Checklist for Exterior Greenscreen Shoot on MX

[Matthew Bowyer]

Hi Redusers,

Long time reader first time poster, and am soon doing my first VFX supervisor job on a feature shoot in Japan. Very excited but a bit nervous, and have been compiling all the information possible from these forums as to everything to watch out for. Coming from a compositing background this is first time actually controlling the shots on set and want to get it right.

In terms of matching the two plates and tracking I'm pretty fine, its more my lack of experience lighting and shooting on a RED/MX that worries me.

Below is my checklist for lighting and camera, I was hoping to get some comments on it from you guys. We are shooting 5 day exteriors and 1 night exterior, using the sun to light our greenscreen during the day and daylight bulbs at night. Shooting on the Red-MX, we are replacing a background behind a balcony with the ocean (see attached pics of our rough test shoot yesterday - note we did not have RED-MX or frame for screen at this point, this is 5D but will give you an idea of the sort of shots we're doing)

My biggest question is the varying difference of opinion on whether to over or underexpose the screen for the best key. Underexposing by one stop (eg camera at f4, actors at f4, screen at f5.6) seems to be the main suggestion but I'd really appreciate your thoughts. Also since both actor and screen are being lit by the sun would you suggest adding light to actors or taking away from screen to achieve this?

Any other thoughts, suggestions, comments would be great as well.

Matthew Bowyer
VFX Supervisor
"SnowChild"

CAMERA
• Greenscreen as far away from actors as possible.
• Shallowest depth of field possible.
• No sharpening/enhancing in camera, keep clean.
• Camera at fast shutter speed (within reason) if actors making large movements.
• Shoot at 50-70IRE
• 320ASA
• 5000 Kelvin
• Keep ISO low to reduce noise 150-200 ideal.
• Shoot at 4K for best information.
• Dynamic range within less than 7stops max.

LIGHTING
• No more than 0.5stop difference at any point of screen.
• Light greenscreen using daylight bulbs. If Tungsten use 80B/C/D filter.
• Green gels could help compensate for faded screen.
• Back lighting on talent is essential to get separation between actors edges and greenscreen.

 

[Jeff Kilgroe]

You have tons of range with MX, so trying to under/over expose the screen in relation to the talent isn't going to get you very much. But you will want to make sure you have your exposure between the two controlled enough to avoid spill or green halos. The under-exposing of the screen by one stop can help here. But as always that is relative, so best to do a quick test and be prepared to pull light from the screen or add more to your talent to compensate.

As for the checklist, you have some contradicting things here. So...

CAMERA
• Greenscreen as far away from actors as possible.

Yes. To a point. At a certain distance it will no longer make any difference if it goes further back or not. You want it back far enough to avoid green bounce. That can often be tricky if you need to keep tracking marks on the screen in focus, but based on your test images, I don't think that will be a concern.

• Shallowest depth of field possible.

Why? That's a stylistic thing. Are you shooting with an f0.95 lens or just what is the shallowest DOF possible that you aim to achieve? There are many who will find it easier to key off sharper, deep-DOF footage.

• No sharpening/enhancing in camera, keep clean.

This is RED. There is no sharpening or enhancing in camera. It shoots RAW, you add that stuff in post.

• Camera at fast shutter speed (within reason) if actors making large movements.

This ties back to the DOF thing. faster shutter speeds == cleaner and sharper edges and motion, which is often easier to key. So if you want the shallowest DOF possible, are you sure you want to reduce your motion blur as much as you can?

• Shoot at 50-70IRE

I like 65 IRE for my green screen. But it's personal preference. The RED doesn't have an IRE scale, but false color is a good representation and excellent for seeing how evenly lit your screen is.

• 320ASA

The MX sensor (and original M) sensor have a base sensitivity of approximately 320 ASA (same thing as EI 320 or ISO 320). However, when shooting outdoors, it's sometimes handy to set the in-camera ISO setting higher and apply ND as needed in order to protect highlights. The ISO/ASA setting is all metadata anyway and can be dialed in post. MX is typically noise-free up to ISO 800 and even higher. Totally usable up to ISO 2000 in many situations. But if you can shoot with it set as close to 320 ASA as you can, then your on-camera metering will help you more. RAW view and false color are dialed to 320 ASA.

• 5000 Kelvin

It could be, but I guess you'll want to do an auto WB on a proper grey card to check. Anyway, not critical as WB is metadata also and can be fully dialed in post via the RAW controls.

• Keep ISO low to reduce noise 150-200 ideal.

Wait, what? You said 320 ASA above... Actually you want to keep it at 320 and higher on the MX. Dipping lower and you will be crippling your dynamic range. If you must go lower than 320, do so with caution. With the original M sensor, a lot of people liked to shoot tungsten at ISO 200~250 as it helped prevent some of the lack of blue-channel sensitivity and base-level noise. However, on the MX, this is much improved.

• Shoot at 4K for best information.

4KHD or higher all the time. The only reason to shoot lower resolutions on the RED One is for the increased frame rates. And with that comes the compromise of lower resolution and the added hassle of sensor crop, meaning you need wider lenses to maintain similar framing.

• Dynamic range within less than 7stops max.

You have over 13 stops of measured DR on the MX sensor, a good 12 stops usable if you light and expose well. I'm not sure what you're saying here.

LIGHTING
• No more than 0.5stop difference at any point of screen.

Yep. And being outdoors, this shouldn't be a problem if you can keep the screen free of wrinkles or other things that can change the incidence of reflected light. 1/2 stop can still be a big deal, but is OK if the change happens gradually across the screen surface.

• Light greenscreen using daylight bulbs. If Tungsten use 80B/C/D filter.

You're shooting outdoors -- use bounce or daylight bulbs if you need more fill. If for some really screwed up reason you need to use tungsten, gel the lights. If you put a filter on the camera, that just throws your white balance to hell and doesn't actually help you if you have a mix of daylight and tungsten light.

• Green gels could help compensate for faded screen.

Or green tubes. I prefer to light my screen with green tubes if available.

• Back lighting on talent is essential to get separation between actors edges and greenscreen.

Test. Not always needed, but definitely something you will want to prepare for. You're shooting outdoors, there's a lot of factors that can change on you. Sunlight and cloud cover changes constantly.

 

[Tim Whitcomb]

Jeff, you really need to be more specific - don't you think? I would have quoted every word, not every sentence :001_tongue:

 

[Ben Brainerd]

• Shallowest depth of field possible.

Well, Jeff pretty much nailed everything. I just wanted to chime in with my two cents on the DoF point.

If your concern is purely a good key, deeper focus is better. Obviously DoF is a stylistic choice, though.

Using your test shot as an example, if you were handing me the shot to key, I would prefer the actors and the wall be nice and sharp. It's easier to pull a key when the foreground is in focus. When you've got elements in front of the screen that are soft you run the risk of haloing and artifacting in those fuzzy edges. It's obviously solvable, but given the choice a sharper foreground is always better, IMHO.

 

[Matthew Bowyer]

Thanks Jeff, with things like ASA/ISO I had been pulling from too many sources many which didn't refer to MX specifically so having you address everything in regard to MX is such a great help.

Depth of field what I meant is keeping the talent in sharp focus but having the green behind blurred in order to even out the greenscreen if necessary.

Thanks guys, I'd welcome any more tips or anecdotes, as with the schedule here its not looking good for a test day.

 

[Shane Kelly]

I agree with Jeff's post. I use 65 ire on the screen and it always works well. As for using backlight, you don't need it for separation but if it is realistic, then go ahead.
don't go under 320 iso.
I disagree with using a fast shutter. Yes, it will give you a better key but motion will look different.
The screen in your test shot looks overexposed but that could just be the jpeg. Is that digigreen or regular chroma green? Sometimes I find it hard to use the digigreen fabric outside as it barely has to be lit at all. It's great for the studio, though.
It may be better to switch to a regular chroma green for exteriors.
As for your night shot, I would light the screen with the same color of lights that the actors are lit with: daylight or tungsten.

 

[Jeff Kilgroe]

Another note on DOF and shutter speed. Don't stray too far in your shot from the characteristics used for the other footage you're compositing with. You want your motion and blur attributes to match up so it looks like a seamless comp.

 

[richard peterson]

- maybe get a clean plate of each shoot; a few seconds without the talent in frame

- if a shot is moving or has a lot of detail a few seconds of a dark gray card can be used to extract the noise pattern. Add this noise to the comp layers to help it match the live action plate.

- shot still pictures of the lighting setup to help eliminate the guess work for the compositor when matching lighting and scale... if compositing 3D then you may consider shooting HDR spherical panoramic images for accurate reflections and lighting information for rendering.

 

[Ben Brainerd]

- if a shot is moving or has a lot of detail a few seconds of a dark gray card can be used to extract the noise pattern. Add this noise to the comp layers to help it match the live action plate.

This +Eleventy-bajillion. Noise/Grain can make or break a comp. In a setup like the one you've got in your test, it would be easy enough to throw a gray flag/card up next to the screen (In the area you're going to matte out) for a noise sample.

 

[Jeff Kilgroe]

Now we're getting into an FX and cinematography discussion, which is just fine here.... That said, one should always take static plate shots without the talent and shoot black and grey cards for noise / grain matching. That goes for any camera being used. Unless you're shooing with the same camera for everything, then it tends to be easier to match and make it flow. I shoot black and grey cards if the shot will have any motion graphics comp'd in, that way I can duplicate the noise and apply it to the graphical elements as well.

 

[Kim Frank]

Jeff I'm all with you, except for you stating " The RED doesn't have an IRE scale". The Red One has the ability to meter IRE. You can very simply set your Zebras to an desired IRE and it is a great tool to check your greenscreen is exposed right. I even leave it on while shooting, because it doesn't really destract me, wich would be crazy with False color.

 

[Jeff Kilgroe]

Jeff I'm all with you, except for you stating " The RED doesn't have an IRE scale". The Red One has the ability to meter IRE. You can very simply set your Zebras to an desired IRE and it is a great tool to check your greenscreen is exposed right. I even leave it on while shooting, because it doesn't really destract me, wich would be crazy with False color.

You are right, zebras are based on IRE. However, you're shooting RAW, so IRE settings will only apply to whatever look you have applied at the time. Change the ISO, you change the base for IRE measurements. Change exposure, ISO, FLUT, etc.. in post, you change your IRE scale.

You can also judge IRE based on false color and that is actually more accurate, for me in terms of luma % because false color is locked to RAW. It's not truly IRE, but when shooting we care about the exposure and range and not how it will ultimately fit into an IRE scale for broadcast or delivery on some video format. Zebra IRE made perfect sense way back when, when everyone was monitoring and even running through post, in REC709. Now, it's a different story.

Eagerly awaiting an updated camera firmware so we can have RC2/RG2 on-camera as well as REDLOGFILM. I would love to have REDLOGFILM as an available viewing mode in addition to RAW view.

 

[Matthew Bowyer]

Now we're getting into an FX and cinematography discussion, which is just fine here.... That said, one should always take static plate shots without the talent and shoot black and grey cards for noise / grain matching. That goes for any camera being used. Unless you're shooing with the same camera for everything, then it tends to be easier to match and make it flow. I shoot black and grey cards if the shot will have any motion graphics comp'd in, that way I can duplicate the noise and apply it to the graphical elements as well.

Really good suggestion, thank you.

Jeff can I ask where you would put these in the frame? As in full frame grey/black as with a distortion grid, next to actors, or next to greenscreen??

We are also way out on location in Japan right now - are the black/grey cards a specific item or can we DIY it? Is using the camera departments grey card fine for this? What would you use for black?