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Possible to track sky with single foreground object?

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Danny Mulen
Possible to track sky with single foreground object?
on Aug 23, 2012 at 3:57:21 am

I wanted to replace my sky but I made the mistake of shooting from a low angle so I didn't get any buildings in the shot...only my subject and the sky itself (very low contrast sky).

I'm asking if anyone knows any techniques to solve for the background or camera using just the foreground, and a background that has no real track points (just very blurry wisps of cloud that mocha can kind of track but its a glidecam shot so they keep going out of frame).


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Ross Shain
Re: Possible to track sky with single foreground object?
on Aug 23, 2012 at 4:34:39 pm

If there are enough clouds in the sky, you should be able to use mocha to track. One technique is to "unlink" the layer, so it does not move. As the camera pans and clouds go off-screen, the unlink planar track will create a track offset.

An alternate approach might be to track a static foreground element with mocha AE or Pro v3. Do a camera solve and then push the solved track in z space to approximate here the sky plane is.

Best of luck,
Ross

Ross Shain
Imagineer Systems
http://www.imagineersystems.com


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Danny Mulen
Re: Possible to track sky with single foreground object?
on Aug 23, 2012 at 7:24:48 pm

The problem is the guy in the foreground is throwing his arm around a lot and doing a whole bunch of body movements so I'm whipping the camera around to keep him in frame. So he's not exactly static, but I do like the idea of doing a camera solve and then pushing the track back further in z-space to get closer to the way the sky moves.

What did you mean by unlinking the layer so it does not move? Is there a tutorial for this? I would love to learn how to create a track offset but I'm not sure how.

Also how can I use one tracking spline, the instant it goes off frame or gets covered by the subject I add in a new spline elsewhere and continue? What im asking is how can I go about doing the offset tracking like you recommend?


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Ross Shain
Re: Possible to track sky with single foreground object?
on Aug 24, 2012 at 1:47:32 pm

You would need to track the ground or some other element in the foreground that is completely static.
If not possible, your best bet is to track the clouds. As the cloud goes offscreen, stop the track and move the shape search area back on screen to another cloud area (avoiding the actor). This will create and offset track.

Ross Shain
Imagineer Systems
http://www.imagineersystems.com


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