Normal Maps

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Normal Maps
Normal maps are textures that are used by Oblivion's render engine to give a model surface an appearance of additional surface detail. In its effect it is very similar to bump-mapping. The normal map is used in shading the model and provides a convincing relief effect to surfaces, making the model look like it has a much higher polygon-count than it actually does. For Oblivion, normal maps are DDS textures indicated by an _n suffix after the texture's base name. Basically, a normal map tells the game engine how light should reflect off an object.
Oblivion uses Tangent Space normal maps, best recognized by the blue color that fills any 'flat' areas of the image.
There are many different ways to create a normal map, either from a 2d image, a 'height map', by transferring data from a High-Poly mesh to the Low-Poly mesh, or a combination of the above. A common practice is to create a hybrid version of the color map (texture), whereby the artist removes/adds detail in the image to produce an image that will convert well into a normal map.
Also, the Alpha Channel of the normal map contains the Specular Map, which controls how reflective/shiny the overall effect will be.
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