4k2HD For Green Screen

C

ChadN

Well-known member
Has anyone shot green screen with the 4K2HD? I'm not sure i want to shoot in Slog2, so i'm thinking REC709 800% and exposing the screen at 50% on the waveform. Skin at around 70%. I've never used REC709 before, so hopefully i'm getting it.

Of course i'll do some tests, but wondering if anyone has any thoughts about it. I'd even be up for shooting in Slog2, but the curve is new to me i'm not sure where i'd set the green screen exposure.
 
4K RAW would be better for VFX work IMO; the more resolution the better

I think S-Log should be fine. Just bump up the curves / saturation in post. You either just have the profile baked in at the time of the shoot or after. For me, I usually prefer after.
 
4K2HD works, 2k raw would be better, 4k raw would be better than that, but heck people do green screening with the 4.2.0 8bit h264 on the 5D... not my recommended workflow, but that's what we did on an international promo for a major network. Point being, you can for sure shoot great green screen with the 4k2HD.
 
I figured 4K RAW files were too large for me right now, but i might do a test shot and see how it is. I hadn't considered 2K RAW for green screen, but that might be the way to go actually!

Thanks for the input, guys.
 
I would avoid 2K RAW for green screen. There is quite a bit more aliasing and moire in 2K RAW than 4K2HD and 4K RAW, both of which are super clean.
 
Hey Gene, thanks for the heads up. Yeah, the aliasing in 2K Raw is pretty strong. Now that i think of it, i've seen it in some test shots of buildings for sure.
 
2K Raw is a terrible choice. 4K Raw makes some sense as the extra resolution may help you key out fine hairs, but the same cannot be said of 2K Raw. Personally, if you're not finishing in 4K I would reccommend 4KtoHD in straight rec709, not slog2, not 800% rec709. You're in a studio for gods sake! Controlled lighting, it's highly unlikely you'll need the extra dynamic range/over exposure headroom slog2 and 800% so all you're doing is adding an unnecessary colour grade step in post before you key. 4K Raw is that x10 plus a headache in terms of data load and rendering! So unless you're doing something with a lot of fine hairs or edge detail then I'd avoid it.

I shot greenscreen the other day that way and it keyed beautifully. Simply beautifully. As others have shown 4KtoHD gives you a slightly higher resolution than the onboard vesion - really good fine detail.

Just make sure you have a nice even light on the screen (you can use the waveform and false colour to check this and adjust the lighting) you can expose using false colour: have the screen come out green and the highlights on the face yellow.

If you can pull the subject as far from the screen as possible (to avoid spill), add some backlight (to increase separation from the screen), shoot a little stopped down (4/5.6) so the whole of them is on focus and if they're moving a lot consider shooting with a slightly faster shutter: 1/100sec - 90deg.

Do all that and you should be laughing.
 
Wasn't aware the aliasing was that bad in 2k raw in this system as I went straight from avchd to 4k2hd, I was just saying the extra bit rate and colour space is beneficial when keying. (raw 12 bit over 422 10 bit over 420 8bit) It's not just resolution that makes it easy or hard.
 
I've just done some simple green screen work for a client last week, on-site with a Lastolite pop-up green screen lit by 2 x 2bar fluros, subject lit by 1 x 4bar fluro, I didn't have any more lights with me at the time to do a backlight on the subject unfortunately (bad move on my part!). Recorded this in AVCHD (I've yet to purchase a 7Q). It was a typical interview, half-body length, subject sat down, only decided to do green-screen at the last minute. Fortunately the guy had short flat(ish) hair and wasn't wearing any green! Got a pretty clean key in FCP, by carefully adjusting the matt feather, size and spill etc. I'll just have to assume/guess that the 7Q's 4K2HD recording would be cleaner, meaning I wouldn't have needed as much (if any) feather adjustment. But even with the AVCHD I was still happy with the end result, it must be even better with the 7Q - looking forward to getting one this year hopefully! Let us know how you get on ChadN!
 
I have been shooting green screen interviews for Warner Brothers for the past month using 4K2HD (basically 3 days after the firmware was released). When we did our initial test the editor took our footage and composited it in what he said was an "impressive one pass". In my experience if you are using REC 709 be sure to decrease your shadows as its very contrasty. I would have liked to have shot everything in SLOG2 but the editors are dealing with a massive amount of EPK footage and said they would prefer not to have to do a lot of grading.
 
Sorenson said:
Wasn't aware the aliasing was that bad in 2k raw in this system as I went straight from avchd to 4k2hd, I was just saying the extra bit rate and colour space is beneficial when keying. (raw 12 bit over 422 10 bit over 420 8bit) It's not just resolution that makes it easy or hard.
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Yet, but resolution, particularly colour resolution is a big part of it and 2K Raw has significantly reduced colour resolution compare to the 4KtoHD apple pro res, due to the pixel binning - and I suspect the clever little method CD uses to create the 4KtoHD (Mitch has been a bit vague about it, something about the luma and colour being processed differently).
 
Colinelves said:
Just make sure you have a nice even light on the screen (you can use the waveform and false colour to check this and adjust the lighting) you can expose using false colour: have the screen come out green and the highlights on the face yellow.

If you can pull the subject as far from the screen as possible (to avoid spill), add some backlight (to increase separation from the screen), shoot a little stopped down (4/5.6) so the whole of them is on focus and if they're moving a lot consider shooting with a slightly faster shutter: 1/100sec - 90deg.

Do all that and you should be laughing.
Click to expand...

I'm the primary multimedia/video person for the company I work for. They just finished installing a ProCyc green room studio for our product shoots, customer testimonials, HR videos, and such. Very sweet room indeed. However, it's taking some getting used to for sure. The green flooring and wall treatment absorbs light very well and at the same time is bright without being reflective perse. My first few times with it was horendous. I lit it like I normally would with 6 Ikan 500 LED lights. yeah, completely blew out the background. yet it didn't look that way to my eye at all. After using false color on the Odyssey 7Q to drop illumination down within the "green" range, the lights were only on about 16% power. Interesting for sure. Tests came out much better. I do have a question for Colin. You say to expose the background into the green, and highlights on the face in the yellow range. I cannot do this, for when I get proper exposer on the face, I push the background into the yellow as well. To get the background back into the green, I've got to basically almost turn off the background lights. I know the simple response would be to keep the background lights off. But, I get shadow casting a bit. The talent is about 8 feet from the corner. The ProCyc installation basically pulled out the corner with 3.5ft radius transitions where the corners meet and where the floor and walls meet. Anyway. just sharing....
 
rawnster said:
I'm the primary multimedia/video person for the company I work for. They just finished installing a ProCyc green room studio for our product shoots, customer testimonials, HR videos, and such. Very sweet room indeed. However, it's taking some getting used to for sure. The green flooring and wall treatment absorbs light very well and at the same time is bright without being reflective perse. My first few times with it was horendous. I lit it like I normally would with 6 Ikan 500 LED lights. yeah, completely blew out the background. yet it didn't look that way to my eye at all. After using false color on the Odyssey 7Q to drop illumination down within the "green" range, the lights were only on about 16% power. Interesting for sure. Tests came out much better. I do have a question for Colin. You say to expose the background into the green, and highlights on the face in the yellow range. I cannot do this, for when I get proper exposer on the face, I push the background into the yellow as well. To get the background back into the green, I've got to basically almost turn off the background lights. I know the simple response would be to keep the background lights off. But, I get shadow casting a bit. The talent is about 8 feet from the corner. The ProCyc installation basically pulled out the corner with 3.5ft radius transitions where the corners meet and where the floor and walls meet. Anyway. just sharing....
Click to expand...

One thing worth mentioning is that the FS700 should be in Rec 709 (not simply 800% Rec 709) for those exposure values to be relevant.

Anyway, to answer your question: It sounds like your subject illumination is not bright enough. Ideally you want the green screen to be a stop under key - so if, when you light the subject and expose it correctly, the green screen is in the yellow - it means that your subject illumination and back ground (screen) illumination are at the same exposure level. In this instance the options are to reduce the illumination on the background or increase it on the foreground/subject.

So... Put more light on the subject, or move the lights you have on the subject closer to them (if you can). Put them at half the distance they currently are and you should get an extra stop of illumination. Maybe you could repurpose one or two of the Ikan's to illuminate the subject rather than the background?
 
Thanks Colin. I had a shoot yesterday afternoon. It was a 3 camera setup, shooting an HR role-play training session. Exposers came out very nice. Just a quick look in post showed the green sitting beautifully in the background. A siimple eyedropper from Primatte 5 removed the green almost completely the first time. Sweet. I love it when it works. :-)
 
We shoot alot of greenscreen with 4K2HD ProRes Slog2 with fantastic results! Before 4K2HD, it was an absolute nightmare...
 
rawnster said:
I'm the primary multimedia/video person for the company I work for. They just finished installing a ProCyc green room studio for our product shoots, customer testimonials, HR videos, and such. Very sweet room indeed. However, it's taking some getting used to for sure. The green flooring and wall treatment absorbs light very well and at the same time is bright without being reflective perse. My first few times with it was horendous. I lit it like I normally would with 6 Ikan 500 LED lights. yeah, completely blew out the background. yet it didn't look that way to my eye at all. After using false color on the Odyssey 7Q to drop illumination down within the "green" range, the lights were only on about 16% power. Interesting for sure. Tests came out much better. I do have a question for Colin. You say to expose the background into the green, and highlights on the face in the yellow range. I cannot do this, for when I get proper exposer on the face, I push the background into the yellow as well. To get the background back into the green, I've got to basically almost turn off the background lights. I know the simple response would be to keep the background lights off. But, I get shadow casting a bit. The talent is about 8 feet from the corner. The ProCyc installation basically pulled out the corner with 3.5ft radius transitions where the corners meet and where the floor and walls meet. Anyway. just sharing....
Click to expand...

Like colin said, you need to adjust your lighting. Our cameras are so sensitive that we are used to just opening up to make things brighter, but with green screen you need to start by picking your aperture/camera settings. Lock it. Then light your green screen to the proper IRE. From there, you need to add lights for your subject to get them to the exposure you want (purely with lights, no adjusting camera settings).
 
In moving into this new studio, I've had to re-learn some things. For instance, in the old studio, I was lighting a green screen drop cloth with tungsten lights. Two 1000watt lights with soft boxes. This seemed to work fine, in that I didn't have an issue pulling the key in post. Now with the new setup and a butt load of new LED lights, things change. I'm now lighting the green background with daylight balanced LED lights. I like the way they light the green background, but need to back off my illumination quite a bit. ProCyc's paint is specifically illuminate. As Colin mentioned, I moved several of the LED lights from the background, and use them to light the talent. I don't like the "look" of these LED's on the talent, so I've added some cto gels to the lights to warm things up a bit. Much better.

To address Josh's comments: I don't adjust the camera to compensate for exposure. I set the f-stop at around 4.5f to capture what I'm filming in focus; and, no added gain..zero gain.
 
Whatever color balance your lights are on the green screen should be how you set your camer's color balance. Use daylight LEDs on the backdrop then set the camera white balance to daylight. Then you can choose to gel your lights on the subject however you like for visual effect.

Setting the green screen to one stop below key in REC709 is a standard way to get proper rich color saturation for a clean key. And it's always good to get the subject as far away from the screen as possible to avoid bounce back green spill onto the subject. I often will shoot greenscreen work using grid-mounted lights for the screen and stand-mounted lights for the subject. This allows me to preset the screen and then I know exactly what stop I will have on the lens. Then I just adjust the subject lights until they are lit appropriately.
 
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