XeNTaX

I'm trying to reverse-engineer the textures for Just Dance 2018 (which runs on the 2015 engine), and I've seen that the header is "SDD". Intrestingly enough, that's DDS backwards and the text before it is the same as used with Just Dance 2017 (PC). Despite this, changing SDD to DDS and opening it in paint.net didn't work.
Does anyone know what the SDD header is?

Here's a sample: checkmyfriend_po.png.ckd