What is the most optimal way to create a "clipping" Grade layer that uses Set Matte and a Mask
You're probably familiar with the way of mask clipping in Photoshop. This makes a layer to be applied only within the boundaries of the base layer. You can apply masks to the clipped layer too. This is what I want to make in HitFilm.
The case is the following: I have two people filmed on a green screen, masked out and placed on a background. One of them has to cast shadow over a smaller area of the other one. Keep in mind I have about 15 layers with people, so the solution has to be as economic as possible. What I initially did was to create a Grade layer having:
1) Set Matte (with the layer of the person that will receive the shadow) with an Alpha mode (the person is a layer with a transparent background).
2) Levels Histogram or Curves that will create the shadow
+ a mask on that Grade layer that will limit the shadow only to a portion of the person.
Of course, that doesn't work as intended, because the Grade layer + Set Matte (with an Alpha matte) creates a black background outside the person's silhouette. The only workarounds I had were:
1) To use a blending mode on the Grade layer that will remove the black background. The problem is it will affect the way the shadow looks as colors and contrast and I have to fight with it to make it look as if the blending mode were "Normal"
2) To duplicate the person layer, add the shadow and a mask to constrain it over a certain area. The problem here is that if I make changes in the original layer (such as tweaking the exposure or the colors) I have to remember to always copy the settings over the shadow layer. This makes the rendering way slower too. This is why I prefer the 1st workaround although it's not perfect either.
Is there a way to do that with my initial intent and approach, but maybe I am missing a minute detail?