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Creating a ghost - no green screen.

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James MourCreating a ghost - no green screen.
by on Apr 23, 2008 at 9:19:05 pm

This is my set-up:

I have a clip of a girl walking to a corner, then kneeling down.

Then I have a clip of a guy in the same corner, sitting, waving his hands.

They both share the same exact background, the camera was locked. I need to make the girl (top layer) slightly invisible so that when played back - you can see the guy in the corner (real) and the girl walking through him (ghost)

Please help me, I've tried a dozen or so things.

Thank you so much.


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Dave LaRondeRe: Creating a ghost - no green screen.
by on Apr 23, 2008 at 11:04:45 pm

Dave's Stock Answer #2:

When you're out on a shoot, and you say, "we'll fix this in post" without knowing PRECISELY HOW you're going to fix it in post, don't shoot it! You'll only end up shooting it over again.



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...and you will end up shooting it over again. Since we're talking about a ghost, you can get away with shooting the girl against a perfectly black background. Yeah, it won't look perfect as a chroma key might, but hey -- it's a ghost, right?

To get the girl into the existing shot, use one of the Transfer modes: Add, Overlay, Screen, etc. and futz with the opacity. You might also use the Levels effect to completely eliminate the black background. Once it's gone, you toss in a bit of Tint, perhaps.

To get the girl to walk through the guy, you'll have to make a few animated masks to hide the girl as the enters the guy, and then to reveal her as she exits the guy.

So how do you set up the camera to make sure everything lines up? Well, that's your problem. That's why you have to know HOW you're going to do it BEFORE you shoot. Then you know WHAT to do.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Richard HarringtonRe: Creating a ghost - no green screen.
by on Apr 24, 2008 at 12:25:15 am

Spoken like a hawkeye =)


If the shots are both locked down... stack them on top. Change blending modes of top shot... then lower opacity



Richard M. Harrington, PMP

Author: Photoshop for Video, Understanding Adobe Photoshop, and ATS:iWork


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Dave LaRondeRe: Creating a ghost - no green screen.
by on Apr 24, 2008 at 3:54:50 pm

Hey, somebody who knows about Hawkeyes! Whaddya know?

----------------------------------------------------

If you use Richard's strategy, thus avoiding a re-shoot, know that you'll be animating a LOT of masks to get the image to look right: you don't want parts of the wall in the girl's shot affecting vast portions of the guy's shot.

This technique of animating masks is part of a process known as rotoscoping, and it is a very work-intensive and time-consuming process indeed!

Here's a link to a recent thread on the topic. Wade through it to get to the rotoscoping tips:

http://forums.creativecow.net/thread/2/932718

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Richard HarringtonRe: Creating a ghost - no green screen.
by on Apr 24, 2008 at 4:53:07 pm

Thought he said cameras were locked don with same exact background...

I fully agree with your think before your shoot advice....




Richard M. Harrington, PMP

Author: Photoshop for Video, Understanding Adobe Photoshop, and ATS:iWork


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Dave LaRondeRe: Creating a ghost - no green screen.
by on Apr 24, 2008 at 5:17:54 pm

[Richard Harrington] "Thought he said cameras were locked down with same exact background..."

Right. Which means that any transfer mode applied to the "girl" layer will be seen on the "guy" layer... in fact, right over the guy. I'm assuming the poster wants the guy and his background to look normal, which means isolating the girl. That's why I'm thinkin' masks.

Then there's the trick of making the girl walk through the guy: masks again.

And the poster never does say what the background is like. If it's black, life is good for him and I'm wrong... but it could be a brick wall, for all we know. So I gave worst-case advice.

Glad we're agreed on the "think before you shoot" thing.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Dave LaRondeRe: Creating a ghost - no green screen.
by on Apr 24, 2008 at 7:00:56 pm

Now, if the guy can create a clean plate out of the two pieces of video..... or, dare I say it, actually shot a clean plate, another option opens -- a Difference Key or a Difference Matte, whichever it's called in AE.

The downside to using it is that it's really hit-and-miss in its results.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Thomas LeongRe: Creating a ghost - no green screen.
by on Apr 24, 2008 at 7:33:59 pm

A re-shoot with a set for the Pepper's Ghost effect could probably achieve what you want without any post-pro required. An explanation of the principles behind Pepper's Ghost can be found at http://www.phantasmechanics.com/pepper.html
and at http://www.doombuggies.com/home.php for Disney's Haunted Mansion effect.

The guy is in the room with the furniture, etc. The girl in the other. Needs some really critical lighting of the background in the room where the guy is, in order to get the girl looking opaque in areas where you want her to be solid. Getting her looking transparent is simple - she will look transparent wherever the background (of the guy's room) is brightly lit.

To get the girl to walk through the guy, use the principle of angle of reflection = angle of inflection (the distance of girl to mirror in one room = the distance of guy to mirror in the other room), and you will get the illusion of the girl walking through the guy.

Thomas Leong




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Dave LaRondeRe: Creating a ghost - no green screen.
by on Apr 24, 2008 at 8:12:17 pm

Ah, a practical effect! I like those.....

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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