Also known as "
normal vector interpolation shading." It
interpolates the
surface normal, rather than the
intensity. Like
Gouraud shading,
normals are
interpolated from
vertex normals, but also uses
normal and
intensity information that is not located on a
polygon's vertex. This means that it is more
computationally expensive than
Gouraud shading, but yields better results when
intensity and
normal information falls on non-vertex areas of a
polygon.