Normal map of mirrored object acting weird

Voidrofl

Hello, i seem to be having a weird problem with the normal map of a model. It is a cat, which is made by making one half of it, then using mirrored copy and manually connecting the halves (did not use the auto merge vertices option because some weird lines appeared, so did it manually). When i bake the normal map, everything on the COPY side shows alright, but on the ORIGINAL side it shows some weird squares and stuff (the UVs for mirrored parts overlap). I have attached images of the ORIGINAL side (i have circled the problem areas), COPY side and UVs. If needed, i can also upload the models. If someone has a solution for this problem or can give me a pointer, i'd be really thankful.

Bartalon

When baking any texture maps you do not want mirrored UV shells to be stacked on top of each other. You will want to offset one of them (preferably the mirrored shell) by 1 unit in any direction of UV space. If you bake with them stacked, your software will try to lay down two different sets of information (one from each side of the model) into the same UV space which will result in strange artifacts.

The squares you are seeing line up with the edges of your polygons which leads me to think your model's hard/soft edges are not set up properly. You want your model to be completely soft except along UV texture seams. There is a whole lot of math involved with baking normal maps, and it is very dependent on vertex normals. This thread explains in more detail.

Proper smoothing splits, as they are called, will resolve a lot of your dark lines along your texture seams as well, as seen around your cat's back and paws.

Voidrofl

Thanks, will check that thread you linked and take your advice and try it out again, hopefully the problem gets solved

Voidrofl

Aight, so things are getting wierder and wierder. I did the offset by 1 unit, still the same result (i also tried to overlap them AFTER the bake, again same thing). I noticed something interesting tho. I tried to put the two mirrored pieces separate but both IN THE BAKE SQUARE, and it works correctly. I have attached six images (original side, copy side and UVs; the images that start with 2 are the experimental ones, and i have circled the area with which i have experimented; the experimental images are in the post below due to 4 images per post limit)

Voidrofl

Experimental images

kanga

Could be I am not understanding the situation but, you should bake the model with the sections you want to mirror deleted on the lowpoly. After you have baked and applied the textures to your model select the polys you want to mirror, duplicate them and detach them from the main model. Flip them and attach them to the main model again, weld verts if needed an you are done. The attached uvs of the mirrored parts will be on top of the original ones but only the polys will be mirrored, not the uvs.

Hope that helps.

Eric Chadwick

You should never delete half before baking a normal map. This will definitely cause a lighting seam, because the tangents are being changed after the bake.

You should always bake with the whole mirrored model... just move the mirrored UVs 1 unit outside from the UV square, then bake. Here's a pic
http://wiki.polycount.com/wiki/Texture_Baking#UV_Coordinates

Bartalon

If you are still experiencing weirdness after offsetting your UVs, setting up smoothing splits, etc. then I would suggest taking a look at your topology next. Your current screen shots show a less than favorable edge flow and you have quite a few ngons in various areas--it's very possible you could have some extruded faces sitting on top of each other, unwelded edges, or something else entirely that's causing the bake to produce normal artifacts.

kanga

So how do you guys do it? Delete parts of the mesh, do the uvs, copy, flip and weld parts into place before baking?

Eric Chadwick

I remove the mirrored half, and also remove any parts which use duplicated UVs. I create and pack my UVs. I mirror the model, and duplicate the UV-reuse parts... this mirrors/duplicates the UVs automatically. I select all the mirrored/duped UVs and move them 1 unit. Then I bake.

kanga

Thanks, will have to try it!