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Need to key out green screen AND yellow markers as the screen moves into the frame

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Benjamin ReichmanNeed to key out green screen AND yellow markers as the screen moves into the frame
by on Feb 3, 2011 at 5:13:53 pm

I'm more or less a beginner in After Effects, but as part of an editing job, I have to do some keying and it's a bit of a rush, so I could really use your advice.

The video shows a (fictional) game show. There's a scoreboard high on the wall which I have to fill with graphics. It's painted green with yellow tape markers at the corners and in the center.

For most of the shots, nothing ever intersects the scoreboard, so I believe I can ignore the green and just use a four-point tracker set to "Perspective Corner Pin" to tack the graphics over the screen without any keying. I've had some success with that in my limited tests.

There are two issues I don't know how to handle:

1) In the opening shot, a somewhat shaky pan and zoom starts on the gameshow host and then reveals the scoreboard--and the host's head intersects the bottom of the scoreboard. So I need to key out the green of the scoreboard, which I've done successfully. But I also need to get rid of the yellow markers. When I try to key out the yellow, the whole frame turns black. Maybe I need to mask out the scoreboard?

2) In that opening shot and in other shots, the scoreboard is partly visible, or becomes visible, etc. So how do I handle that? The tracker points move in and out of the frame, so I can't just let After Effects analyze the motion, right? How should I approach manually setting the keyframes?

Thanks in advance. If I had more time, I'd just dig into the manual and try a lot of things out, but I'm under a bit of time pressure, so pointing me in the right direction would be great.

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Michael SzalapskiRe: Need to key out green screen AND yellow markers as the screen moves into the frame
by on Feb 3, 2011 at 5:49:12 pm

How are you trying to key out the yellow? Just put a color keyer effect on it before the Keylight pass and you could be good. (Obviously, it depends on the shot.

As for tracking it when it comes in and goes out of the frame, you could track it each time. Nothing says a track has to be one continuous thing.

- The Great Szalam
(The 'Great' stands for 'Not So Great, in fact, Extremely Humble')

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Angie TaylorRe: Need to key out green screen AND yellow markers as the screen moves into the frame
by on Feb 5, 2011 at 9:01:42 am

Hi there,

If you use Keylight to key out the Green, you can use the Outside Mask settings to create a Garbage mask for the Yellow marker. If there's more than one you could perhaps just mask them and animate the masks, this may be easier than trying to key them. If you are animating masks, always start by creating start and end keyframes, then going half way between keyframes till you have it following the path. Michael linked to a great resource to help you with this rotoscoping technique in his last post, here it is again,

I also discovered a handy little trick for when the tracker goes off screen. One thing to make sure you have selected in the Motion Tracker options is the 'Extrapolate Motion' setting. With this setting selected, when the tracker's 'confidence' goes below the set threshold, After Effects will look at the speed and direction it was moving in before it 'lost it' and will keep moving in that direction till the end. This sometimes works but may not if the tracker actually moves off screen as the Motion Tracker will not go outside the bounds of the comp. so, if you try that and it STILL doesn't work, here's another solution.

Track as much as you can and then apply the Tracking data. In the Timeline, scrub through to the point where the track goes wrong and delete all keyframes after that point. Then add an expression to the Position Value of the layer you are attaching (in the case of 4 point tracker this would be to each of the Corner Pin properties that are animated (Upper Left, Upper Right, Lover Left, Lower Right). Add the following expression to each property;


This will have a similar effect to Extrapolating but will also work outside the frame. Basically, all it does is continue the animation of the selected property at the speed and direction that was being followed when the kayframes stopped. A mightily handy expression!

Hope this helps, ping me with any questions.



Angie Taylor animation & illustration for television, film, web and devices
Twitter: theangietaylor
Linkedin: theangietaylor

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