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Tracking multiple monitors with moving shots (Mocha + AE)

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Doug Alvarez
Tracking multiple monitors with moving shots (Mocha + AE)
on Oct 27, 2013 at 1:43:49 am

Hey guys...
So I'm doing VFX for a buddies short film and I need to do screen replacement for multiple shots.
The catch is that there are up to 8 monitors in some shots. Here is an example of two: https://vimeo.com/77877568
So my tracks are looking really shitty: Imgur
Anyone have any tips or any good tutorials they could pass along? I have 50 shots to track, most with 3+ monitors in them and the camera is constantly moving, sometimes with objects obstructing the monitor the entire shot.
Thanks for your help.


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Mike Jackson
Re: Tracking multiple monitors with moving shots (Mocha + AE)
on Oct 27, 2013 at 2:32:21 am

I've done a lot of shots like this... and you certainly have your work cut out for you.

Some people here may have other opinions, but I don't think this is a good job for Mocha. If I were doing these shots I'd use the 3D Camera tracker (added in CS 6 I believe?). Or better yet, if you can get ahold of a copy I'd use Boujou. Either way it's a problem best solved with a full 3D solution, so you're effectively mapping out all your monitor locations in 3D space, and thus having them move in and out of visibilty is much less of an issue.

That said, you're still looking at a lot of finessing. It looks like the camera this was shot on has a rolling shutter - Not as bad as on a 7D, but the jello-cam effect will definitely affect how well each screen stays where it's supposed to be. Not a lethal problem, but you'll probably have adjust the positions of all the screens subtly during pans and zooms.

Do you have camera focal length data from the production?



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Doug Alvarez
Re: Tracking multiple monitors with moving shots (Mocha + AE)
on Oct 27, 2013 at 2:37:22 am

Thanks Mike.

Does Boujou offer a trial? I've never used it.

And I'm awaiting that data from the director.

Just curious, about how long would you estimate it would take to do one shot like this?


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Mike Jackson
Re: Tracking multiple monitors with moving shots (Mocha + AE)
on Oct 27, 2013 at 8:07:47 am

Well, the first shot with a particular effect is always the trickiest... and (at least for me) often unpredicatable. But once you've gotten a good track, set up your compositions for keys, mattes, video screens, etc.,you should be able to bang most of them out using the same pipeline. Depending on how good the motion track was, and how complex the videoscreen graphics were, I could see it taking as little as a few hours or as much as a couple of days to get that first one working perfectly... assuming the rolling shutter doesn't throw you a curve ball.

But once all the screens were positioned in 3D space, it would be a lot easier to use that information (even just as a mental guide) to crank out the rest.

As far as Boujou goes, I'm not sure of its current availablity, or if there are demos. I got my copy many years ago, and it still outperforms anything else I've tried for this kind of shot, 70% of the time. Plus it lets you input your lens values in mm, rather than AE's awkward 'angle of view'.



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Roland R. Kahlenberg
Re: Tracking multiple monitors with moving shots (Mocha + AE)
on Oct 27, 2013 at 10:01:49 pm

mocha will certainly do an excellent job for screen inserts such as these. However, the issue is that each screen is on a separate plane. This requires you to track each screen separately. With a 3D track, you will only need to solve the scene ONCE.

If you're using AE's 3D Camera Tracker, ensure that you first mask out the foreground occlusion in a precomp prior to tracking as it will very likely interfere, negatively, with the tracking algorithm's requirements for a good track.

HTH
RoRK

Intensive mocha & AE Training in Singapore and Other Dangerous Locations

Imagineer Systems (mocha) Certified Instructor
& Adobe After Effects CS6 ACE/ACI


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Doug Alvarez
Re: Tracking multiple monitors with moving shots (Mocha + AE)
on Oct 27, 2013 at 10:19:45 pm

If you're using AE's 3D Camera Tracker, ensure that you first mask out the foreground occlusion in a precomp prior to tracking as it will very likely interfere, negatively, with the tracking algorithm's requirements for a good track.

^^^
So you're saying mask out everything in the shot but the monitors in a precomp?


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Roland R. Kahlenberg
Re: Tracking multiple monitors with moving shots (Mocha + AE)
on Oct 27, 2013 at 11:48:03 pm

[Doug Alvarez] "So you're saying mask out everything in the shot but the monitors in a precomp?"

Not everything! Just the characters/objects that are moving in the scene. Objects in the distance are not an issue. It's those that cut across the frame, close to the camera that are a huge issue.

HTH
RoRK

Intensive mocha & AE Training in Singapore and Other Dangerous Locations

Imagineer Systems (mocha) Certified Instructor
& Adobe After Effects CS6 ACE/ACI


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Darby Edelen
Re: Tracking multiple monitors with moving shots (Mocha + AE)
on Oct 28, 2013 at 5:01:18 am

[Roland R. Kahlenberg] "Not everything! Just the characters/objects that are moving in the scene. Objects in the distance are not an issue. It's those that cut across the frame, close to the camera that are a huge issue."

To expand on what Roland is saying, a camera solve depends on everything that's being tracked remaining stationary during the track. You're attempting to solve for the motion of the camera so all the of the reference points need to be static in the scene otherwise they will contribute incorrect motion to the tracks.

Foreground objects obscuring background objects are fine so long as those objects don't move.

Darby Edelen


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Roland R. Kahlenberg
Re: Tracking multiple monitors with moving shots (Mocha + AE)
on Oct 28, 2013 at 8:25:57 am

Well said Darby. You took the springs right out of my keyboard. :-)

Cheers
RoRK

Intensive mocha & AE Training in Singapore and Other Dangerous Locations

Imagineer Systems (mocha) Certified Instructor
& Adobe After Effects CS6 ACE/ACI


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