The favorite texture format the .dds (DirectDraw Surface); it can be uncompressed or compressed with or without alpha.
Some part of the material texture are just free files:
| X | diffuse |
| X_n | normal |
| X_nh | normal (rbg) + displacement (in the alpha channel) |
| X_spec | specular |
Other needs .nif model edit, the name is then freeform. But usually are called as the first column.
| X_ao | detail map in the nif |
| X_glow | glow map in the nif |
Uncompressed: $ convert input.png -define 'dds:compression=none' output.dds
Compressed without alpha: $ convert input.png -define 'dds:compression=dx1' output.dds
Compressed with alpha: $ convert input.png -define 'dds:compression=dx5' output.dds
To make the nh we need to combine normal and displacement, one can do:
convert normal.png displacement.png -compose copy-opacity -composite 'dds:compression=dx5' output_nh.dds
One has to be sure that displacement.png is grayscale mode without alpha channel.