Do I understand the function of the Difference Matte (Effects > Key > Difference Matte) in FCP correctly? 1) Take video clip of static scene (a room, for example) and put it on the timeline 2) In a track above the first clip, insert a clip of the same exact scene (shot using a tripod without having moved the camera between clips 1 and 2) with a person walking 3) Apply the Difference Matte key effect to the top clip (the one with the motion that I want to isolate) 4) The result will be that everything that's the same between the two clips will be matted out and I'll be left with only the object(s) that are different between the two clips. This isn't what's happening when I try to apply the difference matte to a pair of clips. I end up with a ghosty image of the person in motion superimposed over the static background. Can someone please set me straight on this? TIA.