ZBrushCentral

zBrush and subdivision smoothing

ZBrush Usage Questions
#1

Hello,

I have a question regarding the smoothing of subdivision in zBrush.

If I import Suzsanne from Blender to zBrush it looks like it should look:

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I can reconstruct the subdiv and switch between the subdivision levels. Everything looks fine, like here, the lowest reconstructed subdivision level:

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But if I delete from the lowest subdivision level the higher level sand subdive again things get off.

The highest one lost a noticeable amount of volume, compared to the original:

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and also the lowest level seems to be affected:

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This seems somehow related to zBrush SMT (Sudivide Smooth Modifier).

Is it in zBrush somehow possible to smooth in a way that it will match to the Subdivision of Blender?

#2

Hello @Rincewind3D ,

The details on all the subdivision levels inform the others. If you delete your high res details and then re-subdivide youre forcing the program to re-calculate the model without any of that information. This will result in the form shifting.

Lower resolution geometry can be reconstructed from a high resolution mesh. Higher resolution detail however cannot be reconstructed from a lower resolution mesh. Once it is lost, it is gone.

You must always maintain at least the level of subdivision that you need to match from program to program. That geometry needs to remain untouched and unchanged if you need the files to match. So if you’re working on the mesh at subdivision level 4 in the external program, you also need to retain that same level of subdivision in ZBrush.

You can delete the lower levels of subdivision and it will remain the same mesh at that level of subdivision. If you delete the higher detail and subdivide again, it is now a different mesh.

:slight_smile:

#3

I should also mention that the very act of subdividing a mesh subtly alters the form at all levels of subdivision. This is an unavoidable aspect of the subdivision smoothing process. So if you were working on a mesh at subdivision level 4 in ZBrush, exported that to the external program and then subdivide the mesh again in ZBrush, that same subdivision level 4 may no longer exactly match the subdivision level 4 you exported.

This is why your geometry should be mostly stable and not expected to change by the time you reach a point in your workflow where you need files to match between programs.

#4

After analyzing the whole situation more, I really think zBrush needs to improve the subdivision algorithmen.

I figured out that reconstructionist subdivisions also have in other 3d apps the same behavior as in ZBrush.

But zBrush behaves strangely when you subdivide a base mesh.
While other apps keep the base shape when you subdivide, zBrush smoothes the also the base shape.

This is a well-known problem in ZBrush. There are workarounds like

(this macro is also available at Ryan's Tools: Zbrush Plugin ).

But this workaround has still one big downside. Let’s assume I want to create a custom shape for a DAZ Genesis figure with HD details for DAZ Studio or Blender.
If I use the ZBrush subdivision I destroy the base shape, which is bad for the base shape morphs I sculpt.
If I use the macro von Ryan, I can keep the base shape. but the higher level subdived mesh is bloated.

To get an accurate behavior with external 3d apps we need a feature where ZBrush doesn’t smooth the base shape, but from subdivision 2+ on it should behave like now.
Best way would be to make subdivision as some kind of modifier, which an be enabled and disabled. If you are disabling zBrush subdivision, you are getting back the original unsmoothed mesh, but with all sculpted basemesh changes you did when subdivision was enabled.