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Green Screen

K

kaz

:grumpy: Hi, I'm very frustrated with keying green screen footage in after effects. I'm using primatte and the key correct suite. However, even after following all the rules / steps, my actors have a distortion / snow / digital look when I ram preview it. Especially the edges and shadow areas. Any advice? It is filmed on xl2. :weird:
 
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Try using the Keylight plug-in. Should be in your key effect menu. I was having the same issues, then saw Andrew Kramer's tutorial on keying and he recommended Keylight. The difference was amazing!

If you haven't already discovered the site, it might be worth a visit to videocopilot.net.
 
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Just a guess, but it could be that you're RAM previewing it at quarter quality or something, which is why it doesn't look too good. Like Graeme said it'd be much easier to work it out if you post a screenshot though.
 
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Here is the snippet of video. It's awful. The edges are really transparent because of all the edge blur , etc. I had to do that much just to take the flicker down and you can even still see alot of distortion on the clothes and skin, and edges.

http://vimeo.com/11258226

ps. I'm not doing adult video or anything, this just happens to be a scene I'm working on right now in a short film. Just to put that out there =D
 
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Could you post the original as well so we can see the screen as well?

One of the tricks that work is to perform a chroma blur before keying... if you can convert the image to YUV, then blur the U and V chroma... the luminance holds the edge detail and doesn't get blurred. That will help clean up the edges a bit.

DV is notoriously bad at greenscreen due to the low chrominance information (XL2 is 4:1:1).

A couple of the tricks are to make sure you're using as many pixels to capture your subject as possible. Back light the subject with a slightly yellow/orange light to separate them from the background. Make sure the screen is light slightly brighter than your subject.

I'd be interested to try Oakstreet's Vector Keyer on this as well as it looks like the type of thing that would do well with it.
 
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I managed this in five minutes or so… one curves layer, one instance of Keylight and a simple rectangular matte. To be honest I'm not sure you're going to be able to key it very well - it's not that high resolution, quite noisy and some of the edges (especially hair) aren't well defined enough. Your best bet might be chroma key and a little roto for the more complex portions.
 
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I've played and I can't get much better than the original... I'm going to try a trick I saw with some hardcore math stuff somewhere to see if I can make a better key for it. It's quite grainy, which leads me to believe your gain got raised either through it being set to auto, or turned up by the Cam Op.

I started by performing some color correction to get rid of a little bit of the grain in the darks... then pulling a key with keylight, then blurring the alpha channel slightly, then reapplying that matte to the original image.
 
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OK, I got really pristine edges off of the bright sides of the subject, but there was simply not enough separation between the screen and the darker portions of the subject.

the grain and the spill on the screen and the model made too much similarity between the foreground and background edges.

difficult.

Image attachment may be considered NSFW, but isn't too risque, just a model in her underthings... more coverage than some swim suits.

http://www.yafiunderground.com/Images/key_test.png
 
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That could be cut apart to generate part of the edge matte... a core matte could rough out the main portion, then something to get a dark side matte...

couple these with a garbage matte to limit the amount of math that has to be done and you could pull an OK matte out of this, it'd still be easier to reshoot with a stronger lit background and the gain on the camera corrected. You'll save time in the long run.
 
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