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Using a clean frame instead of greenscreen

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Ori Lahav
Using a clean frame instead of greenscreen
on Jul 24, 2008 at 6:22:38 am

Hello,
How can I use a clean frame as a mask? For example, I have a footage of a car driving on a road, and I want just the car. I have one frame where you don't see the car. So, my idea is, simply mask every pixel in the footage that is the same as that frame, and what will happen is that the car will be the only part that won't mask out.

I tried to use "Difference" blending mode, but with not success.
Is it possible?

Thanks,
vbCrLf.


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Benjamin Tattersley
Re: Using a clean frame instead of greenscreen
on Jul 24, 2008 at 10:43:24 am

hey good question! ive been experimenting with this today and there are a few good plugins you could use. First i would suggest motion stabilizing your footage if you haven't already and line up your clean plate frame. Use the difference matte effect in the keying section of the effects panel. IF you want to generate a clean plate throughout your footage, i might suggest getting the boris continuum 5 plugins pack and it comes with a great motion key plugin to extract moving objects from your footage. Use this o generate a clean plate along with the remove noise and grain effect applied before it. copy and paste the remove noise and grain effect to another copy of the footage without the motion key plugin and you should have two perfect candidates for the difference matte plugin. Make sure you precomp the motion keyed footage before applying the difference key to the other footage because the difference key cannot 'see' effects. then you can use this as a track matte for another piece of footage if you want to keep the grain. I would suggest rendering this out before using it in a project because it will take a very long time to render.



Let me know how this goes and if you made any changes because my method isn't perfect but it should work.





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Ori Lahav
Re: Using a clean frame instead of greenscreen
on Jul 24, 2008 at 11:12:58 am

Hello Benjamin and thanks for your response.
The camera isn't moving, so its much simpler. I tried to use "Difference Matte" under "Keying", but its creates some holes in the car because pixels that are the same. I couldn't get it fixed.
Regarding BorisFX, I looked at their website. Thats way too expansive...

vbCrLf.

P.S.
The video I'm testing the ways to do it is from Video CoPilot tutorial "Car Hit":
http://www.videocopilot.net/tutorials.html?id=108
The clean footage of the car in the street.

P.P.S.
Andrew, if you read it, thanks for your great tutorials. I learned so much from them!
And also, my question is a good idea for a tutorial ;) Pretty useful thing.



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Chris Heuer
Re: Using a clean frame instead of greenscreen
on Jul 24, 2008 at 3:01:17 pm

The difference keyer seems to be the simplest and most direct way. Just duplicate the truck and do a quick roto mask to bring back any holes in the car. That truck isn't in the shot for that many frames and the motion is constant, should be easy!

Chris Heuer
Freefall FX, LLC


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Ori Lahav
Re: Using a clean frame instead of greenscreen
on Jul 27, 2008 at 4:16:34 pm

This is what I get (default): http://img137.imageshack.us/img137/5521/comp10000125hg0.png
I tried many things, but couldn't get it right. I think I will leave it... :

Thanks for your help,
vbCrLf.



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