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Tracking a glass "iPad"

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Stuart Samuels
Tracking a glass "iPad"
on Feb 27, 2014 at 1:19:16 pm
Last Edited By Stuart Samuels on Feb 27, 2014 at 1:19:34 pm

Hi.

I have been asked to help with some VFX for a sci-fi short. The art dept have created a glass "iPad" (below) that I have been asked to create and composite a semi transparent medical readout screen on to.

Does anyone have any advice on how to go about getting a solid track? I've done numerous tests in Mocha but the track drifts way to much (even after using the Adjust Track feature) as there's not much for it to grab on to and the reflections screw it up. I have suggested shooting some more test footage with tracking markers in each corner but then I'm concerned about removing the markers....

Here's a still from the test footage. (NB. There is some movement in the actual footage that causes reflections to move etc):




Thanks for any help anyone can offer.

Stuart


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Gardner Raymond
Re: Tracking a glass "iPad"
on Feb 27, 2014 at 2:20:44 pm

No initial help for the tracking question (sorry), but If you're going to have them re-shoot anyway, have them do a few with the talent holding nothing instead if the piece of glass. It might be easier to re-create the entire thing in AE and use the tracking data of her hand rather than trying to track and composite on the glass.

Actually, a thought for the tracking - can you just use the very edges of the glass where there's less reflections? It looks like they're pretty solid...


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Roland R. Kahlenberg
Re: Tracking a glass "iPad"
on Feb 27, 2014 at 3:21:46 pm

Extraneous movement in the background, behind the glass as well as the reflections will throw off mocha's tracking engine. As Gardner has advised, try tracking just the edge of the glass. Add additional tracking points on the fingers to see if this helps with the tracking results.

If the above do not help, then keep the background textures simple. Use either a chroma card that the talent holds, as a mock up for the glass OR use the glass but with a chroma card in the middle to act as a tracking marker - these steps will make tracking a lot easier.

HTH
RoRK
Latest AE Workshop - MoGraph Intensity - Shapes & Text

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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Bobby Yarsulik
Re: Tracking a glass "iPad"
on Feb 27, 2014 at 8:33:02 pm

Could even doing a layer over the entire piece of glass just outside the border, and then an inner layer that doesn't track within the inside of the glass just inside the edge do any better with the footage you already have?

I had an issue with a television screen earlier this week, and this helped tremendously.


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Stuart Samuels
Re: Tracking a glass "iPad"
on Feb 28, 2014 at 9:25:59 am
Last Edited By Stuart Samuels on Feb 28, 2014 at 10:17:24 am

Thanks everyone, really great suggestions. Very much appreciated.

Even tracking the hands or edges seems to throw the tracker off. I can't work out why, I've had great results in the past using a similar method.

Could ask for any tips on removing the chroma card in post before I comp the display?

Thanks again

Stuart


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Stuart Samuels
Re: Tracking a glass "iPad"
on Feb 28, 2014 at 11:12:37 am

Would you be able to expand on the chroma card idea please? The more I think about it the more I don't understand how it could work!

If the talent holds a green card rather than the tablet how would I accurately replace what we would see through the tablet (eg, fingers, knees, floor etc)??


Thanks


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Roland R. Kahlenberg
Re: Tracking a glass "iPad"
on Feb 28, 2014 at 11:16:24 am

[Stuart Samuels] "Would you be able to expand on the chroma card idea please? The more I think about it the more I don't understand how it could work!

If the talent holds a green card rather than the tablet how would I accurately replace what we would see through the tablet (eg, fingers, knees, floor etc)??"


I did qualify that the background needed to be simplified. You have however now mentioned an issue that I didn't foresee - the fingers. So holding only a chroma card isn't going to work. You can however place it in the middle of the glass - as a tracking marker.

BTW, have you tried tracking just the edge of the glass + the fingers?

HTH
RoRK
Latest AE Workshop - MoGraph Intensity - Shapes & Text

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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Stuart Samuels
Re: Tracking a glass "iPad"
on Feb 28, 2014 at 11:47:42 am

Thanks Roland. You did mention keeping the background simple and now I see why.

I did try tracking the edge and fingers but I could barely get through a couple of frames without the track drifting. I feel there may be another issue that I'm not seeing as I don't understand why it did such a poor job.

Thanks for the advice, I'll keep chipping away....


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Bruce Holt
Re: Tracking a glass "iPad"
on Mar 1, 2014 at 3:56:10 pm

You might be having a difficult time tracking the edges because the lighting will change the Luminance of the edges as the glass moves. You might try "Auto Channel" and see if that works any better.

It'll be a pain in the "glass" (sorry couldn't resist), but I just did a number of similar shots. If they haven't shot it already, put ~1/4" trackers on the glass at the corners of an imaginary 4-6" square in the center. In mocha, use four splines on the same layer to select the trackers and you should be good to go. You'll have to paint the trackers out, but at least you have the roto-splines already in place. You'll probably also have to re-create some reflections, but I found that using the offset method of removing the trackers got most of the background work done. I've uploaded your image with an example in case my description doesn't make sense.


It's probably not the most elegant way and at first I was cursing the crew for placing the gaffers tape on the glass (I wasn't on set), but in the end it saved my bacon.



bruce

bruceholt.com
VFX Artist


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Stuart Samuels
Re: Tracking a glass "iPad"
on Mar 1, 2014 at 5:22:10 pm

That's really great, thanks Bruce. I'm going to send your image over to the director.

I'll probably be back at some point to ask for tips on painting out the markers!

Thanks for all the advice, it's really appreciated.

Stuart


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