Layering Normal Maps

[Jero3d]

Hi guys, I've been trying to layer 2 normal maps inside one shader and I can't quite figure out what is the right way of blending them. I tried mixing them, adding them, multiplying and subtracting the difference but I can't get them to look correct. As a reference I combined the 2 normal maps in Photoshop by overlaying the red and green channels and multiplying the blue one and I still couldn't get it to match in Mantra. 

 

In my file you can see that I have the displacement texture nodes and I'm plugging them into the baseN, and then you can compare it with the displacement texture that is already loading the layered normal from Photoshop. The only way I found of doing this in Houdini is going inside the displacement texture node and doing the same I did with Photoshop combining the RGB channels right before they go into the Displacement node and the normals are calculated. The problem is that it's not a very elegant solution, and I also have the problem that I can't do this with a bump and a normal, so I'm trying to figure out how I can layer the normals themselves, not the textures with the color data. 

 

How can I blend 2 normal maps together, or 1 normal map and a bump map? Is there any way of doing this manipulating the normals or will I always have to resort to blending the RGB channels and then getting the value of the normals?

 

Here are the renders showing the difference between the layered normals in Photoshop and the one where I add the normals together:

 

 

Here is the file with the textures.

layerNormalMaps.zip

 

Cheers and happy new year!

[konstantin magnus]

There is "normal combine" in COPs. More information:

http://blog.selfshadow.com/publications/blending-in-detail/

Edited March 30, 2018 by konstantin magnus