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, outranked by PLT then DDS (ie filename.dds will load over filename.plt which loads over filename.tga).
NWN supports uncompressed 32bit TGA files with alpha. They must be square (ie powers of 2), such as 32x32 or 128x1024.
These are the sizes with filesize - because TGA is not compressed it gets big, fast. The larger sizes also tend to lag when loading by the engine due to the generation of mipmaps and transfer to the GPU inefficiently. See recommendations below - pretty much don't use TGA!
| Image Dimensions | 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 textures were made in DDS only or original TGA ones were converted to DDS.
It might have at the time retained some quality - especially on tiny 32x32 icons - that DDS would have lost.@~85
Nowadays DDS should be used in 99% of cases. A higher quality DDS file scaled down by the engine or mipmapped to a suitable size is much better looking than the slow loading of a smaller dimension TGA. IE a 256x256 inventory icon in DDS looks and performs better than an 128x128 TGA, especially with the UI scaling nowadays. The fact that 256x256 DDS is 85KB but is 4x the pixels of the 128x128 64GB TGA also helps - a huge increase in pixels at a minimum increase of filesize!
It would be recommended if you did use DDS to include PNG or TGA source files, possibly of a higher resolution then the DDS, in case you need to rescale them later. You can also not load DDS files into the new NUI system so PNG equivalents is a good idea if they will be used in such a way (generally icons).
The only uses that still require TGA:
There may be other things, but well, that needs testing.
See Textures for a full use case breakdown between formats.