ZBrushCentral

zBrush to Maya displacement maps - inflated

ZBrush Usage Questions
#1

Hello,
I’ve been following 2 different tutorials, step by step exactly like they explain.
Those tutorials are:

Gnomon Workshop - ZBrush Production Pipeline-
http://www.thegnomonworkshop.com/dvds/mme02.html

Rendering Zbrush Displacement Maps in Maya-
http://www.zbrushcentral.com/zbc/showthread.php?t=25542

And in both cases I get an inflated, baloon like result…
In both tutorials you have to open the exported from zBrush TIFF file with Photoshop and turn it into RGB, I’m starting to think that after saving the file again, it messes with the grey values and that’s the reason for it.
I tried disabling color management in photoshop but that didn’t work.

So frustrated…
What should I do? :frowning:

Thanks.

#2

Are you restoring the base mesh prior to creating the displacement map? Or are you simply dropping to level 1 and immediately creating the map?

The thing about multi-res editing is that it’s affected by the catmull-clark algorithms that come into play when you divide the mesh. When you divide, the mesh is subdivided AND smoothed. That smoothing results in a contraction of the mesh. When you return to level 1 of the mesh, that contraction is carried back down as well. If you now create your map, it will be calculated based upon a model that is actually smaller than what the map will be applied to. As a result, all the displacement values are exaggerated, which in turn results in a puffy render.

When you return to level 1 you need to get back your original mesh – the one that the map will actually be applied to. One way to do this is to store a morph target before you ever divide the mesh. You can then switch to the stored morph target before you create the map. If you didn’t store a morph first, all is not lost. What you can do is go to level 1 and store the target now. Next, import your model again. This will replace level 1 and restore your base mesh so that you can create the displacement map.

Either way, you’ll now have a morph target at level 1 that lets you switch between the multi-res version of the level and the original base. Use the original base before creating displacement maps. Use the multi-res version before you return to higher levels. (Otherwise, the restored – larger – base mesh would end up affecting the higher levels when you go to them.)

#3

Thank you for your reply :slight_smile:
What I did was exporting the new level 1 mesh and using that in Maya, I believe it’s the smarter, more accurate way to do it if I don’t really need the original mesh.
The problem was that the “Alpha Depth Factor” stated after creating the displacement map is not correct!?
The tutorials explain that that detail is very important and that I should put it in the Alpha Gain in maya as well as minus and half of that parameter in the Alpha Offset… but it’s completely wrong, I had to put much smaller numbers in order for it to look allright, how come?

And the next problem I have is that I cannot use the displacement with Mental Ray approximation nodes…
For some I reason I get the following error:

// Warning: (Mayatomr.Geometry) : Suit1:ZBrushPolyMesh3DShape: subdivision surface does not support separate displace approximation, ignored. Tune primary tessellation / approximation for displacement.

From what I understand, it happens when the Feature Displacement is turned on… but it’s turned off :confused:

Thank you !

#4

Amidar, I use Maya and tested displacement maps last night. i was using Renderman for Maya and what I noticed is that I had to use alpha gain and alpha offset values that were REALLY low, much lower than i have ever seen in a tutorial. For instance, I got the best results (with some seams) using values of .05 and -.025. When I kept that ratio the same but went with higher values my model exploded. when that ratio was off (the second number too high) I got the puffy look. Something else I noticed that made a big difference. I used the soften normal edge command on the level 1 mesh. When I didn’t do this I got a model that looked like it had broken apart at the seams. I am going to try the suggestion of using a morph target to maintain the original level 1 mesh to try and remove the last hint of seams.

hopefully that helps.

#5

Well, I did figure out I need much lower numbers and mentioned it on a previous post… :slight_smile:
I’m still looking to fix that last error I’m having.

Thanks for trying to help out !