This is the entire process for generating normal maps from
modeled geometry. It does have its quirks, but once you learn
those, the process is amazingly simple. With a little practice,
generating normal maps will become second nature to you. To
truly understand normal map creation, however, you need to
understand how they work.
How Normal Maps Fake Detail
Before we talk about normal maps specifically, we first must
talk about surface normals. A surface normal is the vector, or
ray, that represents which direction the polygon is facing. This
normal adjusts how light “bounces” off of that surface. Every
vertex stores the normal information for all of its neighboring
polygons. When a polygon shares a smoothing group with a
neighboring polygon, the normals on the shared vertex are
averaged together. This gives the surface a smooth look as it
transitions between the different surface normals.
392 Chapter 19
Figure 19-4:
The final result
after projecting
the detail
.
Note:
If you want to look at the normals of the surfaces in the
models you’ve created, just apply the Edit Normals
modifier. This modifier not only allows you to look at
them, but also to average any normal you like. It’s not a
tool you’ll use every day, but you may find a use that
many have not thought of.
The key to how a normal map accomplishes this effect is in its
name. In the most common use of normal maps, called “tan-
gent space normal maps,” the texture map literally modifies
the surface normal on a per-pixel basis. That is, each pixel on
the texture stores a value to adjust how the light reacts to it.
That sounds like it would take a long time to render, does it
not? Well, not nearly as long as rendering and tracking a
model with 3 or 4 million polygons!
Here’s how the normal map itself stores that data.
Figure 19-6 shows what you get when you render out a
normal map. (To see the following images in color, go to
http://www.wordware.com/files/3dsmax2008 and download
the companion files.)
Normal Maps 393
Figure 19-5: No smoothing groups vs. smoothing groups
with normals shown
This normal map is pretty standard. Overall it’s a purplish-
blue color with some bits of red and green in it. All of these
colors actually are normal vector information stored in red,
green, and blue (RGB) format. Let’s break it down a bit more.
An image is made up of multiple channels of red, green, blue,
and an extra alpha layer that represents transparency most of
the time. Each of these channels is like a black and white
image. Put them all together and you get your final image.
However, in a normal map these channels store data.
The red channel represents the details captured on the
x-axis.
As you can see, the red channel appears to be the high-poly
model lit from the right. All of the surface’s polygons that are
394 Chapter 19
Figure 19-6:
The normal
map used
above
Figure 19-7:
The red channel
singled out
straight up like the low-poly surface will appear as a 50% gray.
The surfaces facing 90 degrees to the right in relation to the
low-poly surface will be white, and surfaces facing 90 degrees
to the left will be black.
If it looks like the image is lit from the left, your eyes are
playing tricks on you. Imagine that the image is actually 3D.
Anything sticking out of the image is going to be lit on the
right-hand side. Anything sinking into the image is going to
appear to be lit from the left (however, this is just because it’s
sinking in instead of jutting out). Some of this is caused by
there not being any shadows cast on the image. Traditionally
you would have a shadow where the surface sinks in and your
brain would tell you “Hey, that’s going in, not out.” This isn’t
the case with normal maps, however, because they aren’t
there to cast shadows.
Similar to the red channel, the green channel is storing all
the data in the y-axis. It appears as if it’s lit from the bottom.
Finally, we have the blue channel. So many people are con-
fused by the blue channel and some are under the impression
that it does nothing. This is simply not true! The blue channel
represents the surface facing the same direction as the
low-poly model. It appears as if you are looking at the surface
while lighting it from straight on. This gives the effect of any-
thing flat being white and any surface starting to face farther
Normal Maps 395
Figure 19-8:
The green
channel singled
out

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