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superjab
02-18-2005, 12:48 AM
Hi everyone.
When people are filmed in real actions and we want to use a different location, a green/blue screen is located behind them, after filming the sequence you can substitute the background with some digital landscape or matte painting.

Do you know how to do this? i guess it is possible during the post production with after effects but i would like to have further information.
thanks

superjab

jussing
02-18-2005, 12:51 PM
Well, the simple answer is you use your compositing program's keying feature. In After Effects, you right-click your footage, select Effect -> Keying -> Color key (for instance). And voila, you're flying.

The not-so-simple answer is that keying is a very complex craft, and you can never "just" do it.
Part of the art is to make a good chroma key background on set, get a good color, good material, light it well, make sure there's no folding/shadows.
Another part is getting the background to match, whether it's CG, live action, miniature.
And then, you have to pull a really good matte in compositing, and make sure you get hair, motion blur, transparency etc. to look good too. And that is not just a rightclick -> pull matte.

So, good luck. :)

- Jonas

superjab
02-18-2005, 10:46 PM
Thank jussing i appreciated the help.
Anyway i'm not quite sure if i understood it. Do you know any tutorials about matches real footage and digital landscape? Something step by step in After effects.
What i want to do is easy, i would like to know how i can achieve the effect. For instance, i film someone on a blu/green screen after that i do a CG animation and then i blend the video with the animation together in after effects.(put on the screen the CG animation and keep the real actor in foreground). That's all. Can you help me with thar? and telling me how to do it?

Thanks

CGmonkey
02-21-2005, 12:50 AM
Here's something to get you going..

http://www.creativecow.net/show.php?page=/articles/chromakeying.html

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