It's more about how DDS works, textures are required to be power of two (2^X), e.g. 8x8 pixels, 16x16, 32x32, 64x64, 128x128, 256x256, 512x512, 1024x1024, and so on.
I recommend to use DDS plugin mentioned

which is easier, you could be able to select uncompressed format, or just going with standart DXT5.
DDJ is the same format but with some extra bytes from Joymax, just to assert dominance.