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How do I cut a chroma key shape and export it with alpha channel in motion?

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Andrei PopaHow do I cut a chroma key shape and export it with alpha channel in motion?
by on Jul 6, 2014 at 9:47:42 pm

Hi there,

I got a person in a blue full body suit, so I'm doing kind of a reverse chroma key, the person being the chroma, not the background.

So I'm keying this person.

Now what I want to do is to have only the shape of the person, on an alpha channel.

Question #1: How do I do this?

Question #2: Is there a different way to do this than chroma key or rotoscoping?

Thanks,


Andrei


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Robin S. KurzRe: How do I cut a chroma key shape and export it with alpha channel in motion?
by on Jul 7, 2014 at 11:00:40 am

[Andrei Popa] "Now what I want to do is to have only the shape of the person, on an alpha channel.

Meaning the person stenciled or the background? Set the key and invert as needed. Render out with ProRes 4x4 to retain the alpha.

[Andrei Popa] "Is there a different way to do this than chroma key or rotoscoping?"

Not that I can think of. Other than maybe a difference key. But that would dictate having a static shot and a clean background plate. But I doubt the results would be all that much better, if at all. Sometimes it even calls for a combination of all three.


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Andrei PopaRe: How do I cut a chroma key shape and export it with alpha channel in motion?
by on Jul 7, 2014 at 12:06:19 pm

Hi Robin,

Done the Alpha Channel.

I have this keyed out and alpha'd person, and I want to combine it with another layer that contains another person, and I'd like the layers to behave Photoshop style.

By that I mean either one should cover the other, depending which one is on top.

I can't manage to do that.

No matter which layer is on top and what blend mode I use, both layers as visible.

I would like one person to cover parts of the other, depending how they move in the picture.

Any thoughts on this?

Andrei


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Robin S. KurzRe: How do I cut a chroma key shape and export it with alpha channel in motion?
by on Jul 7, 2014 at 12:40:43 pm

[Andrei Popa] "No matter which layer is on top and what blend mode I use, both layers as visible."

Sorry. Maybe I'm just a little thick, but I'm not getting what you're trying to do or how that is possible, no. Maybe you could post a screenshot to clarify.


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Andrei PopaRe: How do I cut a chroma key shape and export it with alpha channel in motion?
by on Jul 7, 2014 at 2:21:16 pm

http://tinypic.com/r/vreq92/8

In the picture above I have the keyed out person (black) on top of the other person.

I get get this or blended, but never the girl on top of the keyed person.

I just think I realised while it's not working while writing this.

The keyed person is alpha, but the girl is with the background.

So I would actually need 3 layers, background, girl alpha, keyed person alpha.


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Robin S. KurzRe: How do I cut a chroma key shape and export it with alpha channel in motion?
by on Jul 7, 2014 at 2:24:28 pm

Erm... yes. If she is on the same layer as the background, how are you going to place something "between" her and it?


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Andrei PopaRe: How do I cut a chroma key shape and export it with alpha channel in motion?
by on Jul 7, 2014 at 3:03:02 pm

Yes, compositing is not my main thing, and I think I was kind of blocking that out of my mind, because the girl would have to be rotoscoped, which is something I'd like to avoid....

Is there something like an auto-rotoscope tool, or some kind of mask that auto-follows a shape, or another way to cut the girl out without rotoscoping?


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Robin S. KurzRe: How do I cut a chroma key shape and export it with alpha channel in motion?
by on Jul 7, 2014 at 3:08:30 pm

With THAT background? Sorry, but you'd have had to shoot it completely differently to spare yourself a roto. The only thing I can think of that might be of some help is SliceX. But only if the girl is practically motionless.

It helps to figure out what (and how) you want to do something before you start shooting. Otherwise suffer the consequences. ;)


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Andrei PopaRe: How do I cut a chroma key shape and export it with alpha channel in motion?
by on Jul 7, 2014 at 3:13:58 pm

"It helps to figure out what (and how) you want to do something before you start shooting."

That's exactly what I'm doing now, this is a test.

I wanted to see if there are any benefits of shooting the characters separately.

It works pretty well together (both characters shot at the same time).

Looks like shooting them separately in this case is an unnecessary pain.


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Robin S. KurzRe: How do I cut a chroma key shape and export it with alpha channel in motion?
by on Jul 7, 2014 at 3:24:36 pm

[Andrei Popa] "Looks like shooting them separately in this case is an unnecessary pain."

How could that be a bigger pain than having to rotoscope her? You'd merely need a small green screen behind her and a clean plate (assuming the camera is locked).


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Andrei PopaRe: How do I cut a chroma key shape and export it with alpha channel in motion?
by on Jul 7, 2014 at 3:38:56 pm

True, only that I was saying:

By shooting them separately I meant to rotosocope.

If I shoot them together and key the person in the suit it works fine.

Nevertheless, your option of greenscreening both is even better.


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Atiqur SumonRe: How do I cut a chroma key shape and export it with alpha channel in motion?
by on Jul 9, 2014 at 9:52:18 am

what you're trying to do


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