FS5: Green Screen Advice

M

mitchino

Member
I've got a small chromakey job next week using my FS5, shooting brightly coloured hairy puppets against green screen, and one against blue.

The end delivery format is HD. Im wondering about the best settings to use, am I right thinking I would be best shooting in 4K and conforming to HD timeline to get more detail but still be 10 bit?

What about colour? I'd like to keep it REC709, is that ok or should I be shooting LOG?

What about shutter speed? is 1/50 ok? (shooting PAL 25fps).

Anything else to be aware of?
 
mitchino said:
I've got a small chromakey job next week using my FS5, shooting brightly coloured hairy puppets against green screen, and one against blue.
The end delivery format is HD. Im wondering about the best settings to use, am I right thinking I would be best shooting in 4K and conforming to HD timeline to get more detail but still be 10 bit?
What about colour? I'd like to keep it REC709, is that ok or should I be shooting LOG?
What about shutter speed? is 1/50 ok? (shooting PAL 25fps).
Anything else to be aware of?
Click to expand...

Hi Mitchino,

I'm just finishing post on a commercial that relied heavily on green and blue-screening. Here are my pointers based on that experience:

- Definitely shoot 4K and downscale if you have the option. Am I right in thinking that with the FS5 you have to choose between 4K 8-bit and 1080 10-bit? If that's the case I think it depends on how 'hairy' the puppets are. The 4K will help with getting a nice detailed key of their hair against the BG, BUT the 10-bit will also be very helpful in getting an accurate key that doesn't need too much masking to clean it.

- I stayed in Slog3 for my greenscreens and it worked out well (easy match with the rest of the footage), IMHO thanks to careful lighting and separation between subject and screen. IF you decide to go 4K and have to go with 8-bit then you'll almost certainly get better results in REC709 than in log, because the lower bit-depth will make log more prone to banding (especially in the screen).

- SHUTTER SPEED is VERY important. It depends slightly on your clients preferences/spec, although IMO puppet-shows won't be too bothered if something has the 'cinematic' cadence (or motion blur) provided by a 180-degree shutter (1/50th in your case). I say it's important because I shot several variations of my G/S element, at 180, 90 and even 45 degree shutter (equivalent to 1/50th, 1/100th, and 1/200th sec). In the end I used some of those with 1/100th and some with 1/200th. Those at 1/50th were VERY challenging to key, because I was filming a flip-book with fast moving white pages which were very vulnerable to blurring with the screen. If your puppets aren't moving too much or too fast then you might find 1/50th works OK, but I would warn you to be VERY careful about motion-blurred FG elements. If you can then test in advance, and if you can't then I'd set aside an hour at the start of the shoot to test different shutter options, bring the files into some comping software, and CHECK that they will work as expected.

- That brings me on to DOF. I would recommend stopping-down your aperture to make sure that ALL of your FG subject is SHARP. If you go wide-open and have more distant hairs falling out of focus, you WILL struggle with the key on those areas, and it might make your whole shot hard to use. Remember the especially when the director says "Oh yeah, and can we just quickly jump in for a close-up on the puppets face?" ALARM BELLS should ring, and you should crank the lights and stop-the-f*&k-DOWN!

Bottom line is all of the above is basically tweaking technical details. What WILL make or break your ENTIRE shoot is LIGHTING. Spend enough time at the beginning (ideally with a waveform monitor) making sure your screen is absolutely EVENLY lit, then (and only then) have a subject 'sit in' (easy with puppets - they don't complain too much ;-), and light them separately, making sure to avoid shadows on the screen. Every minute spent working with lighting could save you (or someone else if you're lucky) HOURS in the edit.

Hope that's all useful information, and that it goes well for you - post us some shots of the results!

Cheers,

jason
 
jasonbrooks said:
- Definitely shoot 4K and downscale if you have the option. Am I right in thinking that with the FS5 you have to choose between 4K 8-bit and 1080 10-bit? If that's the case I think it depends on how 'hairy' the puppets are. The 4K will help with getting a nice detailed key of their hair against the BG, BUT the 10-bit will also be very helpful in getting an accurate key that doesn't need too much masking to clean it.
Click to expand...

Even though it's 4:2:0 ?
 
I disagree with a lot above. Shoot HD because it is 10 bit. 10 bit will key better than 8 bit and you are delivering in HD so you don't need 4K. Don't shoot S- Log because you are wasting "data" - this is a controlled lighting shoot where you don't need 14 stops of DR, so don't waste the data on highlights and shadows that aren't there. Cinegamma 1 is the same as Hypergamma 4 and that is what you should use. (If you had the equivalent of HG8, you could use that, but you don't.) Light the green one stop under the foreground, around 50% on your waveform and make it even without shadows from wrinkles. Give your subject a bit of an edge or backlight and bump up your shutter speed 2x "normal" of 180 degrees. Shoot progressive and make your shutter speed ~ 4X your frame rate. If shooting 30P, make the shutter speed ~ 100th. Shoot at native ISO and don't shoot with your lens wide open. Shoot a 2.8 - 5.6 if possible, just not wide open and not 11-16. Turn off detail. White balance where your subject will be with the green screen lights off.
 
Thanks folks, I have lots of green screen lighting experience, that's not a problem. I'm sure I read somewhere that if you scale down 4k 8bit to HD, it becomes 10 bit.

I found this site with downloadable FS5 green screen footage, and tried the HD and 4K Rec709 clips in FCPX. The 4K produced a better key for me.

I'm going to run my own test before the shoot.

The sample footage the client supplied from their last green screen shoot is pretty rough, whatever I produce will greatly exceed their expectations I think.
 
gkantziper said:
I disagree with a lot above. Shoot HD because it is 10 bit. 10 bit will key better than 8 bit ...... Don't shoot S- Log because you are wasting "data" - this is a controlled lighting shoot where you don't need 14 stops of DR, so don't waste the data on highlights and shadows that aren't there.
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+1
Would you rather 10 bit for keying over 8 bit is like asking does 1+1 = 2 ?


Focus on lighting it well and the settings you pick in camera won't be nearly as important.
I'd take 8 bit 420 professionally lit over 10bit 422 horrible done.
 
More suggestions -
I'd vote for the 4K and stay in 4K as long as possible. Do your keying in something better than FCPX - such as Resolve / or maybe use Boris Effects? / or even premierepro/aftereffects?
use edge lights and back lights that have a bit of 'counter-acting' color - such as 1/4 minus green when doing the green screen, and 1/4 CTO for Blue screen. Make sure your back and edge lights are soft (so they 'wrap' around the fuzzies of your 'cast.' You can also add a bit of color 'enriching' gel on the lights illuminating the screen - such as PlusGreen for lighting the green screen. Of course make sure that none of this hits your subjects!
If you have any contrast issues, use cinegamma (3 or 4?) to help control highlights. I'd stay away from LOG.
shooting at 1/100th shutter should help keep motion edges cleaner. I agree with others about wanting a solid amount of DOF.
 
As a VFX supervisor, I say hire a vfx supervisor. If not:
Shoot a test!
Nuke, Flame, or even aftereffects will pull a better key than any NLE. Fusion is free and is better than NLE's.
Even 8 bit 4k is better because it gives you more samples per final HD pixel. Shoot RAW and you get the best of both worlds. Compare a 4k comp that is downscaled to downscaling before comping.
Movies are all done in LOG and professional tools are tuned for that.
Turn in-camera sharpening all the way down.
It's best if your green screen is out of focus. A good keyer will give you the texture of the screen. You don't want a cloth texture on your background.
Send it to a VFX pro for final compositing. People who do this every day will be much quicker than you.
Good Luck.
 
Don't be afraid to shoot standard gamma. If your highlights are controlled and you don't need the additional compression then you are putting more data in the picture with standard gamma ( usually std 5) and frankly faces usually look better because its very easy to get subtle unpleasing compression in the hotter parts of the flesh tones with cinegamma. Cinegammas are actually designed to be underexposed one stop. IMHO std gamma gets a bad rap on these pages from people who don't know how to use it and likewise log is abused by people who think its a panacea for lousy lighting. By all means use cinegamma if needed but usually green screen shots allow great control over lighting. It is an issue of course is you are intercutting with log footage though.

Interesting about 4K 4:2:0 vs HD 4:2:2. I'm not an expert but have been reminded in the past that this is a ratio and the higher data you start out with you may still have more information from the 4K at 0 than HD at 2. But that's just a thought- I'm not an engineer.
 
I think 4k is better because it's 100mb/s instead of 50mb/s. It's more data. When you take 4 eight bit pixels from UHD and average them into 1 pixel in HD, the precision is greater. I believe Convergent Designs thinks that their UHD>HD is superior to recording HD directly for that reason. Feel free to test...
 
As a vfx I suggest going for the largest bit depth and least amount of compression. Resolution is not as important as either one of these factors.
You're better off with 10bit HD, than 8bit 4k.

Make sure the shutter angle matches what the BG was shot on or you may have a temporal disconnect.

Use a real compositing package and keyer. Nuke, Flame, Fusion with something like Ultimate, Keylight, IBK, Primatte etc.

Some people like to light the green screen 1/4 - 1/2 stop under key, but do some testing if possible.
Don't shoot blonde people on a green screen, but use blue instead.
 
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"Don't shoot blonde people on a green screen, but use blue instead"

Interesting - never heard that before. How come - better color contrast? I always like to shoot blondes with Lee 212 ( very light yellow) on the backlight and that might help with either.
 
LennyLevy said:
"Don't shoot blonde people on a green screen, but use blue instead"

Interesting - never heard that before. How come - better color contrast? I always like to shoot blondes with Lee 212 ( very light yellow) on the backlight and that might help with either.
Click to expand...

I should rephrase that. It's my personal preference. Better separation, as they are almost complimentary colors. Heavy green spill on blondes tends to just blend the two colors together. The main drawback to the blue screen is that the blue channel is the noisiest, so having a low noise sensor helps. (Go Sony!)
But then again people pulled blue screens on film, so it can be done. :-)
 
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So some people say under expose the screen others say over..? one of these must be wrong or "not as good" from a tech stand point no..?
 
I've never keyed XAVC so I don't know how the edges hold up over say ProRes, compression artefacts are the main enemy not bit depth as they posterise the image data so in this case I would shoot 4K even if that meant going 8 bit on the FS5 as the output is to be HD the resolution will trump bit depth. The success of the key will be down to the compression and I don't know how well XAVC-L holds up if at all.

Definitely shoot REC709, if you're lighting the scene correctly there's not enough dynamic range to make shooting Log a sensible option especially in 8 bits.
 
OnSet said:
Do your keying in something better than FCPX - such as Resolve / or maybe use Boris Effects?
Click to expand...

The Keyer in FCPX is excellent and much underrated and is easily a match for Resolve.

However Keying is much better done in a VFX package like Fusion or NUKE for the ease of making holdouts and garbage mattes.
 
Harry Lime said:
But then again people pulled blue screens on film, so it can be done. :-)
Click to expand...

As I recall from 'back in the day,' Blue was a pretty strong layer in the Kodak film stocks. (I think this was particularly true with 5295 - which as I recall was optimized for Blue Screen...)

As to other comments about exposure, I've personally stayed in the 50-55 IRE range for most green screen stuff. My guess would be that the people talking about wanting to underexpose have had issues with too much 'spill' bouncing back off the screen. If you're doing a controlled medium shot (or in this case puppets) just make sure you have plenty of distance from the screen, and enough properly colored backlight and back-edge light to overpower the spill. Of course if you're doing head-to-toe walking shots it gets a lot trickier. Watch out for those shiny black shoes! And bring white sheets or foamcore to cover any painted green areas not seen in shot.

One other trick I haven't seen mentioned for lightweight cloth backdrops is to use two layers (or a similarly colored fabric behind. Many cloth colored backdrops are thin enough that they benefit from color behind them. (Green felt from a fabric store can work great behind the cloth...)

Of course testing in advance is great, but if you have to wait til you get to set, having a laptop on set can give you a quick testing capability. We usually test in Premiere since it's quick and easy...
 
Just discovered that I if I buy myself a UHSII SD card, I can record 4K 10 bit 4:2:2 ProRes to my Black Magic 7" Video Assist!

So that's the dilemma over HD and 4K sorted out, will definitely shoot 4K ProRes and conform to HD.
 
BTW - Does anyone know if I can read a UHSII card using the SD reader in a 2011 iMac? I know it'll be slow, but as long as it's backwards compatible I don't mind.
 
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