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Keying problems with the colors blue & yellow

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Melissa EvansKeying problems with the colors blue & yellow
by on Jul 25, 2012 at 4:58:42 am


I'm having problems keying out some green screen footages. Here's the gist of it:

- The footage contains a character wearing colorful clothes, but without any green in it. The colors include: red, white, purple, yellow & blue.

- I've applied keylight to the footage and the problem is, either the yellow or the blue parts will turn transparent. I suppose this is because they both make up the color green? I've tried adjusting the screen balance to about 28 so that both the blue and yellow won't be totally transparent, but I can still see through them to the background behind..especially when something moves in the background

I also played around with the clip black and clip white settings. Lowering the clip white made the yellow & blue parts not transparent, but then I get A LOT of grain and noise, and a lot of ugly green edges around the hair (which happens to be white color). Then I tried using the screen shrink to get rid of the edges, but that made my yellow & blue parts disappear as well, and the edges become very rough/jagged.

Is there any way to work around this problem?

- Also, another problem I'm having is that, when the character moves, like say, waves his hand for example, there's also these green edges around the hand. How do I go about getting rid of that?

Thanks in advance!

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Darby EdelenRe: Keying problems with the colors blue & yellow
by on Jul 25, 2012 at 6:21:23 am

You'll probably have to set up at least 2 keys. Try and preserve the yellow in one and the blue in the other. I believe the screen balance is the primary way you'd influence that.

I think the Alpha Bias control may also help, but it's more of a brute force method. You would select the blue or yellow portion (what you want to keep) for the alpha bias and then adjust the saturation until it looks ok.

For the green spill you should choose a despill bias in the range of your subject's skin tone. Adjust the saturation of the color to try and get a good result. You can also try to use other despill methods like a targeted Hue/Saturation adjustment or the Keying > Spill Supressor effect if you get desperate.

Darby Edelen

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Melissa EvansRe: Keying problems with the colors blue & yellow
by on Jul 25, 2012 at 5:05:54 pm

Thanks for the reply man! I'll be sure to try that. Hope it works!

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