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Is there a way to Key Transparency?

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Scott Johnson
Is there a way to Key Transparency?
on Apr 13, 2014 at 1:47:55 am

I have a video in which the subject is between two different shade of green. One green is deep blue green, and the other is brownish yellow green. When I use Keylight to remove the deep blue green, the browns and yellows of the brown/yellow green remain. However, those pixels containing the brown/yellow are transparent.

What I want to do is key out any pixel that is not 100 opaque, and any pixel that holds no transparency will be visible. This would essentially provide the ability to key out anything that has any green in it, when would make the quality of any green screen irrelevant (even a natural green screen like my video)

Is there a way to do this? How?


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Darby Edelen
Re: Is there a way to Key Transparency?
on Apr 13, 2014 at 3:21:31 am

The clip black property of keylight will do this if you increase it to near 100.

I don't think this is really what you want to do. I can promise you that you'll end up with poor edges and holes in your subject. It's a given that some of your subject is going to be partially transparent when initially keyed.

Darby Edelen


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Scott Johnson
Re: Is there a way to Key Transparency?
on Apr 14, 2014 at 10:25:31 am
Last Edited By Scott Johnson on Apr 14, 2014 at 10:26:12 am

http://forums.creativecow.net/readpost/2/1050140

Thanks for the reply. The above forum contains information on the video in question that I am trying to edit. I think what I am saying is, why should a green screen or green background have to be near perfect for it to be used easily, quickly, and effectively. If you check out the video I am trying to edit, I don't see a non-rotoscope way of doing this easily at all. But I figured if you can simply extract all pixels that utilize the green channel at a particular level, then that (along with feathering) might be an effective tactic and you follow it up with deletion of transparent pixels.

I could be wrong, but I'd really like to know a fast way of editing this without rotoscoping (or roto brush tool).

Scott Johnson


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Darby Edelen
Re: Is there a way to Key Transparency?
on Apr 15, 2014 at 5:21:09 am

[Scott Johnson] "The above forum contains information on the video in question that I am trying to edit. I think what I am saying is, why should a green screen or green background have to be near perfect for it to be used easily, quickly, and effectively. If you check out the video I am trying to edit, I don't see a non-rotoscope way of doing this easily at all. But I figured if you can simply extract all pixels that utilize the green channel at a particular level, then that (along with feathering) might be an effective tactic and you follow it up with deletion of transparent pixels."

Chroma keying relies on the differences between the Red, Green and Blue components to generate an alpha. When keying Green the ideal screen is one where the Green component is brightest and there is a large gap between it and the Red/Blue components in the screen.

The grass in your image has more Red than Green in it. That's immediately problematic. The changes in luminance across the trees in the background also correspond to a smaller gap between the Green and R/B components.

This is not a situation in which chroma keying will be particularly effective. You can create transparency from this image using keyers, but it likely won't look good.

Darby Edelen


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Scott Johnson
Re: Is there a way to Key Transparency?
on Apr 15, 2014 at 3:07:50 pm

Ok, well did you also get a chance to read the "Noise Removal" idea I posted in the other thread? Essentially instead of keying chroma it's keying patterns (ie: get sample of "grass pattern" then delete all such patterns in the scene. Chroma will play a small part of this, so the grass pattern of the shadow area will be partially deleted without fully deleting the shadow. And of course a feather option would apply for smoothness).

I don't know if After Effects can identify/key patterns within an image. But if it (or a 3rd party plugin) could, then that would greatly simply this process.

- Scott

http://ytkidsvids.tumblr.com/


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