don't know, you will have to check the TGA file format. But i compared the first 18 bytes of both a compressed and an uncompressed 16bit TGA file, and they are the same except for byte 2:
compressed TGA header:
00 00 0A 00 00 00 00 00 00 00 00 00 5F 00 9F 01 10 00
uncompressed:
00 00 02 00 00 00 00 00 00 00 00 00 5F 00 9F 01 10 00
of course, form the same image.
cryo