Reverse Motion Keyer?
 

Hey Guys,

I've got a static shot here with two people entering the frame from the left and right, meeting in the middle.

For some reason i'd like to replace the background of the shot with a graveyard. In my search for a way to do this without painfully masking the people by hand I've found the BCC Motion Key plugin which can remove moving objects from a frame. It works really well.

So i am wondering: if bcc motion key can detect what moves and removes it - is there a way to keep whats moving and remove all the background?

Thanks :)

Hi Daniel. In Effects/Keying there is the Difference Key which is designed for that - though it has variable results especially if there are shadows. If you are getting a clean key from BCC Motion Key (sorry I have never used it) and it creates masks around the moving figures you might be able to go into the mask properties and iether invert them or set them to 'subtract'?

Sorry about the double post but can't figure how to delete this?

that was sort of obvious. now i really feel stupid ;)

thanks for the idea!

Daniel or anyone - just out of curiosity does BCC Motion Key create tight masks of only the moving object? I checked out their site but it doesn't say much and, let's face it, anything that might save rotoing is worth knowing about.

unfortunately there is no 'show mask' option :(

If BCC Motion Key is delivering a clean background, then do this:

1) Put your original shot through BCC Motion Key
2) You now have a "clean" background with no people in it
3) Put the clean background in your project
4) put the original footage in a new layer over the clean background
5) Apply a difference key - this should give you a nice mask with only the shapes of the moving people
6) Use that mask to key out only the people and drop everything on top of your graveyard scene

Thanks. Great Guide!