Normal Map

Normal mapping is a texture-based technique used to give the impression of sub-polygon lighting detail, without having to model it. It is controlled by a 'normal' texture, which is used to perturb the surface normal. Since only normals are perturbed, not geometry, it does not affect shadows.

The resolution of the normal map texture is important – you ideally want a one pixel per texel maximum resolution to get the best visual results. Magnifying the texture will blur the results and minifying will lessen the effect with distance.

The output of this shader is a perturbed normal.

Normal Map Example

Here is an example of how a normal map can enhance the lighting detail of simple, flat geometry.

This example shows an un-textured surface, with a diffuse and glossy reflected spherical area light.

Now the same scene but with the normal map applied you can see how dramatically a normal map can increase the lighting detail without paying for the extra polygons.