Dynamic Levels of Subdivision

From ZBrush Info

Subdivision modeling is probably familiar to most users of modeling programs; it increases the polygon count of a model by replacing each polygon with multiple polygons.

In ZBrush, a Polymesh retains a "subdivision history." To put it another way, each time a polymesh is subdivided, the geometry from the previous polymesh is remembered, all the way back to the original polymesh. So a subdivided mesh can have multiple levels of subdivision.

You can move back and forth between these subdivision levels as you model; if you need to make 'large-scale' changes to an object, such as raising a significant portion of the surface, you can do it at a lower subdivision level where the model's polygons are relatively large (more of a 'cage') while fine details can be sculpted at a high subdivision level. In either case, changes will be propagated across all levels, so sculpting geometry at one level does not lose the work you've done at another level. Some example uses of Resolution Levels follows:

• At the first resolution level of your model you will be able to sculpt general forms and establish the model’s overall gesture. You will not be able to sculpt toe nails or wrinkles.
• At a resolution level of, say, 3 an artist may be able to begin developing more specific forms such as the eye muscles or the individual lips.
• At a resolution level of, say, 5 the artist should be able to begin developing forms such as the crease of the upper eye lid or wrinkles.

Subdivision levels are also used to generate bump, displacement, and normal maps. Detail is added to an object at a very high subdivision level (possibly with many millions of polygons). That detail can then be compared against a lower subdivision version of the same model to generate a displacement or similar map. Once generated, that map can be taken to an external program and applied to the lower-poly-count model to give a detail effect almost indistinguishable from the high-level sculpting in ZBrush.

Working With Dynamic Levels of Resolution

Let’s look at the settings in the Geometry sub-menu of the Tool palette. It is important to note that our options for the PolyMesh are different than the Sphere3D from the Sculpting Basics guide. This is because Sphere3D is a ZBrush primitive which is a special ZBrush geometry format. In order to use MRME you will have to start with a base mesh or with ZSpheres.

To add levels of resolution to you model go to Tool:Geometry:Divide. If you save your model now as a .ZTL (Tool:Save As) it will keep these levels of resolution.

When you divide your model you can divide it smoothed (Smt on) or unsmoothed (Smt off). You can also smooth its UVs (Suv).

• For character work, you will most likely divide the model with smooth on (Smt) but with smooth UVs (Suv) off
• For more mechanical objects or architectural facades you will want to Divide the model with Smt off. This will add the necessary geometry without altering the form

To go up and down the levels of resolution you can use the slider, press the Lower Res or Higher Res button, or use the hotkeys: “D” goes up, Shift + “D” goes down.

ZBrush uses the Catmull-Clark subdivision algorithm to divide a model. If you are bringing in a broken model where the head is separated from the neck it will shrink the edges of each part inwards.

To address this, in your Tools:Geometry sub-menu press the Crease button. This will lock down the edge of each separate piece of geometry. To remove a crease, press Uncrease.

Wherever possible, however, you will want to combine and merge verticies before bringing the model into ZBrush. Consider having a separate model that is just for sculpting in ZBrush.