ZBrush Character Creation - Advanced Digital Sculpting 2nd Edition

■ Cavity and Ambient Occlusion Maps 339

Most of this chapter has been concerned with exporting maps from ZBrush that help re-
create the look of the detailed model in an outside program. Decimation Master is unique in
that it allows you to selectively reduce or decimate the ZTool so you retain the fine details but
with fewer polygon faces. This is accomplished by triangulating the mesh to varying degrees
along the surface of the model. You can use Decimation Master to export your ZTools with
color information as OBJ files to be rendered in 3D programs. You can also use this plug-in
to prepare models for 3D print. Most 3D printers have a file size limit on the data you try to
print. Using Decimation Master allows you to create 3D models that will not only retain their
surface details but will also be suitable for printing on a rapid prototype machine.
In this section you’ll learn how to take a highly detailed creature bust and decimate it
to under a million polygons while retaining the color information as well as surface details.

1. Load the alien head ZTool from the DVD. Step down to the lowest subdivision level
   and generate AUV or any other suitable UV mapping for the head.


2. Step up to the highest subdivision level and generate a texture map from the polypaint
   data by clicking Tool → Texture Map → New From Polypaint. Clone and export the
   map as explained in Chapter 5.


3. Open the ZPlugin → Decimation Master menu. Enable Keep UVs so the map you
   created will still work on the decimated model. If you were merely exporting for 3D
   print, you could disable Keep UVs.


4. Since you are working with only one subtool, click Preprocess Current. If you want to
   process multiple subtools at once, you can click Preprocess All at this stage. ZBrush
   will now process the highest subdivision level mesh, writing a cache file to help it deci-
   mate the mesh to a specified polygon count.


5. Once the preprocess is finished, set the percentage of decimation or a target poly
   count. The k Polys sliders is in 100,000 polygons, so 200 is actually 200,000 trian-
   gles. Set this slider to 900 for a resulting 900,000 triangle mesh. Now click Decimate
   Current to complete the process. Figure 9.82 shows the original ZTool beside the deci-
   mated version. Figure 9.83 shows the decimated model with the texture map applied,
   displayed in the Maya viewport ready for rendering.
   You can get exceptional results rendering decimated meshes in Maya and bypassing
   the need for normal, bump, and displacement maps altogether. Figure 9.84 shows a frame
   from a turntable rotation I rendered using the decimated head from this section. See the
   DVD for this Maya scene file to render on your own—it is called highResAlienRender.mb.

16 million polys 800,000 polys Maya render of decimated head

Figure 9.82 The original ZTool and the decimated version on the right