?image=resultsdisplacefromnmeu5.jpg
I have Gimp 2.6 and I don’t have any more that GTK folder which is mentioned in the Gimp normalmap’s readme.txt-file
“Place libgtkglext-win32-1.0-0.dll and libgdkglext-win32-1.0-0.dll
in the C:\Program Files\Common Files\GTK\2.0\bin directory”
Where should I put these two files now?
I don´t understand why you don´t bake the displacement map in Blender. Blender has the same capabilities of baking displacement maps or height maps as ZBrush. All you need is a low resolution object and a high resolution one. You select the high res object, then SHIFT select the low res, you go to the rendering panel, there you will find a sub menu called bake, you select ¨displacement¨, ¨normalized¨ and ¨selected to active¨, and then you will have to play with the distance number until you find the correct value for your model.
Oh, I was forgetting, previously to all that you also have to asign a 32 bit image to the low res model. You select it, go to edit mode, select all the faces, open the uv image editor, select all the faces in the uv map layout, then go to IMAGE, NEW and click the floating point option.
Here is a video tutorial I made for baking displacements map for a character of mine that is freelly distributed.
Don´t even try to convert a normal map to a height map!! Before Blender had these baking options I went nuts trying to do what you want to do. It is simply not possible to have an acceptable result. I ended up using a very old program that would bake 8bit height maps, and I could never manage to convert my normal maps to displacement maps, not even with Gimp, Nvidia, Xnormal or whatever other program there was.
If you don´t have the high resolution object, you´d rather remake it with the multires tools inside Blender and than follow the previous procedure to obtain the height maps…
@ lasioc: place them at the same place that the other library, in the gimp/bin folder. The “plug-ins” folder has also been moved to GIMP-2.0\lib\gimp\2.0\plug-ins.
@ jpbouza: thanks for the explanation. I knew this procedure to bake the displacement map, it’s good to see that you do it that way. My concern was actually the following:I used the “painting tool to modify the normal map”, a development made recently and working pretty well ; I was wondering if it is possible to transform the “virtual” modification made on the normal map with this painting tool to the “real mesh”.
You answered that question, as apparently it’s not possible to use this normal map to modify the mesh and not possible neither to get a correct displacement map from this normal map 
Thank you Ben