Expanded metal with normal maps (VRayNormalMap)

Last year, Peter posted an interesting article on how to make nice looking expanded metal with displacement maps (this technique is covered here on my blog or here on BBB3 blog)

That reminded me an old project of doing this material only with opacity & normal map and after some research, it turned out great ! Good news is that it is very fast, much more faster than displacement. Actually, it is obvious since normal mapping is no more than an evolved bump map.

facade test

Technique is quite simple, but it took me some time to fine tune it and to get clean and believable results. Actually, this is the method used by many game developer to “map” hi rez geometry onto low poly game models, you’ll find many examples on sascha’s blog

Steps for tiling repetitive patterns are the following :

A – Make a mesh of what you want to turn into normal, as hi poly as you can.

B – extract a displacement map like explained earlier (here or here) grab an opacity map aswell if you have holes in you material. 16 bit png is the format to go.

C – Load the map in photoshop, aswell as the opactiy map, duplicate it and run the NVIDIA normal map plugin (download it here) with default paramters (I tired every possibility and the first was the better O_o)

D – Tweak the levels (CTRL-L) of every individual RGB channel of the normal map (see below) In this particular case, I modified symetrically only the red channel to enhance it (left-right channel) Notice how a blue channel is only filled with values above 127, this is because this channel refers to “towards-away” normals and you can’t have normals facing the back of the mapped geometry. Don’t mess with that ;)

See how the middle of the expanded metal is just mid grey, perpendicular to the plane

Curving this channel can help to twist the metal a bit more. I left this untouched

E – Crop the map so you can tile it, save the maps in PNG 8 bit, except for the displacement map that you can save

I made some test and the normal technique was approx. 10 times faster than the displacement one.

Below, examples of a simple plane mapped with this technique (two lights, one plane, one cam)

4 simple planes. Different values for the bump slot (50 & 100). Click to enlarge

I won’t give those map for free, you’ll have to recreate those by yourself… or if you’re lazy you can buy the maps on turbosquid here and here

Two important remarks when you load you maps in 3dsmax:

- Put the VRayNormalMap in the bump slot, select the bitmap as a sub-map in the VRayNormalMap dialog.

- Remember to override gamma of the loaded texture to 1.0 or your normals will be completely messed up !

- I think the value of the bump as to be set to 100, but I might be wrong. Values over 100 seems to return strange result but might work, further test will tell.

- Check no filtering and blurring 0.01 in the opacity map bitmap dialog to speed up opacity renderings.

Feel free to comment and/or to enlight this article with your insights !