ok i will put the options forward without confusing.
tga is a name of a graphics file that draws on your in game objects.
dds is another name of a graphics file that draws on your in game objects.
both do the same job but tga does not work on x10, but dds does, this is because they are filed differently.
e.g. a nintendo ds will not play a game made for play station 3.
so you have to upload the tga picture on a program that will read tga files and that will translate into another format in this case dds.
so the programs that will do this is
dds converter.
paint.net
and gimp.
the first 2 are the easiest.
paint.net: just load in the picture, then once its loaded go to save menu, select save option, at the bottom of the opened window, open the browse part which will give multiple file options, select dds then save, and thats it.
in your files will be two files, one dds and one tga.
suggest erasing tga file.
hope that helps
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