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Old February 26th, 2009, 12:03 PM   #1
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Green Screen question regarding lighting of sets..

Hi everyone,

So, for a school project, I built a little mock-up cockpit of a spaceship. I planned to green screen the dashboard/viewscreen at the front of the cockpit so I could insert starfields, etc.

However,I'm having an issue with lighting and keying up the greenscreen. For scenes where I want to go to "red alert" and throw on a red gel to the set, the green screen does not key up properly because the gel changes the color.

I have now evenly lit the green screen separate from the set (and placed the screen about 2 feet away from the actual cockpit), but now how do I light the set without the set light's gels spilling onto the green screen?

Thanks,
Kareem

Last edited by Kareem Dimashkie; February 26th, 2009 at 12:35 PM.
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Old February 26th, 2009, 12:45 PM   #2
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Hi Kareem

Not sure I quite follow, but if you just want a red gel colour look on your shot after keying, why not just apply a colour in After Effects.. I use this a lot to colour up skies...blue or orange being the colour I prefer but you can choose any tone you like.. playing with the opacity to get the look you want.

I've found applying these filters in post pretty much the same as using a grad or coloured filter during the shoot.

Just an idea.
cheers
Gareth
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Old February 26th, 2009, 01:16 PM   #3
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Hi Gareth,

Thanks for the fast reply. I think you seem to be following me correctly. I want to have a red color for the "red alert" scenes, but doing it on set with a gel will cause the green screen not to key.

However, if I work with the color effects in After Effects, will that effect be applied to my green screen footage as well? I need to keep the Green Screen footage without any color effects. Only the set needs to be red.

Also, is there a way of doing this in Avid Media Composer?
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Old February 26th, 2009, 07:02 PM   #4
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Just a general workflow thing - pull your key and do the compositing first. Once you've got it all together, then apply your color effects (whether it's the red alert thing or any sort of color correction).

Good luck.

~~Dave
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Old February 27th, 2009, 12:51 AM   #5
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Quote:
Originally Posted by Dave Dodds View Post
Just a general workflow thing - pull your key and do the compositing first. Once you've got it all together, then apply your color effects (whether it's the red alert thing or any sort of color correction).

Good luck.

~~Dave

Thank you Dave. So I just got After Effects. I'm using Keylight 1,2 to key out the green screen.

Now, for the "red alert" tint, what effect should I use in After Effects?

Thanks for the good luck! So far so good.

Kareem
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Old February 27th, 2009, 02:07 AM   #6
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Kareem...

Get the green screen as far away from the "set" as possible. That way your set will be isolated from any lighting used to illuminate the green screen.

Set the green screen's exposure so that it's at 50 IRE in the camera.

Then set up the lighting for your spaceship set.

You can place markers on your green screen to "lock" the star field in the spaceship's windows. Use the "tracker" in After Effects to provide the necessary motion data to lock "stick" the starry background to the fixed green screen. It's possible to shoot handheld while getting a realistic sense of movement in your foreground. Do some tests before committing to an actual project if possible.

After you pull your key with Keylight, you can adjust your color using the "curves" effects filter. It works just like the "curves" tool in Photoshop.

When you get it done, let us see it! :-)
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Old February 27th, 2009, 11:55 AM   #7
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Thank you for the help, Dean.

Is there a tutorial as to how to use the Motion Tracker in After Effects?

I'm a little confused as to how Motion Tracker is used. I understand that it will lock the star field onto the window, but I don't understand why I can't use Keylight for all of it. What is the benefit of motion tracker?
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Old February 27th, 2009, 12:41 PM   #8
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Kareem...

There's a lot of tutorials by Andrew Kramer on After Effects:

VIDEO COPILOT | After Effects Tutorials & Post Production Tools

There's certainly one that demos the built-in tracker.

Keylight's job is to create a matte, differentiating the green backdrop from everything else in the scene. The tracker is used to keep track of the position of a target in the scene. That motion data can then be used to either stabilize the entire scene or lock an element to a target.

If your camera moves during the spaceship scene, the stars have to be locked to a distant background. In the studio you would need to place markers on the green screen, and the green screen should be placed as far from the spaceship set as possible.

In post the markers would be tracked. The resulting tracking data would then be used to lock the star field onto the plane of the green screen.

As for Keylight's capabilities, it can do a pretty good job in general. But to maintain a maximum amount of detail and to control spill, I find Primatte much more flexible. Among the most powerful tools is Lightwrap. It has its share of problems and I don't use it all the time, but it's able to accomplish certain things that are very difficult to achieve otherwise.

Another helpful technique is rotoscoping. I have a separate tool for that called Silhouette. It's superior to AE's built-in masking tools if you have to do a lot of roto work. And its tracker is much better than AE's. It tracks targets that AE would give up on, and tracks them with greater accuracy. Not as convenient as AE's built-in tracker but if you have to do a lot of rotoscoping and depend a lot on tracking, the tools are well worth the price.
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