ZBrushCentral

Mirroring a Normal Map

ZBrush Usage Questions
#1

I have a human figure and i want to just mirror half of her face(saving on texture space).
I had read you cannot mirror normal maps,but recently read somewhere that you could unwrap the head,move half of the UV’S out of the 0,1 UV square space.Create your Normal map and then move the Uv’s back overlaying the original half.
I tend to create my Normal maps in Zbrush.
Any advice would be greatly appreciated

#2

you can. Just remove half of the model, redo the UVs for just the half. Than you can use a mirror, clone or whatever its called in your modelling software. You can also flip uv islands as well and line them up with the opposing sides island so that the two islands are stacked on each other. I dunno if you can do this in just zbrush though. I haven’t really used the new uv tools in zbrush yet.

#3

you can never truly mirror a normal map…well, that’s not true.
if your render engine can support mirrored normal maps than you can, but you’re actually calling that normal map 2x to achieve this as well as a bit of math within the engine to mirror the channels inside of the normal map and display them on the mirrored half.

if you’re making the normals for a game engine this can be a very bad thing…well, “sometimes” It all really depends on the final output.

You can however fake with a couple of techniques, but there will always be a seam when generating normal maps…it’s just the nature of the beast.

What software are you using? what maps are you using? where is your actual seam? etc? knowing what you’re making and the software you’re using will help people to help you out in this regard. (Some software doesn’t have the ability to move UV’s over 1,0…well, they all can, but some take some tweaking.

#4

Thanks for the replies.

I am using 3d Studi Max 9 and Zbrush 3.5.

#5

I have also been wondering about this. I have been working on a work flow for creating game assets. I was thinking that using mirrored normal maps would be a great way to optimize my texture space.

My workflow so far has been.

  1. create my base mesh in Maya
  2. delete half of it and create uvs
  3. mirror the object and export it into zbrush
  4. sculpt the object with symmetry on
  5. decimate the object and export it into Maya
  6. use transfer maps to bake the AO and normals.

In the maya view port it seems to display correct, but if I do a render with Metal Ray it looks as if the normals are inverted on the mirrored side. I haven’t tried this in a game engines yet but I’m interested in both the Unreal 3 and Crytek engines.