i have a character that holds a sign that has been painted green, how can i motion track him and use green screen footage to put on the sign, i have AE 7.0 and PP

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Mac G5 workstation with 4 gigs of ram, 4x250 gig drives in raid 5. High availability cluster server running centos for a server. 2xCanon GL2 cameras.

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not sure if these words translate into AE at all but the simplest way I can think of to do this is take your image or clip and corner pin it to the edges of the sign and then keyframe these corners over time.

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I'm not young enough to know everything!

You can use Alan's way with the effect Effect>Distort>Corner Pin, and keyframe each corner over time, or you could use the perspective motion tracker, which tracks the footage and basically keyframes the corners for you. However, depending on the footage it may be easier just to do it manually with Corner Pin. Here's a tutorial on the motion tracker.http://studio.adobe.com/us/tips/tip....aft65cornerpin
Hope it helps. Peace