TGA files are used for some of the graphics in NWN. It is a uncompressed format which means no quality loss but a huge amount of speed and huge files when the image dimensions are even moderately big.
It has the lowest priority of texture formats usually, outranked by PLT then DDS (ie filename.dds will load over filename.plt which loads over filename.tga) but if you have the same DDS and TGA file at the same "level" the TGA loads first - see Content Load Order for more information.
NWN supports 32bit TGA files with alpha. They must be powers of 2, such as 32x32 or 128x1024. They can be uncompressed or compressed with RLE compression (using Bottom Left, not sure about Top Left). GIMP for instance can output compressed RLE which is up to half the size for some icons/textures.
For anything other than game icons (GUI icons, feats, spells, scrolls, and items) it is highly recommended to use DDS instead.
| Image Dimensions | Uncompressed TGA File Size | Notes |
|---|---|---|
| 32x32 | 4KB | Game's default (now awful) icon size (eg; feats, spells) |
| 64x64 | 16KB | |
| 128x128 | 64KB | |
| 256x256 | 256KB | Maximum limit of certain shiny water effects. Retaining TGA for this might be advisable to improve quality slightly. |
| 512x512 | 1MB | |
| 1024x1024 | 4MB | |
| 2048x2048 | 12MB |
The TGA file format was used by Bioware to retain quality and compatibility due to the very early introduction of DDS. Therefore it got used for a large portion of the original game files. Once Hordes of the Underdark came around most usual textures were made in DDS only.
Due to qwirks with the game engine this is a list of suitable uses of TGA:
DDS should be used for most everything else.
See also Textures for a full use case breakdown between formats.