DDS Files

DDS is the file extension used to denote the Microsoft DirectDraw Surface (.dds) texture file format.

Oblivion employs the DDS format for textures. The Microsoft DirectDraw Surface (.dds) file format stores textures and cubic environment maps, with or without mipmaps. It was introduced with DirectX 7.0.

Although the format is not natively supported by most graphic editing applications, there are a number of Tools designed to handle the format.

DDS Settings used by Oblivion

Usage	Save Format	Mip Maps	Image Type	Use of Alpha Channel
Textures without Transparency (Most Models and all Landscape)	DXT1, RGB	Yes	Color map	Alpha channel not available
Textures with optional Transparency (Needs to be activated in NIF-File)	DXT3, DXT5 ARGB	Yes	Color map	Transparency (Black = Invisible, White = Opaque)
Textures with Parallax displacement mapping (must be activated in NIF file)	DXT3, DXT5 ARGB	Yes	Color map	Displacement mapping (Black = recessed, White = raised, 50% gray = baseline)
Normal Maps (*_n.dds)	DXT3, DXT5 ARGB	Yes	Tangent Space	Specular shine (Black = no shine, White = high shine) Glossiness is controlled through a mesh's NiMaterialProperty in the NIF file
Glow Maps (*_g.dds)	DXT1 RGB	Yes	Color map	-
Icons (And other GUI elements)	DXT3 ARGB	No	Color map	Transparency in GUI (e.g. Weapon Icons)
BookArt	DXT3 ARGB	No	Color map	Transparency on Page (Show Book's Background Texture)
Loading Screens	DXT5 RGB	No	Color map	-

NOTES: Normal Maps don't necessarily need to be saved as DXT3, you can save a normal map as DXT1 No Alpha if you don't need the alpha channel. This will give you a smaller file, with no gloss effect whatsoever though.

DXT5 can also function as a normal map format. DXT3 uses an Explicit alpha map, which has a noticeable step in the grayscale gradients of the map. DXT5 uses an Interpolated alpha map, which does not have this step and may be better suited for some situations.

Though parallax and transparency mapping can function at the same time, the formats in which the alpha channel must be configured for the two effects is usually incompatible and may produce unwanted effects.

Oblivion can also use uncompressed texture files, specifically 8.8.8.8 Unsigned format. This completely eliminates compression artifacts not pre-existing, but is significantly larger in file size (and thus harder on the video RAM resources).

See Also

DDS Tools
DXTn Info @Wikipedia