Surfacing - Blender Foundations: The Essential Guide to Learning Blender 2.6 - page 175

In this case, careful observation will show that gypsum (or plaster) walls don't show a lot of variation in
color. They are generally painted white. So, we'll let the texture affect the diffuse color only slightly, say,
0.200.
If you're creating the example for yourself as you follow along with the topic, you may have noticed
something odd when you enabled the Color control. The material preview turned a nasty magenta color.
This is because the stucci texture (as well as most of the other procedurals) does not generate color infor-
mation by default. You can force it to generate color by use of the Ramp option as discussed earlier, but
for now it is only a gray value. When the Influence panel receives noncolor information for a channel
that requires color, it has to generate one. The color picker swatch at the bottom of the panel lets you
set this color. For the wall example, I've set mine to a yellow gold a shade or two darker than the main
diffuse color of the material.
With a little variation in color, let's move on to shininess, which is varied with specular intensity. Enable
the Intensity option in the Specular section of controls. The main Specular value for this material is set
around 0.15, and enabling this seems to blast it back out, which you can see in a sphere material preview.
This is because texture influence adds to whatever the original value is in the material panel. So, an original
Specular Intensity of 0.15 plus full (1.00) intensity from the texture panel generates a value over 100%.
That's not what we want at all. Ideally, we'd like to just have the texture intensity completely substitute
for the material value. Reducing the material's Specular Intensity to 0.0 does the trick. Now, whatever
value we get from the texture is added to 0.0, which is just the same as pretending that the material value
doesn't even exist.
So, the maximum Specular Intensity from the texture is 1.0 at the moment. We want to retain our original
limit of 0.15, so simply reducing the slider to 0.15 gets us to where we need to be. When working with
single values like this (Alpha, Mirror, etc.) in the future, the rule is: Reduce the material value to 0.0, and
set the texture-based value to the maximum you would have used in the material.
Finally, let's look at the roughness of the wall. A gypsum wall, although often smooth, is not a mirror. It
has some roughness to it that you can feel—sometimes more or less depending on the decor. This rough-
ness can be simulated with the Normal value in the Geometry section. Applying a texture to a surface's
normal value is a rendering trick that lets us pretend there is more complexity to the geometry than actu-
ally exists. The “normal” we're talking about just means “which way the surface is pointing.” Figure 7.9
shows two renders of a simple quadrangle. The one on the top has normals all pointing in the same direc-
tion. The one on the bottom has a texture applied to its normal channel. The texture is used by the
renderer to vary the actual normal, giving the illusion that there's a lot going on, when in fact it's just the
same old quadrangle as the one in the first image. To actually model that kind of surface detail on a mesh
would take a ridiculous amount of time, both to construct and to render.
The Normal value defaults to 1.0. This affects the apparent “depth” of the roughness introduced by the
texture. It's usually more efficient to just test-render and adjust to get the value correct, rather than trying
to do some kind of funky math involving texture space sizes, geometry, and texture values. Keep in mind
the principle of subtlety, though. You may have spent an hour getting all the aspects of your texture just
right, but that doesn't mean you need to beat your viewer over the head with your triumph. How much