Adding/combining masks together? I am working on a Stop-Motion Project and am using Blender 2.8 to add green-screening effects via masking using the nodes.  In the image, the green screen has a similar shade of green to Doc-Ock, and have created a mask to prevent the shades from clashing.  The top mask been successfully combined with a powerpoint image, however I am have trouble adding the inverse of the mask to the image.  I am using Alpha Over, and the line that was used to create the mask is showing/cutting-out.  Is there a way to seamlessly combine the two masks?  I have tried using Add and Subtract via the Mix Node to no avail.  Any suggestions are appreciated!
Masks can be combined as images. Use a color mix node and add (or subract) different masks. In this example a couple of garbage mattes have been combined to be used by a single keying node.



Or you can combine the resulting image with others that have an alpha channel already using alpha over.



Or combine the alpha channels separately and associate them later using the set alpha node.