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Can't get green screen and alpha channel combination to work in FCPX

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Robert Esmonde
Can't get green screen and alpha channel combination to work in FCPX
on Nov 27, 2015 at 4:11:22 pm

I’m having a problem getting an Alpha channel video file to work in Final Cut Pro X 10.2.2.

I have a subject in front of a green screen which I’m keying over a video file of virtual TV studio background. That key works fine using the FCPX keyer.

But within that TV Studio background is a large screen TV into which I want to key a still frame. The source virtual TV studio file came from a ‘Footage Firm’ DVD and it was in .PNG codec. The virtual sets are described as containing ".. a transparent alpha channel’ into which videos can be dropped.

I’m fairly new to FCPX and to keying, so maybe I’m missing something critical. But I can’t get anything to show in the ‘transparent Alpha channel’.

I have the subject layer keyed over the virtual set and the still image file below that. But it doesn’t allow any of the still frame to show. I’m not sure if that’s the way the alpha channel should work. I checked on FCPX’s compatible codecs and PNG was not in the video section so I also tried converting the file to a ProRes 444 file, which I understand does support alpha channel. I tried it as the original PNG file and with the file converted to ProRes 444 and neither work.

I also tried dragging the FCPX ‘keyer’ over the virtual set file, although I’m guessing that’s not the way it works. It just resulted in a muddy mess of a background.

I also had a look in the Inspector at the Info/Settings/Alpha Handling and tried all three options with both virtual studio files without success.

What am I doing wrong?

Thanks!


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Noah Kadner
Re: Can't get green screen and alpha channel combination to work in FCPX
on Nov 27, 2015 at 5:32:24 pm

Can you send a screenshot or two- hard to visualize precisely what's not setup correctly here.

Noah

FCPWORKS - FCPX Workflow
FCP eXchange - FCPX Workshops


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John Rofrano
Re: Can't get green screen and alpha channel combination to work in FCPX
on Nov 28, 2015 at 3:16:38 pm

[Robert Esmonde] "I’m fairly new to FCPX and to keying, so maybe I’m missing something critical. But I can’t get anything to show in the ‘transparent Alpha channel’. "
PNG is capable of containing an alpha channel so continue to use the PNG background.

If the virtual TV background is on the primary storyline, drop the clip that you want to show through the alpha channel above it and go to the Video tab and under the Compositing group, change the Blend Mode to Behind. This will composite the clip behind the virtual TV background and it should show through the hole created by the alpha channel in the PNG.

~jr

http://www.johnrofrano.com
http://www.vasst.com



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Robert Esmonde
Re: Can't get green screen and alpha channel combination to work in FCPX
on Nov 28, 2015 at 4:23:04 pm

Thanks very much Noah and John.

Noah, I can't post the images at the moment for privacy reasons, but I'll try and clear that or show an equivalent green screen/alpha combo.

John, I tried what you suggested but I'm afraid it didn't work. Nothing showed through the supposedly alpha channel black area of the virtual TV screen. I wasn't absolutely sure which of the two clips you meant me to set to 'Behind' so I tried both options separately and neither worked. The virtual studio file is imported from the source DVD and is showing as PNG in the Info panel. So I must be missing something. BTW in my project the subject is in the primary storyline and the studio background is below it, but I tried it as you suggested with the virtual studio in the primary storyline without any luck.

But, I did find a workaround which solves my immediate problem. I just shrank the still image into the virtual studio TV screen and created a new background image over which I can green screen the subject.

Clearly I've a lot to learn about all this, but thanks again for your help.


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John Rofrano
Re: Can't get green screen and alpha channel combination to work in FCPX
on Nov 28, 2015 at 4:55:09 pm

[Robert Esmonde] "I tried what you suggested but I'm afraid it didn't work. Nothing showed through the supposedly alpha channel black area of the virtual TV screen."
It sounds like FCP X isn't recognizing the alpha channel in your PNG clip.

Try this:
  1. Select the PNG clip
  2. In the Inspector window select the Info tab
  3. At the bottom of the Inspector window change the dropdown in the lower left to Settings mode
  4. Check that the Alpha Handling is NOT set to "None/Ignore Alpha"! (if it is change it to Straight)
That will make sure that if there is an alpha channel in the PNG that it will be recognized by FCP X.



~jr

http://www.johnrofrano.com
http://www.vasst.com



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Jeff Kirkland
Re: Can't get green screen and alpha channel combination to work in FCPX
on Nov 28, 2015 at 8:39:57 pm

We're talking about a PNG still here so I'd go one step further back than John's suggestion. If you open it in something like photoshop, does it actually have an alpha channel? If yes and FCPX just isn't seeing it, try resaving it.

If you put the clip on the timeline without the chroma key clip above it, and put another clip below, does it work? Of so, make a compound clip of that, then use the compound clip below the chromakey clip.

Another possibility would be to open the png in Motion, check transparency is working, then publish it to FCPX as a generator.

Jeff Kirkland | Video Producer | Southern Creative Media | Melbourne Australia
http://www.southerncreative.com.au | G+: http://gplus.to/jeffkirkland | Twitter: @jeffkirkland


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Bret Williams
Re: Can't get green screen and alpha channel combination to work in FCPX
on Nov 29, 2015 at 10:09:27 pm

Why not just turn on the checkerboard background in X so you know what's transparent and what is black? It's in playback settings.


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Robert Esmonde
Re: Can't get green screen and alpha channel combination to work in FCPX
on Nov 30, 2015 at 10:50:32 pm

Hello Brett.

I didn't even know that was a possibility. I'm really fumbling my way around FCPX. I'll try your suggestion tomorrow.

Thanks for your help.


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Robert Esmonde
Re: Can't get green screen and alpha channel combination to work in FCPX
on Nov 30, 2015 at 10:49:00 pm

Thanks Jeff.

They sound like very good suggestions especially the one about Motion. I'll give that a try tomorrow. Unfortunately it's not a PNG still. It's some moving images of a TV studio background. I did try just using the PNG file without any chroma key but it didn't work either. I'm going to check on John's suggestion too and see if maybe the Alpha option is set incorrectly.

Regards.


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