I am not sure, so I will let you view some tutorials on Masks
http://forum.cyberlink.com/forum/posts/list/30026.page
Scroll to the Heading
MASKS
I suspect that the term you are using does not exactly apply to Powerdirector.
I am sure that Powerdirector does have the capability of producing the effect you are looking for, just not in the way you expect.
One description I read of what a garbage matte is, says it is a background image that the actors appear to be in a Area defined by the Matte.
One method in Powerdirector is through the use of Chroma Key, You film the actors on a solid green background then place the background image behind the actors in Powerdirector.
Masks can be used to insure the actors do not go outside their area.
Carl312: Windows 10 64-bit 8 GB RAM,AMD Phenom II X4 965 3.4 GHz,ATI Radeon HD 5770 1GB,240GB SSD,two 1TB HDs.