The "add" node also works but has its own limitations.

You can not get "more" white then true WHITE.

And you can not get darker then true BLACK.

There is nothing less then RGB 0,0,0 and nothing more then RGB 256,256,256

You will have to think about that when building both maps.

Poser 1, 2, 3, 4, 5, 7, P8 and PPro2010, P9 and PP2012, P10 and PP2014 Game Dev
"Do not drive faster then your angel can fly"!