Is it necessary for hi res meshes to have UVs for baking normal maps?

Inhert

Is it really necessary to have UVs in the hi res mesh? The reason I ask is that my low res cage does have UVs on them but I didn't bother to update my hi res mesh in Zbrush with the new low res topology. Yes I know about importing your new retopologize mesh into Zbrush and transfering all the details but is this a necessary step?

I tried generating a normal map in Xnormal with my low res mesh that had UVs and my hi res mesh without UVs. Somehow I got some of the details from my high poly sculpt transferred over to my normal map but not as crisp as I want it to be. Am I doing this all wrong by skipping a step?

Uliss

You dont need to have UVs on you HP.
Only LP must have UVs.
To get more crisp results from Normal Map try to encrease the map resolution.

Chris Bruin

Your high poly mesh does not need UV's to bake a map, but do confirm that the normals are pointing the right way. Since you are baking in XNormal, you do not need to update the topology of the high res mesh. Try increasing your render resolution and turn up antiailising for the render.

cupsster

as most common case NO but this depends on technique you are using.. eg your hi poly can have detail normal map which you may want to transfer to low poly then it is required to map it somehow. this is highly dependent on your workflow.

Mark Dygert

Not nessesary unless you want to also capture any materials that are applied to your high poly.

For example you might be working on a statue and you applied a stone texture to your high poly, it can be helpful to capture that materials bump/normal and diffuse coloring, it properly accounts for stretching in the UV layout of your low poly and will flow across UV seams where doing that stuff later in photoshop can be tedious and time consuming.

Wood grain is another one that helps to capture from the high poly.

cryrid

Since you mentioned zbrush, then no, UVs are not necessary on the highpoly sculpt for baking normal or diffuse maps. They'd only be needed if you were baking inside of zbrush (since it requires the highpoly and lowpoly mesh to be the same tool).

Inhert

Thanks guys for the reply. I am working on a game soldier character for a mod. The texture resolution I am working on is 1024x1024 for the entire model all on one UV tile. Although I'm not sure what the head of the mod team wants in terms of texture resolution so I just went with 1k since this is somewhat of a standard resolution for games without sacrificing too much quality on the texture maps.

Last night I did some tests in Xnormal on just the shirt transferring details from the non UVed hi res mesh to the UVed hi res mesh and the results were far more better in terms of details being transferred over to the low res mesh. Although I got better results from it I didn't test the low res shirt with the UVs packed with the rest of the other models. Meaning that the resolution on the shirt in terms of ratio is far smaller than before I packed it. I'll try and post some screenshots so you guys can see the results.

TrampledUnderFoot

If you're not sure of the res, I would always go bigger than what you need. It's a simple step to downsize, but up-rezing is going require a re-bake and new textures.

Ace-Angel

Since you're using XN, here are a few things to note.

-You can unwrap your HP and do a UV-bake, I'm not sure how much more beneficial this is to a standard Cage bake, but it might help with uber-low poly bakes especially if you have the details where you need them to be exactly, without stretching.
-Upsize your bakes to double the original res, if you're baking non-micro detail and downsize to half the size.
-Most people tend to have (usually) 2K textures for the entire gear of a character (clothing, belts, pants, etc), save for reusable assets, like guns for example and pending on game-type, 1 or 2K for the organic parts in total (hand, feet, face, etc).

HOWEVER, the going back to the '2x bake res and downscale' point I made, you need to always make sure the detail you're baking will fit in an original map.
I made the mistake a few times where I baked a full art-nouveau kit for a character on a 2K map, downscaled it and bam, everything looked like a PS1 non-linear filtered texture full of tiny squares on it, so I honestly don't suggest willy-nilly 2:1 baking of textures without knowing before hand if the texture will even look good, especially once you have done all of your painting and maps at the 2:1 size.

So I suggest always baking at 1:1 scale first before a 2:1 process. Ofcourse, XN is pretty fast, so you could always bump up the AA to 2, since the baking time is negligible, 4x will take a little bit longer, but nowhere near as long as it might take you in other apps, and it will give just the same results you would get with a 2:1, even better sometimes.

Lastly, make sure you UV shells are Normalized (EI: meaning they take the same UV shell space as in 3D space size with the other models that will be in the same unwrap, there are a few plugins that allow this) it's important, especially on very low poly models, so you can gauge if something needs more textures space due to it's importance, or you want everything to share the same 'quality' in terms of details on your textures.

Inhert

Okay so I just baked a new normal map for just the shirt that had the UVs already packed with the rest of the models and there is not much difference in quality. Still the same 1k texture size. I've attached some images of the end result. Keep in mind that these are not really rendered images but rather just screenshots from the Maya viewport.

I have numbered which shirt was unpacked and packed. Number 1 is the unpacked UVs and number 2 is the packed UVs. Everything looks fine at a distance until I noticed a seam on the left side of the shirt when zoomed in close, on the right side it looks fine and hardly noticeable but on the left there is clearly a line (I'm talking about the packed UV version). The detail on the left side of shirt also seems off where the seams should meet. I'm not going to worry about it as much since it is going to be covered by a vest or some other modular items on top of it.