I've implemented normal maps into my game renderer using the formulas by Christian Schuler.
It works OK with most normal maps but some not so much since in some the Y component (green) is reversed. Apparently there is no real standard here and Maya does it one way and Max does it the other way.
I'd like to be able to look at a normal map's values and somehow determine which scheme is being used, if that's possible.
Also, though I have not actually seen any, some normal maps appear to use only two channels and the third channel is left blank and calculated at runtime. Ideally I would be able to detect those, too. I figure maybe the Z channel is all zeros? I am not sure that would save any space though so maybe it is some other scheme.
Seems like an obvious desire, but I don't see any references to this. but then, maybe it's not really possible.