zbrush: high poly to low poly normal map

Zocky

Hello!

I have a question...lets say i created high poly rock with zbrush. Now i exported that into maya and retopo to make low poly mesh and uv map it. Since high poly mesh also has poly paint, i'd prefer to use zbrush to generate normal and color maps. Now i'd like to import low res mesh from maya back into zbrush.

So now, the problem is, i have this high res rock mesh with polypaint, and this retopo low poly mesh. How to i make normal map between the two inside zbrush? Is there way to import both as subtools, and then somehow generate normal map between the too?

cryrid

You'd probably get a much better result decimating the high-poly sculpt in zbrush, then exporting it and either baking in Maya or in xnormal (the latter can handle polypaint data for sure). You can bake in zbrush, but I don't think it cares about vertex normals/smoothing groups, projection cages, and god only knows about the tangent basis.

But if you wanted to try it regardless, load your sculpt up and use ZPlugin: Subtool Master: Multi Append. Choose your new retopologized mesh. With it selected, subdivide it a few times so that it can handle the same level of detail, and use Tool: Subtool: Project All to transfer the detail from the sculpt to the new model (the sculpt subtool needs to be visible, and you'll want RGB or MRGB on to transfer the polypaint as well). Then you can use Tool: Texture Map and Tool: Normal Map to create the maps, or the Multi Map Exporter Plugin

Bek

Yep. Load your High poly ztool, then import your low poly. For memory, Zbrush will give you a message saying that the topology of the mesh has changed, Y/N to transfer High Poly details to new mesh? CLick yes and your new low poly mesh will be subdivided to the level of your old HP then its details will be projected onto your new mesh.

Then I recommend you use the Multi Map Exporter plugin from http://www.pixologic.com/zbrush/downloadcenter/zplugins/

You can now export the normals and diffuse maps, as well as the new low poly model (If you've projected high poly details, the low will have changed slightly)

However, you could also use xNormal program to bake the normals, which should give you better results / more control than Zbrush. See http://eat3d.com/free/zbrush_xnormal for an example of what xnormal can do.

edit: lol ninja'd. Also, you might want to look into setting up GoZ between Maya and Zbrush, might make going from Maya to Zbrush and visa versa quicker.

Zocky

I see, so i don't have to use zbrush, that's good.

So, how can i export with polypaint? Is it enough to simply export as obj?

Also, tnx!

--edited--
@Bek,
But if i subdivide my low poly mesh, won't it produce wierd geometry, since it may have triangles and similar things?

cryrid

It's that simple. Just make sure the polypaint / colorize isn't turned off when you export the model, and you should be good

Zocky

I mean, i tried what you suggested already, but if i only delete few edge loops, even on simple model, the projected new mesh has errors, so i can't imagen what it would do to decimated low poly mesh?

Bek

I don't think subdividing your low will matter, since it's only the first level that you're going to be using. It's just that all the higher levels are needed to hold the high poly detail from your older high poly mesh. Anyway I'd recommend using the xNormal method anyway, but it's handy to know both. In some situations, you might get better results from the new low poly matching the high poly closer because zbrush has made them one and the same. In other cases you might not want your lowest level to change at all.

Awhile ago I made a simple rock this way: Made a cube in Modo > Divided it to have a few more polygons > UV map was already made

GoZ'd the model to Zbrush
Sculpted, subdivided, sculpted
Low poly of course changes along with this
Polypainted, use noisemaker etc
GoZ'd low back to Modo
Relaxed UV's (Possibly I missed turning smooth uv's on in zbrush when dividing, so had to do this)
Exported low from modo
Exported high from Zbrush
Imported both into xNormal
Baked normal, diffuse, AO

Zocky

Yeah, i'll try to use xnormal, but as you said, it would be handy to know both ways.

Still, as i said, i always have problems, when i project. level 1 is ok, but new max level isn't, it usually has either mesh errors, or polypaint errors.

--- edited ---

Oh, found some nice eat3d vid that explains this stuff, very nice!

And tnx both of ya for help, you guys are so damn fast. :P

cryrid

so i can't imagen what it would do to decimated low poly mesh?

You don't decimate the low poly mesh, you decimate the highpoly mesh so that you can export it to other applications instead of trying to load a 12million+ vertex model into Maya.

Zocky

yes i understand that, but as i understood the other way that was suggested, i would retopo or decimate high poly to achive low poly mesh (ingame mesh), and then re-project high poly onto this low poly, so that the low poly would get subdivided to max level and would get same shape. But if i do that, low poly version usually doesn't have topology that is best for zbrush....

and then i would use regular zbrush normal map generation.....but as i said, projecting high poly on subdivided low poly usually with me, ends with weird results because of weid topology (when it comes to zbrush)....

encore

Zbrush XNormal workflow [3D Motive Sample Content] by Galen Davis.

Bek

If you're decimating your high poly to get a low poly, you shouldn't be reprojecting details to it. I can't see a point to doing that anyway..

Zocky

ah that eat3d vid explains it very nicely. tnx!

cryrid

i would retopo or decimate high poly to achive low poly mesh (ingame mesh), and then re-project high poly onto this low poly, so that the low poly would get subdivided to max level and would get same shape. But if i do that, low poly version usually doesn't have topology that is best for zbrush....

Don't decimate the high poly to create the low poly; it's not meant for that, and so the results are going to be bad.

If you retopologize it correctly, you shouldn't see any issues with t he projection. Triangles and the topology aren't going to matter as much as long as you dont have long thin triangles all fanning to a single vertex, or are trying to keep the low poly mesh insanely low. It can help to adjust the projection settings, and project after each subdivision rather than just importing the new mesh on top and having goz try and project things automatically.