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Old January 18th, 2014, 03:40 PM   #1
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Getting better keys

Hello people. Over the past year I have started to do these occasional edits where I am dealing with greenscreen/compositing. Simple talking head, sitting or standing, talking against a screen.

I would like to be able to pull better keys. Problems I'm having (not always at the same time, across different shoots) are jagged edges when matte is choked down enough for green to be gone, slight black or white outline usually around shoulders/body that can't be gotten rid of without degradation to everything else, generally edge issues.

These are shot by a professional crew with an EX-1 (sorry, not with the Ki whatever that allows 4:2:2, just the stock CODEC via SxS cards, not my call).

I've tried several keying plugins (trying to stay in FCP rather than deal with After Effects/Motion), like PHYX, Keylight, DVMatte, and Primatte RT. I've gotten OK results with all of them but zoomed at 20% I can see the issues I describe, and they're slightly visible even at 100% so I think more can be done.

I've read around and seen the advice that a) most tools will work, it's more about the methodology, and b) you generally can't get a good key in one pass/instance of a plugin; it's all about multiple instances doing different tasks, and multiple mattes composited into one.

These are (so far) corporate videos for the web/computer/intranet viewing, with tight deadlines, so I really don't want to get into multiple mattes and all that unless it's way less complicated and time consuming than it sounds. However, two passes of a keying plugin I can work with.

Can anyone advise, using the plugins mentioned above, or stock tools in FCP? Thanks. Not having luck finding really good tutorials online/youtube. One tutorial mentioned using two layers of the original video, one on bottom has the green desaturated and is combined with the keyed layer to somehow make the key better. . .not sure how to do that in FCP.

Thanks.
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Old January 19th, 2014, 07:00 AM   #2
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Re: Getting better keys

FCP, Premier Pro, Avid and Edius have excellent green screen keyers as they stand. If you are having to resort to elaborate keying methods, then probably the lighting and/or the distance from the subject to the green screen was probably at fault. Check some of the posts on this forum about lighting for green screen.
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Old January 19th, 2014, 02:09 PM   #3
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Re: Getting better keys

Agreed, please post more details about settings you're using, screenshots so we can see how good or bad the lighting is, etc...

for instance, if the lighting is poor and the screen even, a garbage matte should be used to get rid of most of the surrounding area. or use the smooth screen plugin
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Old January 19th, 2014, 02:10 PM   #4
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Re: Getting better keys

I promise, guys, lighting/shooting aspect was fine. Professional crew, good/even lighting, good distance from subject to screen, etc. I can't send screen shots 'cause client is corporate, very security conscious, don't want to put anything on a public forum. Only thing we could have done better (from reading around) is using one of the methods to get 4:2:2 out of the EX instead of the stock codec. It's the edges where key meets person that are giving me issues, everything else keys fine. But I'm pretty sure the problem's with me.


Anyway I found this series of very extensive tutorials (like 45 minutes here!) for a three pass keying method so I'm going to try this. Seems like it would work with any keyer (not just keylight), may be able to do it without leaving FCP (instead of going into AE like they do).

VIDEO TUTORIAL: Procedural Chroma Keying | Mediagoo:::Home of Brooksby Melton College Media Department
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Old February 15th, 2014, 10:00 AM   #5
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Re: Getting better keys

Josh, are you involved with the production of the actual shoots? I'm with Guy on this. To avoid issue in post with keys requires dealing with spill in acquisition. I ensure that a third set of lights is used to handle spill directly, and I run a few test samples and edit them on site as part of the setup. I also try to shoot uncompressed via SDI for the cleanest signal possible.

Even so, it's better to run your key in layers/passes (precomposing in AE, or using nested sequences in Premiere, etc.). vs a single all too aggressive key, (which why shooting in 10bit SDI uncompressed helps).

As you say, the issue could also be with you (as in being too picky and seeing things on the pixel level). You're quest for Hollywood results might be overkill if your final shot winds up on a website and the downrez masks the issue to begin with, (test for that before going nuts).
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Old February 15th, 2014, 01:50 PM   #6
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Re: Getting better keys

It's really hard to give advice without examples. Tell me: how does this key stack up to your personal expectations?



It was quick and dirty, 4:2:0, single pass, and quite aggressive too. In other words, with more finesse, it could be even cleaner. So how does it compare to the problems you have been having?
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Old February 15th, 2014, 04:40 PM   #7
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Re: Getting better keys

I am usually on the shoots though I don't edit everything we shoot.

I will push for them to light to 60% on the screen rather than 40, can't really do anything about the uncompressed vs 4:2:0 unless we use different cams (usually EX1s are used on these, no Ki pro box or whatever).

We do use the edge lights (though they aren't minus green'd) to counteract spill, but again, I insist spill isn't problem.

Maybe my expectations are too high, my client (not the end client, the producer I was working for) was happy with the key, so I guess that's all that matters.

I would be willing to look into the multi-matte process but after watching that exhausting 45 minute tutorial I linked to above, I see that his results weren't any better than mine (at the end of the tutorial, before he'd worked on the edges)!

Looks like the real magic is in edge blending. I bought fix keyer and did the best I could with it, compromising between blurry edges and get rid of that dark outline.

Another thing that really hurt on this was that I was given photos for the backgrounds, as opposed to creating a motion graphics limbo, and the backgrounds had color/luma values that really highlighted the key's flaws (strong, bright red/orange behind a guy with a light shirt in one).

I will push for a darker shirt since someone mentioned greenscreen has trouble with certain colors (pinks).

Anyway, it's fine, I guess the next one will be fine too. I don't plan on working on an X-men moving any time soon.
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Old February 21st, 2014, 03:29 PM   #8
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Re: Getting better keys

Key doesn't look too bad here just a little to sharp on the edges. Besides better software, better cameras, better recordings to help get better results there are ways to disguise the nature of the key. Blurring the background like the bench which is coming into focus and scaling it a little differently might help. I try not to shoot flat backgrounds if I am going to key someone in same way I try not to shoot an interview with a flat wall behind them.
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Old February 21st, 2014, 03:53 PM   #9
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Re: Getting better keys

Quote:
Originally Posted by Josh Bass View Post
Looks like the real magic is in edge blending
Getting a good key, and then working with the edges to get a good light wrap works wonders in selling the shot. The base key I always treat as the base matte, and from there the edges are individually adjusted depending on region and then remasked to build a composite matte which everything is then based on.

Usually there will be the primary matte which knocks out the screen, then a feathered matte which refines the edge. Finally combining the primary matte with the feathered matte to define the feathered areas independently can then be used that as a luma/alpha matte to further apply an adjustment layer to the edges to fight either spill and/or to help sell the environments effect on the subject.
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Old February 21st, 2014, 04:03 PM   #10
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Re: Getting better keys

Quote:
Originally Posted by Daniel Epstein View Post
Key doesn't look too bad here just a little to sharp on the edges. Besides better software, better cameras, better recordings to help get better results there are ways to disguise the nature of the key. Blurring the background like the bench which is coming into focus and scaling it a little differently might help. I try not to shoot flat backgrounds if I am going to key someone in same way I try not to shoot an interview with a flat wall behind them.
Thanks Daniel! I wasn't actually the one looking for advice, I was just using one of my keys to try and understand what Josh thought was wrong with HIS keys. Since he can't show us his, I thought I'd post mine and ask "are yours better or worse" to try and get a sense of what he's looking for.
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Old February 21st, 2014, 04:19 PM   #11
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Re: Getting better keys

Id still like to see a tutorial about the advanced methods youre talking about. Ive still only been able to find the one i linked to above which only takes you TO the point of edge blending. Something that shows how to do one matte for hair, another for the rest, then combine them would be nice. Either in fcp, premiere, ae or motion
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Old February 21st, 2014, 06:29 PM   #12
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Re: Getting better keys

This is a tutorial I looked at years ago when I was just starting out...


Again, this is not a keying tutorial, so don't watch if for the exact technique but it provides a good look into curling the background onto the edge of the subject. While he already has his layers split with alpha channels, imagine doing this with a well defined key and using your key as a matte.

Here is a tutorial that starts to delve into better keying techniques and edge refinement and actually pulling the initial key. The above tutorial is moreso for compositing an element together into a background.
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Old February 22nd, 2014, 08:30 PM   #13
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Re: Getting better keys

Thanks. I dont have another green screen project any time soon but will take a look at these next time i do (if i have issues---no point making life difficult on myself). I have suggested on an upcoming shoot (i dont think im going to be the one editing it) that they use an atmos ninja with the ex1 to shoot 422 and light screen to 60%.

Also have you guys experienced that certain clothing colors dont key as well as others? I dont mean the obvious like "dont wear green on a greenscreen", but this last instance where i had all the problems, talent wore a light pink shirt with a silky sheen to it. Someone i mentioned this to said could be an issue. Something something blah blah blah wavelengths?
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