I was wondering, I have a human model for which I’ve applied a normal map symmetrically, but the normal map on the side being mirrored renders with reversed normals (what’s supposed to appear going inward goes outward, etc…). If the only way is to apply the mirror modifier and bake another normal map, is there a way to duplicate the UV islands I already have set up for the first half and apply them to the second half, kind of use them as a template?
Thank you.
if you used the mirror command then before doing the mirror you need to reverse all the normals on the copied object then joint them !
if you use the mirror modifier this is done autonatically for you
may be you could Ctrl-A your obejct before applying the mirror!
hope it helps
No, I’m sorry, it doesn’t help. That doesn’t really apply to what I’m dealing with, but thanks for the effort.
then try to upload file with model
i’ll test it and check how to do it !
hope it helps
It’s a little too big to be uploaded (it’s over 70 MB at the moment), and I don’t think I’d want it up for grabs anyway. Maybe if I bump the thread again somebody else can have a go at the solution from what I’ve described. Thanks, though.
Hi,
Make sure your UV islands are on just one half of the UV map. Select Mirror U in the mirror modifier. You don’t need to apply the mirror modifier for this to work.
Don’t forget that the image you use for the UV map must be symmetrical (left-right symmetry) for this to work as expected.
I’m sad to say, that in blender the normal map mirroring on uv-level doesn’t work like it does for an example in 3ds max. 
rawpigeon,
could you explain that in a little more detail, please? I don’t understand the UV islands being left-to-right symmetrical and on one half in the setup I have; I have a 4096 x 4096 map comprised of three separate groups of islands organized by the objects to which they correspond. Trying to be space-efficient, I don’t know how I could make these symmetrical, because they’re just not, there’s stuff all over the place.
Felix_Kütt:
Yeah, I don’t know too much about 3ds Max’s capabilities, but I think it’s major downfall is the whole $3500 dollar thing 
Hi,
See the attached .blend file. In it you will find Suzanne, who has been cut in half and had a mirror modifier added. I’ve unwrapped her, and given her a UV map. Have a play with it to make sure you understand what Mirror U does. It sounds like you might need to modify your image and your UV map.
UVMirror.blend (476 KB)
Rawpigeon: That’s not useful here at all; what TheRiddler wants is to use the exact same UV space, so what you’d get without Mirror U on. With a diffuse texture, that’s no problem, mirrors like you’d expect. With a normal map, it needs to realise that it has to flip some values to get correct results, which is a feature that Blender currently lacks.
TheRiddler: If you’re really desperate and your model is lowpoly, Marmoset Toolbag is a free model viewer on the engine used for Darkest of Days. It has drawbacks, but for me at least they don’t weigh up against the inability to mirror…
Hi,
I see what you mean. I guess it might be possible to use nodes to flip the normals the right way on one half of the object but it might be messy.
I suppose it would be possible to create a correct normal map for the other half, but it could involve using the existing normal map, flipping the normals on a copy of the object and baking to the object without flipped normals. It’s not exactly neat, but it might work. I’m too tired to think it through properly though, and I’m afraid I can’t really explain what I’m thinking!
Hope you figure something out.
Alright,
Well, if I were to apply the mirror modifier to get two separate, distinct UV sides of the object, is there a way to have Blender modify these new islands to mirror the islands I’ve already (painstakingly) created?
I appreciate the attention on the subject so far, guys.
I figured out how to get mirrored UVs so it’s very possible that’d be a way to go, but I figured there must be some kind of a solution to the problem I’ve ineffectually attempted to explain above, so I’ve included a screenshot of the problem. The right red oval focuses on the way I’d like the normal map to appear, as though it’s a clothing fold indentation, and the left red oval shows the mirrored side, which displays the fold indentation as coming out of the surface, which you’d think wouldn’t happen since it’s a mirror of the correct side (and the side to the image’s right, the one showing the indentation correctly, is the side I’ve been editing and has a mirror modifier applied to it).
Would this be better served moved to another forum, or is it okay here?
