What are normals?

Normal mapping, as discussed in a previous post, is a way of applying normal information from a high poly mesh to a low poly mesh, to give it more detail. But what are normals? How do they work?

Normals, or surface normals, simply put are the direction that the surface faces. Each side of a cube has a unique normal, as they all face in different directions. Since high poly models are much more detailed than low poly models, their have much richer normal information. By seeing where this normal information differs, 3D modeling software can figure out where to apply new normals to a surface (even if it is not it’s natural, default normal), and where to leave it the same. While this does not affect the actual shape of the model, it will affect the way light reacts when hitting that model, since the way it’s faces are pointing, or sections of its faces are pointing, has been changed by the normal map in the computers eye.