Key out same pixels

[TheMacB]

i don't know if something like this exists. But it should.

I'm doing a spot with a ghost in it. So I have a lockdown shot with and without the ghost stacked in two video tracks with the ghost on top. I'd like to make the ghost Black and White.

Is there some kind of blending mode or something that i can use so that all the pixels that are the same in both tracks get cut out? so that only the pixels that are different from those on the bottom track remain? i.e. the background gets cut out and the ghost remains.

 

[David Jimerson]

That's what a a difference mask is for. There's a tutorial on vasst.com for just this sort of thing.

 

[TheMacB]

sweet. found tons of stuff about difference masks. thanks david!

 

[Drew Ott]

Couldn't this be used as a green screen then?

I've always been looking for this blending mode. Thanks.

 

[David Jimerson]

A greenscreen is a lot easier.

 

[Drew Ott]

Yeah probably. I don't have room for a green screen anywhere so this might be a decent alternative.

I just dug up an old tutorial on VASST that I saw a while ago when I was just starting Vegas and I never understood on difference masking. It doesn't look nearly as good as a clean chroma key so I can understand why it isn't used much. Plus the tripod has to be locked.

 

[TheMacB]

thanks again david! here's what you helped me do: http://www.dvxuser.com/V6/showthread.php?t=125252

 

[David Jimerson]

That's pretty cool! I'm glad it worked out for you.