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How to track the shape of a moving human being?

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Andrei Popa
How to track the shape of a moving human being?
on Jun 9, 2014 at 6:31:34 am

Basically what I want to do.

A human is walking towards the camera.

I want to be able to track the shape of this human, which will be changing in size as it approaches the camera, and is moving hands, etc.

And at the end have kind of a shadow that is in place of that human.

How do I do this, what software do I need to do this.

I want to know how to do this by selecting the shape and tracking it, not via chroma key.

Thanks,

Andrei


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Robin S. Kurz
Re: How to track the shape of a moving human being?
on Jun 9, 2014 at 9:07:35 am

Unless the person is very easy to differentiate from the background and surroundings... as in REALLY easy... you'll be extremely hard pressed to find an *automated* way of doing this. You're more likely than not reduced to rotoscoping and keyframing frame by frame. Something you can in fact do extremely well with Motion and its b-spline masks.

Otherwise the only other option would be an app such as Mocha which can in fact track root splines. But again, for that to work well, your footage would have to fill several criteria. If it doesn't, then you're better off just rotoscoping it as described above right off the bat.


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Andrei Popa
Re: How to track the shape of a moving human being?
on Jun 9, 2014 at 1:14:35 pm

It should be really easy.

It a person in a full blue body suit (including head) against a white wall.

So the person is actually the chroma key, not the wall.

I'm quite happy with the results but I was looking for different ways to do it, to see what they offer and what I can come up with.

What would be the "automated" way you could do it if it is really easy to differentiate between the body and the surroundings?

And what is a root spline?

Thanks :)


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Mark Suszko
Re: How to track the shape of a moving human being?
on Jun 9, 2014 at 2:22:31 pm

What's the final effect you're going for? Something like the invisible alien in "Predator"?


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Andrei Popa
Re: How to track the shape of a moving human being?
on Jun 9, 2014 at 2:25:27 pm

More like a creepy shadow...

As I said I did chroma key and got both the creepy shadow and the Predator.

I was just wondering of other ways to do it, and if that could bring something different.


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Mark Suszko
Re: How to track the shape of a moving human being?
on Jun 9, 2014 at 3:31:52 pm

"What would be the "automated" way you could do it if it is really easy to differentiate between the body and the surroundings?"


You could try a difference key, I suppose. It looks for only the pixels that have changed from frame to frame. If the lighting on the body is strong and there is a sharp difference in the background lighting, you could artificially enhance that difference with the color correction tools until it create a hi-con traveling matte. Then you save off that traveling matte to a layer, restore the original footage, stack the matte in between layers and play with the effects. It would be a bit of work, and not sure it's any better for results than using an extract tool or rotor-brush.


One other idea that comes to mind, would be to use Poser to animate a mannikin as a flat 2-d black silhouette. You could theoretically extract tracking data from the live actor and apply it to the mannikin. Render out the mannikin's movements and being that into FCP or Motion for further compositing work. I think the complexity level of something like that points to AE as the better tool set for whatever the final product is supposed to be.


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Andrei Popa
Re: How to track the shape of a moving human being?
on Jun 10, 2014 at 7:53:33 am

Hey Mark,

Thanks for making me aware of the rotor-brush, it opens up quite a bit of possibilities.

:)


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