Until now we have almost exclusively treated Phong shading. An additional way
to add more realism to a rendered scene is to use bump mapping. It
allows to increase the visual detail of a scene without requiring excessive
amounts of geometric detail. It is a technique that was invented by Blinn
[3] to add roughness or wrinkles to a smooth surface. It does not
change the underlying geometry of the model, but fools the shading to produce
an interesting surface by using a perturbed surface normal
read from a normal map (Figure 7(a)). Bump mapping is a
very efficient approach because it decouples the texture-based description of
small-scale surface irregularities used for per-pixel lighting computations
from the vertex-based description of large-scale object shape required for
efficient transformation, rasterization and hidden surface removal
[10].