Keyframing or not to keyframe with bad green screen issues

[Jeff Kirkland]

Not really. I’d think you either let them drop out of frame or embrace the joys of rotoscoping. Maybe if the image beyond the green screen is dark enough you could do a luma key but that would be a very slim hope.

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Jeff Kirkland | Video Producer & Cinematographer
Hobart, Tasmania | Twitter: @jeffkirkland

[Mark Suszko]

The best technique i’ve found for efficient rotoscoping is to keep cutting the problem in half, every time you set keyframes.

That is, in the example of your footage, I would add the “drawn mask” effect plug-in and set a keyframe at the first frame where the hand begins to touch the boundary between green and no-green. Next, find the last frame you need fixed, keyframe that, adjust the mask. Now go to a spot int he timeline mid-way between those two keyframes, mark the keyframe, adjust the mask.

Now pick a spot half-way between the first point and the middle point. Keyframe and fix that frame. Keep going to a spot half-way between existing pairs of keyframes, setting the keyframe and adjusting the mask. The point of this is to let the software interpolate as much of the job for you as possible, reducing the overall time spent. Once you’ve laid in about ten of these keyframes spots, start playing back and monitoring how well the computer guessed at the changes. Where it went really badly, create a new keyframe there and start sub-dividing the job again. Now you only have to tweak things a little bit here and there, instead of trying to hand- mask every frame.

This is the fastest way I know to do it. There is one other option: content-aware fill. You could try using that to paint-in replacement green by just lassoing the problem area and letting the computer take a whack at it… To help that work, it might require tweaking the overall color and brightness levels to emphasize the differences between foreground and background.