ZBrush Character Creation - Advanced Digital Sculpting 2nd Edition

80 chapter 3 ■ Designing a Character Bust

ZBrush and Working with Imported Meshes

In ZBrush, models are 3D meshes that are imported into ZBrush to become ZTools. The

difference between ZTools and models is that a model is just a 3D mesh file that contains

polygons and UV information. A ZTool is ZBrush’s native file format for sculpted objects. A

ZTool can contain multiple levels of subdivision, high-resolution sculpting details, texture,

and polypaint information, as well as alpha maps and layer data. The ZTool format allows

you to store far more than just an OBJ file.

Models are imported into the Tool palette where they become available with the other

ZTools listed there. When importing models into the Tool palette, it is important to be sure

your mesh is optimized for detailing in ZBrush. If your mesh is ordered and animation ready,

or is part of an existing production pipeline, you may not have the freedom to lower the ini-

tial polygon count. The edge flows and topology have already been approved for rigging and

animation. When loading a model into ZBrush, you must understand how ZBrush deter-

mines subdivisions levels and where the system limits are.

Physical memory is the most important deciding factor in determining your highest

subdivision level, followed closely by processor speed. ZBrush is not concerned with graph-

ics cards, and multiple processors are only useful when moving the model around the screen

and sculpting. ZBrush uses the amount of physical RAM installed on the system to deter-

mine the highest possible subdivision level attainable. The processor comes into play when

you start to rotate and manipulate the sculpture onscreen. A faster processor will allow you

to move more polygons with less lag.

You can find the maximum subdivision level that ZBrush has set for the machine by

choosing Preferences → Mem. The MaxPolyPerMesh slider will show the value in terms of

millions. A value of 20 here means that ZBrush will only allow you to subdivide to 20 mil-

lion polygons (Figure 3.1). As shown in Chapter 1, “Sculpting, from Traditional to Digital,”

it is possible to raise this value, but it is not always recommended as it can cause instability. If

you raise the MaxPolyPerMesh value slider, be sure to raise the CompactMem slider to 256,

2048, or 4096. Doing so increases the amount of memory ZBrush will use before starting to

write temp files to the hard drive, which slows down performance.

The question arises of how to ensure you get the maximum subdivision levels from

ZBrush. Often an artist will load a mesh for sculpting only to find that it subdivides to a

level that is unsatisfactory to get the level of detail desired. Starting with a lower polygon

count can help ensure you reach the highest possible subdivision level. This approach works

because of the algorithm ZBrush uses to subdivide.

ZBrush uses Catmull–Clark subdivision each time you click the Divide button. This means

that for each subdivision level, ZBrush multiplies the total polygon count by 4. So if level 1

is 4,000 faces, level 2 will be 4,000 x 4. That gives you a level 2 poly count of 16,000. If this

mesh were divided again, ZBrush would multiply 16,000 by 4, giving you a level 3 polygon

count of 64,000. If your initial poly count at level 1 were 17,000, you would reach 1 million

faces by three subdivisions. Unless you set your MaxPolyPerMesh slider to something above

4, you would not subdivide again as the fourth subdivision level would be over 4 million.

Underlying topology can become a concern in ZBrush if your edge loops define forms

that you choose to change later. There are times where your topology may fight the forms you

are trying to make. Because of this, simple block models can be beneficial when working in

ZBrush. They offer extremely simple bases that can be moved at the lower subdivision levels

Figure 3.1 The
Mem preferences