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Pulling better keys

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Josh Bass
Pulling better keys
on Jan 18, 2014 at 9:11:06 pm

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 (probably on here!) 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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John Fishback
Re: Pulling better keys
on Jan 19, 2014 at 10:29:44 pm

The key to achieving a one pass green screen key is lighting the bkg properly. Otherwise, you need to apply the keyer multiple times. Motion has an excellent keyer, particularly, the newer versions, but Keylight & PHYX are excellent, too.

John

MacPro 8-core 2.8GHz, 16 GB RAM, OS 10.8.4, QT10.1, Kona 3, Dual Cinema 23, ATI Radeon HD 5870, 24" TV-Logic Monitor, ATTO ExpressSAS R380 RAID Adapter, PDE enclosure with 8-drive 6TB RAID 5
FCS 3 (FCP 7.0.3, Motion 4.0.3, Comp 3.5.3, DVDSP 4.2.2, Color 1.5.3)
FCP-X 10.0.9, Motion 5.0.7, Compressor 4.0.7

Pro Tools HD 10 w SYNC IO & 192 Digital I/O, Yamaha DM1000, Millennia Media HV-3C, Neumann U87, Schoeps Mk41 mics, Genelec DSP Monitors, Prima CDQ120 ISDN


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Josh Bass
Re: Pulling better keys
on Jan 19, 2014 at 11:12:43 pm

It was a professional shoot with a pro crew and the screen is fine, I promise (looking at it on scopes). It's pilot error.

At any rate, I got my best results with Primatte RT inside FCP, believe it or not, sent a still to client, he says it's fine. If there a problems at this point I'm going to try this three pass method next--seems like it would work with any keyer (tutorial is with Keylight/After Effects in any host:

http://www.mediagoo.co.uk/?p=202


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Mark Suszko
Re: Pulling better keys
on Jan 19, 2014 at 11:43:06 pm

What I have gotten into the habit of doing is shooting thru the lens at a macbeth color chip chart during or just after the shoot, while the camera and lighting for the chromakey effect is still set. My first step in post has been to bring up the footage of the chart, and color-correct that, using the vectorscope, waveform monitor, and the 3-wy color corrector and proc-amp filters.

Once the chart reads right, I copy/paste it's settings onto the actual green screen footage, You can see the difference right away in the unkeyed greenscreen shot, because now the green is very saturated and even-looking ...and what used to take many minutes of noodling around, becomes pretty much a one-click operation to pull a very solid key. I use the regular FCP7 chromakeyer, or Primatte. Really, it makes sense that your keys are going to work best if the footage is truly calibrated beforehand. I think too many users barely check to see if it's peaking at 100 IRE and they leave the rest unexplored.

I don't consider the internally-generated bars from a camera to be all that useful for this job: what I want to see, and what the keying software wants to see, is what actually passed thru the LENS onto the SENSOR, then got recorded. Internal bars, being generated not by the camera's image circuits, but merely played back from a memory file, may have little relationship to that footage, based on white balance alone.

Absolutely, step one is lighting the green evenly. But step two has got to be, calibrating your incoming footage to a known standard.

Macbeth charts are expensive. A standard color bar chart could also work, and they can be pricy too. But then again, so are the hours spent tweaking a key, if you have no starting point.


I will say that we just did the same setup in FCP7 and in FCPx, same footage, and FCPX's keyer blew me away by making a perfect key in one button push. The keyer in X is decidedly more advanced. We got good keys from both systems, side-by-side, but FCPX automatically tweaked the incoming footage, prior to invoking the keyed, whereas in FCP7, we did it manually using the chart.


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John Fishback
Re: Pulling better keys
on Jan 20, 2014 at 12:13:26 am

I agree FCPX's Keyer is exceptional. It's ability to adjust the key in different areas of the frame without having to add more instances of the keyer is terrific. And it works the same way with edges. You can affect different edges in the one instance of the Keyer.

John

MacPro 8-core 2.8GHz, 16 GB RAM, OS 10.8.4, QT10.1, Kona 3, Dual Cinema 23, ATI Radeon HD 5870, 24" TV-Logic Monitor, ATTO ExpressSAS R380 RAID Adapter, PDE enclosure with 8-drive 6TB RAID 5
FCS 3 (FCP 7.0.3, Motion 4.0.3, Comp 3.5.3, DVDSP 4.2.2, Color 1.5.3)
FCP-X 10.0.9, Motion 5.0.7, Compressor 4.0.7

Pro Tools HD 10 w SYNC IO & 192 Digital I/O, Yamaha DM1000, Millennia Media HV-3C, Neumann U87, Schoeps Mk41 mics, Genelec DSP Monitors, Prima CDQ120 ISDN


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Josh Bass
Re: Pulling better keys
on Jan 20, 2014 at 12:35:20 am
Last Edited By Josh Bass on Jan 20, 2014 at 1:01:16 am

Interesting. I'll see if someone has a color chart next time we do one of these shoots. I just tried applying a secondary color corrector and isolating the screen, and jacking it up in level so it's a bright green. I still got the dark outline around the guy which was my whole reason for posting, so that didn't seem to help.

Let me ask you all, where do you find you get best results as far as green screen light levels ON THE SHOOT? We've heard between 40-60% (this time was a flat line right at 40% on the FCP scopes so wondering if that's an issue).

Still with FCP 7. I have not dived into "X" yet. Very curious about it cause NOW many folks seem to love it, but their reasons all seem to have to do with metadata/tagging and all that, which doens't really fit how I edit (I work mostly on short projects with not much footage, not worth it to sort through and tag the crap out of everything vs. just scrubbing through to find the clips I want. If there's 10 takes of the same thing I assume #10 was the best and that' why we stopped!) However, good keying and color correction (I think it's gotten decent marks on those fronts?) are also intriguing. Plus I'm pretty familiar with motion now so I don't know if 5 is a huge improvement over 4 but there's another thing.

Have CS6 suite too but don't know Premiere/AE that well yet, and you know, deadlines etc.

I think on this project I've gotten a good enough result with FCP's primatte and the edges and lightwrap from the fix keyer, so I might buy the PHYX suite and go with that combo.

Also, have you guys experimented with taking the in-cam sharpening down on these kinds of shoots? As I said, EX-1 on this shoot. I'm looking at the original footage and I can still see that dark outline around the shoulders (light shirt), against the green screen. Wondering if in the future taking down the sharpening would aid with that.


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Mark Suszko
Re: Pulling better keys
on Jan 20, 2014 at 1:14:23 am

Bright is nowhere near as important as EVEN.

Indeed, making the green too bright defeats the purpose: it's a chrominance, not luminance-based key, after all. So you want it saturated, full of that oddball green color.

I tend to top mine out at around 80 IRE, brightness-wise, and I light my talent separately for up to 100 IRE for a highlight. On our blue screen, I use a bastard amber gel backlight to help kill spill. On green, you'd use a magenta backlight, especially on the hair.

The compensating filter plug-in on your keyer is simulating that light by adding magenta where it sees an edge. We now own an LED color PAR by American DJ, on which you can dial in specific colors so that might also get used some day.

Spill and shadow should never be an issue if you have the right distance separating subject from screen, and light them separately. My rule of thumb for distance from the screen is twice the subject''s height as a minimum.


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Josh Bass
Re: Pulling better keys
on Jan 20, 2014 at 4:30:32 am

As I said, screen was very even, flat line right at 40% all the way across. Distance etc. are fine. Generally we are in a large room when we do these shoots so we don't have to force them to be close to the screen.


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Tom Matthies
Re: Pulling better keys
on Jan 21, 2014 at 2:04:41 am

Stepping back a bit, I've had very good results with DV-Matte Pro but there is a definite order to go through to set everything up correctly. Using DV-Matte with FCP's matte filters or ones from the Boris should give you a very good key, especially if the footage was shot correctly. 4:2:2 is best but it still works pretty well with 4:1:1 or 4:2:0 footage.
It isn't a one step process but a progression as you work your way through the controls from top to bottom. I can normally key frizzy hair with little or no bleed through to the background.A bit of spill suppression will help. I almost never have any issues with a ragged matte especially with decent footage.

E=MC2+/-2db


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Josh Bass
Re: Pulling better keys
on Jan 23, 2014 at 3:35:24 am

This is 4:2:0. Most folks I have asked have said the screen was lit kind of low (40%), so that could be one thing. Another is the guy is wearing silky light pink shirt, was just told wavelengths something something weird interaction with the green; that may be another factor.

It's not that I can't get rid of the green around the hair, it's doing that AND still getting rid of the thin black outline around him everywhere else. . .it's one or the other. Keep the detail in hair? Black outline. Kill outline? chop into hair a little.

However, I watched an elaborate tutorial on the 3-pass method in AE, and even after all that, he still had an edge/black outline like mine (promising to tackle that in his next tutorial on edge blending). So maybe I'm expecting too much from the keying plugin (i.e. it's the keyer's job to make the background disappear, another plugin handles the integration of subject more fully into background) and it's time to investigate/learn about edge blending (though sometimes those are the same plugin).


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