How to limit chromakey to specific area of clip?

TeetimeNC wrote on 12/21/2007, 12:51 PM
I have some footage with sky, fairly clean horizon, and foreground. I want to replace the sky. There is a lot of the sky color in the foreground, but the foreground and sky are well separated by the horizon. I can key out the sky using chromakey, but it also gets the similarly colored foreground. What is the best way to limit the area the chromakey is applied to? I was trying use a bezier mask to hide the foreground from the chromakey filter but wasn't able to come up with the right combination.

Thx,
Jerry

Comments

jetdv wrote on 12/21/2007, 1:10 PM
Here's at least a couple of ways:

1) Use keyframes on the chromakey plugin timeline to turn it on and off at the proper times.

2) Split out the section you want this to apply to and only apply it to that small section.
TeetimeNC wrote on 12/21/2007, 2:25 PM
Thanks Ed, but I'm not trying to split it along a time boundary. I am trying to figure out how to not apply chromakey to the lower half of the clip, throughout the entire clip. Sorry that I wasn't clear on that.

Jerry
Soniclight wrote on 12/21/2007, 2:36 PM
How about stacking two sets of the segment clip where you have this issue and A) use a mask on the top one with chromakey set to "clean out" one color (i.e. sky bleed-through), and B) another mask + chromakey to the bottom clip to clean out or safeguard its colors?

Maybe a dumb idea, but figured I'd toss it in just in case it might work :)
JackW wrote on 12/21/2007, 2:45 PM
How about duplicating the clip on the track above and applying the chromakey there?

Jack
UKAndrewC wrote on 12/21/2007, 3:48 PM
Here's one way:

Track 1: Draw mask around area to keep (or mask) and apply Chroma Key FX
Compositing Mode=Cut
Parent Track Mode= Alpha

Track 2: Child of T1 Copy of event on T1 with no mask or filter
Compositing Mode=Alpha

Track 3: Background to show through Chroma Mask

Andrew
farss wrote on 12/21/2007, 4:05 PM
What you want to create is a Garbage Matte.
You can use a number of tools in Vegas, from the Cookie Cutter to Beziers. Or even 'paint' a B&W matte in PS and use that.

If all the compositing in Vegas baffles you, render out your rough efforts, just worry about the masking in the immediate area of the subject.
Now start new project. Lower track original footage, upper track what you just rendered. Cut away the garbage areas from the upper track. The Bezier mask in Event Pan/Crop is the best but maybe the Cookie Cutter will be enough, you can chain these if needed.

Bob.
TeetimeNC wrote on 12/22/2007, 1:47 PM
Jack, all I can say is duh. Your suggestion led me to the simple solution. I put the original on top of the track above the chromakeyed track and on that top track masked out everything down to the horizon. This let the desired chromakeyed material show through.

Andrew, I tried your technique but couldn't get it to work. This was the type of solution I was expecting, and I was excited when I saw yours because I want to get better at that type of compositing. When I get time I will play more with that and see if I can get it to work - just as a learning exercise.

Bob, I am familar with garbage mattes but more in the context of catching green screen spillage. I'm not yet sure how I would use a garbage matte to handle my situation.

Thanks to all for your ideas.

Jerry