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Object replacement using 3D Camera Tracker advice.

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Stephen PickeringObject replacement using 3D Camera Tracker advice.
by on Aug 20, 2013 at 5:53:34 pm

Hi there,

I know there are many posts about this but I'm not figuring it out with my project. I know how to add logos, etc. to a 3D tracked camera scene, but I have some objects needing removal. Specifically it's a panning shot of an operating bed with a folded blanket sitting on it. I need to remove the blanket which covers part of top of the bed plus a bit of the wall which is behind the folded blanket. So I guess it would be the wall plane as well as the table plane.

If I were to replace the top of the bed with a clean plate does that mean I need to create a flat, 2d top of the bed (ie, remove the perspective distortion) or can I simply photoshop the first frame and have AE warp it to match the 3d Camera Tracking from the first frame on? Same for the wall. Do I have to have to create a perspective-free plate?

I know I've seen tutorials about this. Are there some you can recommend?

Thanks!
-Stephen



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Stephen PickeringRe: Object replacement using 3D Camera Tracker advice.
by on Aug 20, 2013 at 6:31:42 pm

Here's the example shot to show what I'm talking about. Again the camera is panning and it's a wide lens so there quite a bit of distortion during the pan.

Thanks!



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michael zoppoRe: Object replacement using 3D Camera Tracker advice.
by on Aug 20, 2013 at 7:11:45 pm

You will need to create a perspective free texture/image of the bed without the blanket on it. Then you'll need to make it a 3d layer and line it up with the top of the bed till it looks correct, then play through the video and see how well it matches up with the pan. If you tracking data is good then you should be good to go.

A few issues may arise though. One of the biggest is that you when you line it up on the first frame or whatever frame you choose and then start playing it back you may start to see the top of the bed (the texture you created) start to slide or not "stick" to the top of the bed. This is usually not because your tracking data is bad, you may have just pushed it too far back in z-space or too forward. A parallax effect basically. It's going to take some trial and error to nail it down. If you're still having a lot of issues you may want to think about actually selecting a few of your track points that are on the bed and then use them to create a null and parent the bed texture to the null to make sure it sticks and even then you may still encounter sliding issues.

The back wall may be a little easier to get done. If you're trying to remove that whiteboard it should be fairly easy, just recreate the wall texture, feather the edges, line it up in the shot and 3D space and then play it back to see how it looks. You may have to do a tiny bit of rotoscoping on that medical device that is in front of the whiteboard though.

I'm not an expert compositor or tracker, these are just the issues I usually encounter when doing this sort of stuff.

Good luck!





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Stephen PickeringRe: Object replacement using 3D Camera Tracker advice.
by on Aug 20, 2013 at 7:19:09 pm

Thanks Michael,
That was my biggest question about the need for a perspective-free replacement layer. Your answer isn't what I was hoping for :) Would Mocha be the same? I only have the Mocha that comes with CS6 and I am not too familiar with it. There are a few shots with similar pans needing some object replacement so I'm happy to learn the best process as I'll be using it in this project a few times.

Thanks again,
Stephen



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Stephen PickeringRe: Object replacement using 3D Camera Tracker advice.
by on Aug 20, 2013 at 8:04:04 pm

So I've discovered the perspective crop tool in Photoshop and I love it. I tracked the scene and created a null and Camera from the top of the table. Now, why when I drop the perspective-free (3d layer) plate into the AE Comp and Shift drag the parent pickwhip to the Null I get a bazaar placement of the replacement layer. What am I doing wrong?

Thanks!
-Stephen



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Stephen PickeringRe: Object replacement using 3D Camera Tracker advice.
by on Aug 20, 2013 at 10:38:07 pm

Well, I didn't find the answer to why the placement went crazy, but I did figure out a way to use grids. I simply moved the grid layer around until it matched very closely to the real plane, then I duplicated additional layers grid layers and rotated -90 degrees to essentially build a 3d room. Then I was able to attach anything anywhere. I'll post the results.

Thanks again for your advice.
-Stephen



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Stephen PickeringRe: Object replacement using 3D Camera Tracker advice.
by on Aug 21, 2013 at 5:24:48 am

Here's what I ended up with.








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