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Chroma Key Problems

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Sam Hurt
Chroma Key Problems
on Oct 10, 2015 at 12:26:26 pm

Hi, first post here so hello. All my other queries in the past have been solved by simply reading other posts on the site so thanks everybody.

I've not used Chroma Key on FCP before but am editing together a project using some green screen. After shooting I did a quick test on iMovie to see if it would key properly and it worked well.

So I've edited my main video together and am now looking to add other footage into the green screens. I've followed several tutorials on YouTube and am going slowly mad.

Window panes in a room were covered (on the inside) with green screen material and people moved in front of them. The idea being that the 'outside' could be added later on.

There are two problems so far:

1. When I go to click onto the window panes with the dropper tool it keys out the white window frames (at least part of them).

2. If I try and playback after adding the second video track with the incorrect part keyed out I simply get an 'unrendered' message.

All footage has been converted to pro Res LT.

I really appreciate any suggestions


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Nick Meyers
Re: Chroma Key Problems
on Oct 10, 2015 at 10:27:23 pm

[Sam Hurt] "1. When I go to click onto the window panes with the dropper tool it keys out the white window frames (at least part of them). "

what OS are you using?
i have found that with Yosemite, FCP's eyedroppers don't work anymore.
you have to find the colours manually
there's a small key icon ion there that will switch the image around to just the key
working in that mode, and working the colour, luma, and saturation controls is pretty easy


[Sam Hurt] "2. If I try and playback after adding the second video track with the incorrect part keyed out I simply get an 'unrendered' message."

there's an RT menu top left of your timeline
set your timeline's RT playback to "unlimited"


[Sam Hurt] "All footage has been converted to pro Res LT."
this is a separate issue,
but LT, being quite compressed, is not as good for green screen work as 422 or HQ.


nick


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Sam Hurt
Re: Chroma Key Problems
on Oct 11, 2015 at 11:08:41 am

Hey, thanks for the reply.

I'm still using Mavericks here (10.9.5). I will try the other method not using the eye dropper when I get out of bed (am currently ill!)

I converted all footage to Pro Res LT (from H264) as the files are not as large as 422 or HQ. What is the best format for green screen work?

Thanks


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Nick Meyers
Re: Chroma Key Problems
on Oct 13, 2015 at 2:33:34 am

the more colour depth you can get the better it will be,
but given your source, i'm not sure how much extra will help.

HQ may not offer any improvement over 422
it may... but i don't think it will. i'm no expert in this, might be worth another post.

422 will be better than LT

obviously this would mean converting from the h264 again, not simply up-grading the LT


nick


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Shane Ross
Re: Chroma Key Problems
on Oct 13, 2015 at 2:47:01 am

[Sam Hurt] "I converted all footage to Pro Res LT (from H264) as the files are not as large as 422 or HQ. What is the best format for green screen work? "

Well, the best format for green screen starts with SHOOTING. H.264 is not the best for green screen work. In fact, it's one of the worse formats. Highly compressed, 8-bit. Good green screen starts with a good shooting format. BUT, nothing can be helped about that now...you gotta do what you can with what you got. Convert to ProRes 422, not LT. HQ is worthless...the only thing you'll gain over ProRes 422 is 50% larger file sizes.

but yeah, note that your keys won't be as clean as they can, because H.264 is just not good for keying.

Shane
Little Frog Post
Read my blog, Little Frog in High Def


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Sam Hurt
Re: Chroma Key Problems
on Oct 13, 2015 at 2:24:23 pm

Ok well thanks for all of that information. Unfortunately I didn't shoot it, I entrusted that job to someone else. Like you say, it is done now so I've just got to work with what I've got.

I did a test reconverting some footage and 422 does look better that LT and weirdly looks better than HQ which seems strange.

I am getting to grips with keying the background out using the manual controls but it does look a bit raggedy in places which is s shame. Some mistakes here that I won't make again!


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Dave LaRonde
Re: Chroma Key Problems
on Oct 13, 2015 at 5:08:37 pm

You may not want to use FCP for this job. You may want to use Motion. You can animate garbage masks on multiple layers to pull keys that look good in one portion of the shot, but not another.

Keying isn't always a couple of clicks and poof you're done. Sometimes it's a real pain.

Dave LaRonde
Promotion Producer
KGAN (CBS) & KFXA (Fox) Cedar Rapids, IA


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