I was never happy with the normal map on my El 18 mod in TPF after I converted the TGA file to DDS. I thought it looked weird, as if the green channel was flipped (the difference between DirectX and OpenGL), but it didn't work out. And it would be strange if it had worked, because the project in Substance Painter was created and exported with normal map for OpenGL too.
So here's some comparisons.
This is the DDS profile I use to convert in Photoshop. I have tested different settings in the Image Options and Normal Map Settings, but they don't seem to do any difference.
This is the normal map as TGA. It's great! The correct parts look like they bulge OUT, and the highlight is at the TOP of the shape.
This is how it looks as DDS. Notice how the highlight is at the right side, and makes it look like it's going IN.
Here I have flipped the green channel - a little better - but not correct. It's sort of an illusion that it goes out - it's not going in either. Totally useless.
How do you guys deal with this? It will obviously add to the load time and download size if I need to use TGA, but it obviously looks the best. Do you even use DDS for the normal map at all?