You need to work with feathered masks and duplicate layers. Nothing special about it.
Thanks for this fast answer !
Additionnal question : what´s the most efficient way to select in my images (faces mainly) only the brightest parts of my images and grade them independently ?
Thanks again !!
You can apply color range selections using channel effects and of course pretty much any third-party color correction tool has built-in color range features, even the Color Finesse plug-in that comes with AE or Lumetri/ Speedgrade. You really need to research this a bit. There's realyl nothing complicated about it, but you seem to lack knowledge even in some very basich and common AE stuff.