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When Motion Tracking and Masks dont work...

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olaf steel
When Motion Tracking and Masks dont work...
on Jun 7, 2010 at 1:13:31 pm


I have been struggling for a while to do an effect in After Effects that sort of combines two pieces of video.
I have one clip of a projector and a small screen can be seen on which the projectors image is projected.
The second piece of video is of a boy walking.
I want to have the footage of the boy walking in the projection window so it looks like that footage is what's being played on the projector.

The links to those clips on youtube are below so you can get a better idea of what I mean.

The problems I've had is that there is a lot of movement in the shot with the projector, so its very difficult to create a mask for the video of the boy walking.
I have tried to motion track and stabilize, however, there are no continuous high contrast points to map to, as you can see in the videos. also the screen is not comprised only of 4 points, as the projector's lens covers part of it.

If anyone has any suggestions as to how I can make this work, please let me know. I will be very grateful indeed.

Thanks a lot,


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Tudor "Ted" Jelescu
Re: When Motion Tracking and Masks dont work...
on Jun 7, 2010 at 1:33:37 pm

The first thing I would say is to re-shoot with a green screen instead of the projected image... but, that may not be possible, so:
If you're using CS5 the new roto brush may be used to mask the projector.
If not- I would try to match first the screen- Mocha should do for this. Then roto out the classic way the projector and comp.

Tudor "Ted" Jelescu
Senior VFX Artist
Bucharest, Romania

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Roland R. Kahlenberg
Re: When Motion Tracking and Masks dont work...
on Jun 7, 2010 at 4:27:01 pm

Your main issue is that the projector's screen has imagery that is moving. This will mess up any tracker. But before shooting, see if you can track the edges of the projector's screen. If you can, then it's quite easy to create a shape in Mocha for export into AE to be used as a track matte for the fill (boy video).

Mocha will be able to do this easily if you had a static image in the projector screen. Mocha prefers static textures instead of solid colors.

The movements shouldn't be an issue as that's what the tracker is supposed to do.

Roland Kahlenberg

Sell your AEPs with broadcastGEMs' DVD series of templates. Click here for more

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