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Two step keying and track matte to get rid of noise from Keylight.

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Mitch HardisonTwo step keying and track matte to get rid of noise from Keylight.
by on Aug 9, 2011 at 12:45:33 am

I'm getting noise in my subject when I use keylight. I read a few threads with solutions but I don't understand. What is a two step key and how do I do it. Also how do I use a track matte to help. I tried but then it put a green line around the subject. I don't know what I'm doing.


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Todd KoprivaRe: Two step keying and track matte to get rid of noise from Keylight.
by on Aug 9, 2011 at 6:34:17 am

Read Mark Christiansen's book, especially the chapter about color keying.

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Barend OnneweerRe: Two step keying and track matte to get rid of noise from Keylight.
by on Aug 9, 2011 at 7:30:55 am

It's Keylight's spill removal that can bring out the noise. Bypassing it (by setting the output of Keylight to Intermediate Result) can indeed introduce green edges. I use the spill killer in Red Giant Key Correct Pro and usually a bit of Lightwrap (in the same plugin-bundle) to get rid of the spill.

Raamw3rk - digital storytelling and visual effects


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Dave LaRondeRe: Two step keying and track matte to get rid of noise from Keylight.
by on Aug 9, 2011 at 3:01:10 pm

[Mitch Hardison] "I read a few threads with solutions but I don't understand. What is a two step key and how do I do it. Also how do I use a track matte to help. I tried but then it put a green line around the subject. I don't know what I'm doing."

I probably was involved in those threads, and all I can do is reiterate what I wrote earlier. I'll try to simplify it:
  • Add the footage to the comp and duplicate it. Turn off the bottom layer's visibility.
  • Add Keylight to the top layer. Using the Status view, get a good key: solid at the core, gray at the edges. Don't worry about the noise in the key when you look at the final result.
  • Turn the visibility of the lower layer back on. Use the upper layer as an Alpha Matte for the lower layer.
  • If you get green spill, add Keylight to the lower layer, but play with its settings until the chroma key background looks washed-out. You're not creating transparency by keying, you're just using Keylight's spill suppressor.
Now -- you can't use Keylight intuitively. You have to read the instructions, or at least watch a few Keylight tutorials. If you don't know that an Alpha Matte is one of the four kinds of Track Mattes in AE, you need to read up on it because it really is AE 101:
http://help.adobe.com/en_US/aftereffects/cs/using/WS3878526689cb91655866c11...

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Mitch HardisonRe: Two step keying and track matte to get rid of noise from Keylight.
by on Aug 9, 2011 at 10:00:22 pm

Thanks so much guys! I'm trying now


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Sam CucherRe: Two step keying and track matte to get rid of noise from Keylight.
by on Oct 2, 2011 at 8:53:37 pm

Hello
Thank you for the helpful techniques you've described here.
I've been getting very nice clean masks using this two step/track matte approach, but I've run into a problem that I can't figure out.
I'm trying to pre-render the masks without the background so I can add other effects and also use them in other comps but whe I pre-render them I only get a black screen. I've noticed that in my comp window, if I turn off the background layer my masked figure disappears (that is, the duplicate layer at the bottom that uses the alpha channel of the top layer which has the keylight). What am I doing wrong?

When I pre-render I'm using Animation RGB+Alpha in my output module to preserve the alpha channel.

I really need to be able to pre-render the masks without the backgrounds

Any help on this would be really appreciated.
Sam


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