296 chapter 9 ■ Normal Maps, Displacement Maps, Maya, and Decimation Master
corresponding point on the high-res mesh that matches the same point on the low-res mesh.
ZBrush will calculate the differences between a high-res mesh and a low-res surface and
produce a value appropriate for the kind of map being generated. The resulting map can be
used in a third-party renderer to re-create the look of
the highly detailed ZBrush model. ZBrush can create
two kinds of difference maps: displacement maps and
normal maps (Figure 9.1). In this chapter, we’ll focus
on displacement mapping.Displacement Maps
Displacement maps create high-resolution details by
physically displacing the geometry at render time.
The model is sliced into millions of triangles by the
renderer in a process called tessellation. The surface
is then pushed in or out based on a grayscale value in
the displacement map. Some renderers perform sub-
pixel displacement, which is a re-tessellation of the
surface into micropolygons or microtriangles to sup-
port even finer details. The important thing to under-
stand is that displacement mapping requires that the
geometry be heavily tessellated at render time.
Because these maps create actual geometry, they
are heavy on processing power and can involve long
render times. They also offer superior results compared
with any of the other mapping types since the rendered
mesh is extremely dense and carries all the details of
the surface and silhouette. This is in contrast to nor-
mal mapping, which only creates the look of a highly
detailed surface without changing the underlying geom-
etry or polygon count. See Figure 9.2 for an example of
normal mapping versus displacement.
ZBrush also enables you to create bump maps
by using the Bump Viewer material or by generating a
displacement map for use as a bump map. In technical
terms, bump maps and displacement maps are iden-
tical—it is the renderer that reads and displays them
differently. Both are grayscale maps with white values
representing height and dark areas representing depth.
In application, however, bump maps differ from dis-
placement maps in that they do not change the overall
silhouette of the surface. Bump maps give the impres-
sion of surface detail where there is none by perturb-
ing the surface normal of the mapped faces. Because
bump maps don’t require heavy subdivision at render
time, they render much faster than displacement maps
but do not provide high-quality results since the pro-
files are not altered. Bump maps can be extremelyFigure 9.1 A normal map (right) and a displacement
map (left)
Figure 9.2 Two renders of the same character. On the
normal mapping example at the top, notice how the inter-
nal forms appear highly detailed while the silhouettes still
display polygon faceting. The image in the upper right
shows the polygon mesh itself. The displaced render at the
bottom contains all the fine details on the surface as well
as a displaced profile with no faceting.