Normal map extraction.....is high poly required to have UV:s?

Hi Blender users. Im creating a character and Im creating a character in Zbrush. I have a low poly model with UV:s (also thinking about unwrapping in Blender to get a better UV set) but not on the high poly, and Im wondering whether high poly must have UV:s in order to extract details through a normal map onto the low poly in Blender? (I hope this is the right section to ask a question like that.) Thank you!!!

Does the high poly have a multires modifire? If so you can bake from multires in bake settings.
If not I do think you cna use a smart uv project on the highpoly mesh.

Hi. Thanks! No, its a high poly directly from Zbrush on the highest subdivision level, and one low poly from the lowest. I want to unwrap the low poly in Blender, as I get more control, but the high poly is just to dense to create any working UV:s. I want to extract the detail in Blender onto low poly one.

The highpoly mesh don’t need to have UVs when baking, only the lowpoly mesh does.

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Hi! Really? ok, great. Thank you so much for your help. I´m relieved now. I had some problems thinking about it.

One more question if that is ok. Can I freely texture paint the extracted normal map that is baked on the lowpoly model?

The baked normal map is just another texture file, you can modify it as you want, whether it is to fix some error or to overlay another normal map on top.

However the colors in a normal map convey very specific normal information that depends both on the mesh topology and the UVs, so unless you know exactly what you are doing I wouldn’t recommend manually editing it. If you need to, it’s much easier to re-bake the normal map than trying to change it by hand.

Hey Lillya.

Ah, that´s good to know. Thanks. What I meant is if I can texture paint with brushes the 3d model I have the normal map on? I intend to create a good UV set for it, but I Wonder if I can just paint on top of it? Maybe I didn´t understand your answer fully.

If you mean painting a color or roughness texture then yes, you can texture paint the model just fine, the normal map makes no difference when painting.

You mentioned creating a UV set, if you already baked a normal map then there’s no need to create another UV, you can use the same one for painting. You paint into different texture files but the UV can be the same.

You can paint color, roughness, and metalness in Blender or Photoshop and it will be ok.

However, you can’t paint the normal map because, as it’s been mentioned, every pixel of a normal map encodes a unit-length vector, and not every combination of the RGB values can be decoded as a unit-length vector - in fact, they have to adhere to a very particular formula ( sqrt( (r*0.5+0.5)^2 + (g*0.5+0.5)^2 + (b*0.5+0.5)^2) = 1 if I recall correctly ) - so if you alter them manually, it’s all but certain that you’ll break the math. The shader will of course draw something when given such a mangled normal map, but it probably won’t look good (unless you’re using a shader that automatically renormalizes - that is to say corrects - the normal map vectors, and even then you can have nonsensical discontinuities).

That said, if you have access to a specialized texture painting package, such as Substance Painter, or Mari, those have special tools to paint normal maps that won’t break the math.

I hope this fully answers your question.

ok, great thank you Lillya! No, I will just import both low poly and high poly and unwrap the lowpoly into a nice UV set. That´s the plan! The UV map coming out of Zbrush is not ideal for sure. Alot of learning ahead.

Thank you Piotr. Yes, that does help alot, and it is an interesting read. One learns everyday. I see, ok, well, then I will use Substance Painter to texture the character. Like you said, it is specialized and I wont have a headache trying to figure it out in Blender. (It would be cool if they implemented it though in the texture paint department). Once again, thank you.