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	-
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: Compression for the RGB channels does not differ between DXT1, 3, and 5. The differences lie in the manner in which the alpha channel is compressed. DXT1 compresses the alpha map as all-white, which is highly compressible. DXT2 has a two-bit alpha channel, either white or black. DXT3 has a larger grayscale available ("Explicit"), and DXT5 has as wide an alpha map grayscale as it has for the color channels ("Interpolated").

Because of this, saving a Normal map as DXT1 has the unwanted side effect of causing full specular highlighting over the whole mesh to which the texture is assigned to. DXT3 or DXT5 are strongly recommended for normal maps.

Though both DXT3 and DXT5 have alpha channels that can function as specular maps, DXT3 has a noticeable step in the gradients; DXT5's more gradual gradient may be better suited to 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