View Full Version : Having troubles with keying out blue-screen footage

07 July 2011, 08:36 PM

i'm working on a short movie which involves a several blue-screen shots that needs to be keyed.

the problem is, that they start like this:

(there's this little device with a blue screen replacing it's original screen, and it's beeing lifted upwards by the actor):

and when it gets lifted, it ends up like this:

as you can see, it's the same shot, but due to the sun's direction, the lighting changes and as a result the color of the blue screen is not the same during it's movement.

when i'm keying it's first position (image #1). it turns out ok, but when i'm keying it's second position (image #2), its also keying out some other parts of the shot:

i'm using Keylight with After Effects CS5.

does anyone have any suggestions for me on how can i make this shot work?


07 July 2011, 12:49 PM
What about tracking the shape in Mocha and doing some roto in AE?

07 July 2011, 12:53 PM
possible, but it'll take a lot of time. there are 10-15 shots like this one, and alot of other motion graphics parts that needs to be done and we just won't make it until the deadline.. :/

07 July 2011, 01:34 PM
Well, the you should at least do some garbage-matting around the shape.

That should help the keyer to get better results.

Just to clarify:
Are you going to attach some graphical elements to this screen?
Because if you're planning to do so, you would have to track it anyways.

07 July 2011, 03:42 PM
ya i'm planning on attaching some graphic elements to the scene..

i can track it with mocha, the question is if it'll track this circular shape correctly as it moves in prepective, although it's color is changing a little.

07 July 2011, 05:31 PM
As long as the shape has enough contrast, the color-change should be no problem for the tracker.
Just make sure to activate the perspective tick-box in the tracking options and raise the minimum pixels used percentage number.
If the tracker fails, you can always make a duplicate of your shot, increase the contrast and use this version for tracking purposes only.

I've pulled off some very good tracks in Mocha from footage far worse than yours, so I don't think this will be a big problem.

Good luck.

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07 July 2011, 05:31 PM
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