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Old December 3rd, 2005, 12:43 AM   #1
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proper chromakey in Vegas?

Greetings everyone,

I have some footage involved green screen and would like to chromakey it in vegas. Unfortunately light wasn't setup properly and green screen wasn't evenly lighted.
here is a screenshot from the footage:
http://grand.homelinux.org/grand/green_screen.png

tried to use vegas chromakey, but didn't get any usable results.
Is there a way to do a good looking chromakey from this footage? if it's possible, how to do it?

Thanks,
Andrei.
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Old December 3rd, 2005, 03:52 AM   #2
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Quote:
Originally Posted by Andrei Grichine
Greetings everyone,

tried to use vegas chromakey, but didn't get any usable results.
Is there a way to do a good looking chromakey from this footage? if it's possible, how to do it?
Serious Magics Ultra will take care of it - we've had horrible chroma footage and Ultra had no problems at all, download the demo and give it a try at

http://www.seriousmagic.com/products/ultra/

/magnus
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Old December 3rd, 2005, 07:08 AM   #3
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Quote:
Originally Posted by Magnus Helander
Serious Magics Ultra will take care of it - we've had horrible chroma footage and Ultra had no problems at all, download the demo and give it a try at

http://www.seriousmagic.com/products/ultra/

/magnus
I've tried ultra version 1 some time ago and wasn't happy with it. It really softens and reduces resolution of video. I'll give a try version 2 maybe they've fixed that.
But I really would like to learn how to do a proper chromakey in Vegas. All my attempts are failed so far... even on example footage that comes with Ultra.
Thanks.
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Old December 3rd, 2005, 08:57 AM   #4
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I played around with it. It's not perfect but it might give you a start. I used a secondary color corrector to make the green more consistent and also to create the main key. I then added a chromakey effect set to the default green to help eliminate the remaining fringing around the people. Take a look at this and see if it helps give some ideas for getting a better key.

http://www.jetdv.com/vegas/cktest.veg
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Old December 3rd, 2005, 10:45 AM   #5
 
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Quote:
Originally Posted by Andrei Grichine
I've tried ultra version 1 some time ago and wasn't happy with it. It really softens and reduces resolution of video. I'll give a try version 2 maybe they've fixed that.
But I really would like to learn how to do a proper chromakey in Vegas. All my attempts are failed so far... even on example footage that comes with Ultra.
Thanks.

Andrei,
I dropped this into Ultra 2, and it does a reasonably good job. Just work in uncompressed modes.
Vegas can't pull this well, no matter what you do. Edward's veg is a reasonable start, even adding a chromablur to it will not give you a believable key.
However, if you use Vegas, you can do a few things that will help fix the issue:
1. Use a background that has a fair amount of green in it.
2. Use Pan/Crop to bring the subjects closer, thereby eliminating the airvent or whatever is above them, and the box that is to the lower left. You can attempt to use the Bezier masking tool to fix this, but that too, likely will not work believably well.
3. Create a garbage matte based on what Edward provided for you, but add a levels filter to it. Then use the garbage matte as a mask with a tiny amount of blur added to it. You'll have soft edges, but soft edges are preferable to aliased edges, IMO.
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Old December 5th, 2005, 11:02 AM   #6
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chromakey result

Thank you all for the support and suggestions. Here is a result I've got so far:
http://www.reaud.com/grand/salsa/
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Old December 5th, 2005, 11:09 AM   #7
 
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Quote:
Originally Posted by Andrei Grichine
Thank you all for the support and suggestions. Here is a result I've got so far:
http://www.reaud.com/grand/salsa/
Especially considering what you started with, that's quite good. You'd probably do a bit better creating a garbage matte and using levels filtering to clean it up, but it's very improved from what you posted as a still.
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Old December 5th, 2005, 03:05 PM   #8
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For what it's worth, the troubles you're having have more to do with the image quality than the software you're using.

What camera was this shot with?
What shooting mode? (16:9/4:3 / Interlaced or full frame)

The color channels are VERY blocky. Even more that would be expected from typical DV compression. Some of the color blocking extends beyond just 4 pixels wide.
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Old December 6th, 2005, 10:49 AM   #9
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Originally Posted by Nick Jushchyshyn
For what it's worth, the troubles you're having have more to do with the image quality than the software you're using.

What camera was this shot with?
What shooting mode? (16:9/4:3 / Interlaced or full frame)

The color channels are VERY blocky. Even more that would be expected from typical DV compression. Some of the color blocking extends beyond just 4 pixels wide.
It was shot with XL2 in 24p 16:9 mode. I understand that the problem is an image quality, unfortunately this is a footage i've got and it can't be reshooted.
I would appreciate any suggestions on proper shooting against a green screen for a future reference.

Thanks.
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Old December 7th, 2005, 09:07 AM   #10
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Wow, and XL2. These results are pretty surprising for that.
I was thinking that perhaps, if it was a non-native 16:9 camera, that shootin 4:3 would be better, but the XL2 is supposed to be native 16:9 right?

One thing that stands out is that the shot could be brighter.
The greenscreen green channel level is well under 200. Generally, it better to have your green values as high as possible without clipping, while keeping the blue & red values for the screen as low as possible.

Shooting using scopes like DVRack really help with adjusting your exposure values prior to shooting.

Is your camera always locked down for all the shots?
If so, you can use a clean greenscreen shot (no people) to help the keying process by allowing you to isolate the difference between a greenscreen only, vs people-in-front-of-the-screen shot.
I don't use Vegas, but DSE might have some specific instructions along these lines that would help.
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Old December 7th, 2005, 11:58 AM   #11
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Quote:
The greenscreen green channel level is well under 200. Generally, it better to have your green values as high as possible without clipping, while keeping the blue & red values for the screen as low as possible.
Some people suggest keeping the greenscreen lit dimly to keep spill down. Any thoughts on that?
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Old December 7th, 2005, 02:13 PM   #12
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Better to move your subject away from the screen to reduce spill than to dim the screen.

The trick is that many of todays digital keyers are based on a Color Difference calculation (not sure if this is true of Vegas), which thrives on the concept that, for the screen, a single RGB channel will have a very high value, and the other two channels will be very low. Many tools designed for DV will throw in additional refinement operations based on luma. Both of these operations (luma and color difference keying) work best when the green screen is as bright as possible without clipping.

Of course, this can lead to color spill, the greenscreen itself becomes a huge, green lightsource. :p
The better keying tools will have spill suppression as a built in feature, so spill becomes pretty much a non-issue.
This example shot has people LAYING on the greenscreen. Lots of spill on their skin, close to the screen, but the spill suppression adjustments in the keyer (Keylight in AE Pro) handle it pretty cleanly:
http://www.techvantics.com/demo/nej_demo_aoau_v02a.wmv

Have fun.
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