Editing Normal mapping (section)

==Spaces==

The orientation of coordinate axes differs depending on the [[Vector_Space | space ]] in which the normal map was encoded.
A straightforward implementation encodes normals in object space so that the red, green, and blue components correspond directly with the X, Y, and Z coordinates.
In object space, the coordinate system is constant. 

However, object-space normal maps cannot be easily reused on multiple models, as the orientation of the surfaces differs.
Since color texture maps can be reused freely, and normal maps tend to correspond with a particular texture map, 
it is desirable for artists that normal maps have the same property.
[[File:NormalMaps.png|200px|thumb| A texture map (left). The corresponding normal map in tangent space (center). The normal map applied to a sphere in object space (right). ]]

Normal map reuse is made possible by encoding maps in [[tangent space]].
The tangent space is a [[Vector_Space | vector space]], which is tangent to the model's surface.
The coordinate system varies smoothly (based on the derivatives of position with respect to texture coordinates) across the surface.

[[Image:Image Tangent-plane.svg|thumb|A pictorial representation of the [[tangent space]] of a single point <math> x </math> on a [[sphere]]]]

Tangent space normal maps can be identified by their dominant purple color, corresponding to a vector facing directly out from the surface. See [[#Calculation | Calculation]].