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How to isolate (mask) person walking in front of TV screen

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Leon Zandman
How to isolate (mask) person walking in front of TV screen
on Sep 14, 2016 at 6:41:07 pm

I have footage of a wall-mounted TV screen. Using Apple Motion 5's Match Move motion tracking tool I replaced the image that was displayed on the TV with some fake imagery. However, during part of the footage some person is walking in front of that TV. Because the match moved fake layer is on top of the original footage, the person disappears below the fake match moved content.

I'd like to isolate this person (i.e. create a mask that perfectly isolates him), so that I can duplicate the original footage and put that person in front of the fake video that's supposedly playing on the TV. How can I do this (in Apple Motion 5)?


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Robin S. Kurz
Re: How to isolate (mask) person walking in front of TV screen
on Sep 15, 2016 at 8:36:28 am

The answer is in the question, no?

[Leon Zandman] "create a mask that perfectly isolates him, so that [you] can duplicate the original footage and put that person in front of the fake video that's supposedly playing on the TV"

… then keyframe. I.e. rotoscope.

- RK

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Leon Zandman
Re: How to isolate (mask) person walking in front of TV screen
on Sep 15, 2016 at 10:49:50 am

While I do have a general idea on how to proceed, I'm still confused on how to isolate the person. You say keyframing / rotoscoping. This means adjusting the mask for each frame by moving the control points, right? That's a lot of work (hundreds of frames) and I doubt I can get the mask to fit tightly around the person. This probably won't look good, even if I feather the edges of the mask.

Now that I think about it some more, I guess what I need is to use a garbage mask to remove everything outside the TV's screen and treat the TV screen as a green screen / chroma key and use a keyer to isolate the person from the background (which is the TV screen). However, the TV screen is displaying a running video and doesn't have a solid color.

Any ideas?


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Robin S. Kurz
Re: How to isolate (mask) person walking in front of TV screen
on Sep 15, 2016 at 12:41:04 pm

From what you describe, I have no idea how you are going to get around rotoscoping. Which, yes, is a huge PITA, depending on the footage. Things one has to think of ahead of time.

- RK

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Leon Zandman
Re: How to isolate (mask) person walking in front of TV screen
on Sep 15, 2016 at 1:17:44 pm

Yes, but this was existing footage. Didn't plan to add SFX to it. I'll fiddle with it some more.

Maybe some other forum users have an idea?


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Bret Williams
Re: How to isolate (mask) person walking in front of TV screen
on Sep 15, 2016 at 3:16:37 pm

Can you edit out the person walking in front of the TV? Probably not if there's other things going on that are needed. So then it's back to masking/Royo. You can either root the TV, or root the person. Putting green on the TV isn't an option. You'd have to roto to get green in the tv. Might as well roto the person and put what you want in the TV.

Why would it be hundreds of frames? How slow is this person? And why would it require adjusting every frame? Are they dancing? Doing sign language? A person walking by is often a pretty uniform shape. A start mask, end mask and a few Keyframes in between is sometimes all you need.

SliceX might help automate.

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Leon Zandman
Re: How to isolate (mask) person walking in front of TV screen
on Sep 15, 2016 at 7:43:27 pm

I figure I would need to adjust quite a lot of frames, because I think the mask needs to be near pixel-perfect to be convincing. That's why I think the manual route is too tedious.

Normally you'd use chroma keying. Now the TV screen isn't a perfect chroma key background. But it does differ substantially from the person's image. So I figure I should be able to create a mask using other ways. I know in Photoshop I can isolate things from their background by creating a mask based on one of the split RGB channels. Or by looking at the luma values. This should also be possible in Motion. I've just never done it.


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Matt Galuszewski
Re: How to isolate (mask) person walking in front of TV screen
on Sep 16, 2016 at 9:31:44 pm

Are you able to export and upload the section of the video where the person walks in front of the TV screen?



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