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Alpha Channels/Green Screen on FCP7

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Oscar Gotti
Alpha Channels/Green Screen on FCP7
on Dec 6, 2012 at 11:58:50 am

Hello,

I have finished editing a promotional video for a production house and all we need now is to put the graphics on, this is where our problem lies...

We received:

- A clip of the graphics, with green screen revealed when the graphics "slides" over to reveal the video clips in the promo (the "fill"?)
- A clip of the same, but in black and white with the graphics in white. (The "matte"?)

We have tried using the graphics just using the "fill", also tried using both the "fill" and the "matte" using the 'chroma key', 'primatte RT' and the 'travel alpha' comp. mode but with everything we've tried we always end up with a green outline residue from the green screen on our graphic as it slides over...

Could you possibly give me a step by step guide to how we could get rid of this green residue, and how to use these elements properly?

Thanks!

Mayto


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Neil Patience
Re: Alpha Channels/Green Screen on FCP7
on Dec 6, 2012 at 3:05:22 pm

Hi
The graphics people have given you two options in one perhaps slightly confusingly. Since they have provided you with a matte then the green screen part is redundant. If you use the green screen then the matte is redundant.
I would say the matte might give you the cleanest edge so the way to do that is as follows.

You need 3 video layers. On layer 1 you have your finished background video. On layer 2 place the matte. On layer 3 place the graphics fill.
Then on layer 3 right click and select composite mode Luma.
You then should see the graphics superimposed over the background. Obviously you need to sync the matte and fill layers 2&3

The alternative is to ignore the matte and use a chroma key on the green. Maybe additionally try the green spill suppressor to clean up the edge but that can be a little harsh sometimes and needs a little tweaking to avoid a visible edge.

Go for the matte option first see how that plays out.

best wishes
Neil
http://www.patience.tv


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Oscar Gotti
Re: Alpha Channels/Green Screen on FCP7
on Dec 6, 2012 at 3:50:50 pm

Hiya,

I put all three layers on top of each other like you said and used the Luma keyer but it doesn't seem to work... the background video appears where the graphics should, with the green everywhere else..

Do you know where I can find the green screen suppressor?

Thanks


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Neil Patience
Re: Alpha Channels/Green Screen on FCP7
on Dec 6, 2012 at 4:09:47 pm

Hmm OK - just checking when you say you used the Luma keyer that you used the comp mode travel matte luma and not the luma keyer from the effects menu.
(Obviously you select that on layer 3 which should be your graphics fill)





If you did the above and your key is inverted, ie as you are describing where its "back to front" Then you need to invert your matte to make the white parts black and the black parts white. You can do this by applying an effect to the layer 2 matte. In the video filters select "channel" and in there should be "invert"
Apply that to the matte layer and it will reverse the key. Will need a bit of rendering but otherwise you should be fine.
Hope that works.

best wishes
Neil
http://www.patience.tv


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