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Old March 11th, 2009, 08:15 PM   #1
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Green Screen Question

I plan on building a set that is roughly 10ft wide and we will be using green screen on it. The project will be shot in 1080i.

The question is. I have found some stock clips I would like to use on the green screen, but the ones I like are in 720x480. Will it still work? Or will I have to strech the image? Or will it work and just look like complete crap?

Thanks in advance...
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Old March 11th, 2009, 08:29 PM   #2
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Unless you can find the stock footage in the same rez as your 1080i footage, the only way the clarity of both would match is by downconverting your 1080i to match the 720x480 background footage.
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Old March 12th, 2009, 02:48 AM   #3
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If you're working with AE, upscale the background to 1080. Then do the composite.

Maintaining as much detail as possible with your foreground elements will help keep artifacts and errors to the smallest size possible and result in a much cleaner comp.
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Old March 13th, 2009, 11:10 AM   #4
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Do the math. 720x480 is not the same shape as 1920x1080. The SD footage will be both stretched and scaled if you uprez it to 1920x1080. It you uprez it and maintain the aspect ratio, you will be scaling it even more. How soft it gets after uprezing will be a function of how good it is at the beginning.

If this is your first green screen, this is the least of your worries. The first thing anybody will notice before the quality of your background is the quality of your keying. Lighting the background separately and evenly vs your foreground is critical. Practice definately makes perfect. Lots of articles written about it here. Google Walter Graff Tutorial for an excellent one.

To your question, you will get the best results from HD footage. If you are going to the web or SD DVD, then the prior suggestions of keying in 1080i for maximum foreground quality and uprezz your background composite then downrez to web/DVD are good ones.
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Old March 13th, 2009, 03:39 PM   #5
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Quote:
Originally Posted by Les Wilson View Post
Do the math. 720x480 is not the same shape as 1920x1080.
Of course it's not. You have to overscale 4:3 footage to fill a 16:9 frame.
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Old March 13th, 2009, 05:27 PM   #6
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Dean ... I could have been clearer ... I was responding to Michael's questions "Or will I have to strech the image? Or will it work and just look like complete crap?"
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Old March 14th, 2009, 03:19 AM   #7
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Dean ... I could have been clearer ... I was responding to Michael's questions "Or will I have to strech the image? Or will it work and just look like complete crap?"
Ok. Sorry about the confusion.
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Old March 14th, 2009, 12:26 PM   #8
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I've been using a lot of old Serious Magic SD backgrounds and scaling them up. They actually scale nicely, then I toss a little Gaussian blur on the background to soften it up. Here's an example Manfrotto Monopod demo shot in front of Reflecmedia backdrop on Vimeo
Depending on your footage it might be best to scale it up to fit in the HD frame, do your composite, then scale it all back down. It depends on what your final delivery method is as as to if it'll be noticeable.
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