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Green screen noise high when people wearing white or black?

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Adam Leonard
Green screen noise high when people wearing white or black?
on Jul 26, 2019 at 9:14:43 pm

Let me know if this should be on another forum.

So we're shooting with a Canon XF405, tungsten lights with lightboxes, and using ATEM as our switcher. The big problem is, when we use the green screen, the amount of visual "noise" going on in even the tiniest bit of black, white, or gray in someone's clothing is incredibly high. We tested out some new lights recently (LED), and the results are better, but it's still there. It looks like TV static crammed into the areas of clothing of those colors. I've tried tweaking the ATEM chroma key settings every way, adjusting the lights, and we'll eventually be getting a better green screen, which should allow us to try a wider range of chroma key settings.

Just recently I was reminded that some people have gray hair, so telling people to not wear white/black/gray is out. What's causing all this noise and what do I do about it?


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Chris Santucci
Re: Green screen noise high when people wearing white or black?
on Jul 27, 2019 at 12:30:32 am

I've done a LOT of greenscreen work, including post work, and even though I've never used a switcher, it sounds like either exposure is low or it's really just a settings issue with the switcher. Possibly both.

http://www.santucci-cinematographer.com


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Adam Leonard
Re: Green screen noise high when people wearing white or black?
on Jul 31, 2019 at 8:00:29 pm

Thanks for the response. I tried turning the exposure up and it looked...well maybe slightly different, but mostly the same. Like the noise is showing up at different places or something. Even tried turning the exposure up to a ridiculous level and trying adjusting it through different methods and that didn't fix it.

A weird thing I did confirm is that it depends on what's been keyed into the background. For these tests, I was wearing a gray shirt with lots of tiny black streaks on it. Had a modest amount of noise when I had the screen keyed to a plain black background, but almost none when I had it keyed to a white spreadsheet with a little bit of black lines and text. Does that mean anything?

For what it's worth, the pearl-colored buttons on this shirt get noisy with either background.


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Chris Santucci
Re: Green screen noise high when people wearing white or black?
on Aug 1, 2019 at 4:05:47 am

The plate shouldn't make any difference. A good key is a good key.

Are you sending a 10 bit video signal to the keyer?

http://www.santucci-cinematographer.com


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Adam Leonard
Re: Green screen noise high when people wearing white or black?
on Aug 1, 2019 at 6:59:31 pm

Uh, how would I know if I am?


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Mark Suszko
Re: Green screen noise high when people wearing white or black?
on Aug 1, 2019 at 7:03:54 pm

Detail the signal chain from the camera out to the switcher, and from the switcher out to the recorder and monitors. What cables, connectors, etc.

Are you using SDI cables or regular coax?


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Adam Leonard
Re: Green screen noise high when people wearing white or black?
on Aug 2, 2019 at 6:49:58 pm

Wish this forum would let me "officially" make this post a reply to both of you at once, but it doesn't look like I can do that. To answer Chris' question, the camera is a Canon XF405.

As to Mark's question: I didn't set this up myself. Did a lot of tracing cables and here's that I've figured out:

The signal starts with an SDI cable out of the camera. It then goes to Decimator MD-HX cross-converter that's mostly there to flip the image for lightboard shoots. From there it leaves via both SDI and HDMI cables, which both lead to a Blackmagic physical switcher (an ATEM Television Studio HD) , that I usually ignore in favor of the bigger and more elaborate ATEM Software Control. From there it takes an SDI cable to a BlackMagic HyperDeck Studio Mini. There is an SDI cable going back into the switcher and also an HDMI cable going into what I'm fairly certain is this model of distribution amplifier. From there it takes another HDMI cable to this model of streaming media processor from there, one HDMI cable goes through this model of distribution amplifier, and then back to the switcher and the deck with more HDMI cables. The other goes to an HDMI cable that leads to our confidence monitor. A system is set up that connects a USB port that people stick a thumb drive into with the Extron processor.

I kind of ran out of time for the workday at this point, but I just now discovered that a few of the above things are also connected via Ethernet cable via a router (I'm gonna say the media processor, the switcher, and two computers) and as far as I can tell, that includes the computer running the ATEM software.

It's really a zoo of cables back there. I started out thinking this would take 15 minutes, and it took most of the work day. About 30 minutes in I started thinking that it might be a good idea to volunteer to make a schematic of the whole thing, but now I dread the thought of doing that and would only do so if I really needed it or completely ran out of other work to do. If you need any more details, I'll be getting them by asking the person who set it all up.


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Mark Suszko
Re: Green screen noise high when people wearing white or black?
on Aug 2, 2019 at 8:29:55 pm

That seems like a lot of gak in-between the camera-out and the switcher-input to me. Each stop or inter-connect along the way gives an opportunity for signal loss and delay.

The next thing I would do, personally, is run an SDI cable direct out from the camera, into the switcher, then test the chromakey. If you don't have a long run of SDI cable handy, bring the camera closer to the switcher and use the longest you DO have, you could grab a bright green poster-board from Walgreens and make a tabletop chromakey test area in the control room if necessary. (though I'd just order a long-enough cable from Monoprice for this).

And you know in your heart, the right and manly thing to do *is* to document and diagram the system. Like insurance and writing out your living will, people put it off because it's boring and tedious, and regret it very much, later.


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Adam Leonard
Re: Green screen noise high when people wearing white or black?
on Aug 8, 2019 at 6:27:19 pm

Well, I talked to the person who set up the studio. He said that essentially, the SDI cable only goes through the Decimator box and then goes straight to the switcher. Everything else is more for after that. I think I was thinking a little too much about "connecting" it to the touchscreen version of the ATEM when I was mapping it out here.

He also says that he has a schematic of the setup that only needs minor updates. I'll post it here if I get a copy.


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Chris Santucci
Re: Green screen noise high when people wearing white or black?
on Aug 1, 2019 at 8:27:13 pm

What cameras are you using?

http://www.santucci-cinematographer.com


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