Question about normal maps/adding details to surfaces and channels


I have very low poly models, nothing to really bake, and I want to add some details like scratches to a surface with a normal map. Or bump map?

I want to paint it in Photoshop and as it seems there are 2 methods I could use.

1- use a seamless map and just attach it as normal map in UE4. But what kind of map would this be? I only find those black/white maps with scratches. Aren’t these specular maps? I don’t want a wooden table or a wall to be shiny.

2- load the UV template of my model in Photoshop, add some scratches and use the Nvidia plugin to convert it to a normal map.

I think I’ll rather try 2, since I don’t want the scratches to be all over, only in certain places.

Now my question - I have in 3dsmax channel 1 for my texture. It’s a tileable texture I am using and the faces overlap on the whole map, so they just fit on the model. Also the back of the wall is on the front of the wall.

Channel 2 is my lightmap, here nothing overlaps.

Now I wonder if I can make a third channel for the normal map, because I want certain damage on the back of the wall, but not on the front, so I don’t want to use my first channel since here the faces overlap.

I would just load the UV template of the lightmap in Photoshop, paint it, convert it and use this as Normal Map since all faces are nicely separated. BUT - Can I tell UE4 which channel to use for the normal map? Can a model have different unwraps for different maps?

I hope my question is understandable.

The black and white maps are probably alphas or height maps, and are actually a lot more useful than a normal map. You can turn a height map into a normal map with the NVidia tools, or really any professional tool. You can even just use heightmaps in UE4 as normal maps using the height-to-normal function (but dont do this unless you have to, it’s not exactly cheap).

You’d actually be better off using either Marior Substance Painter to texture things this way, but yes this is a good way to do it.

Yes, you can use different UV channels for different textures. Just plug in a ‘Texture Co-Ordinates’ node and set the UV channel there (remembering that indexes always start at 0).

The way I’d do it though is a hybrid of both of these methods.
Keep the normal map being applied to the whole mesh the same way the diff texture is (so go with method 1 there), but then use a ‘wear’ map (mask) and paint that as a black and white texture (using method 2) and lerp between a ‘0,0,1’ node (blank normal) and the detail normal texture.
That way, you can define exactly where you want the scratches effect to be applied, but you don’t have to worry about the normals being on different texels to the diffuse map, and it gives you a lot more control and freedom.

Hey, thanks for the reply!

I’m not sure if I got this right.

Do you mean the mask with using my UV template?

Before I used something like this:

Is this what you mean with mask? I used the green/red outputs in UE to define some effects for the red and green part and it worked just fine.

But I don’t get how I should paint such a mask when the faces overlap. Like a wall that shares back and front with one part of the texture. I would need to divide the parts somehow, so I would need a different unwrap that separates front and back faces. Or do I just not get it?