Shooting bluescreen on RED-One MX

[Brandon Kraemer]

I've done some research on reduser on this topic, but I am finding mostly older posts (listed below) that are pre-MX sensor. I could use some feedback about this topic please.

An upcoming shoot will be likely using the RED-One MX... shooting bluescreen on a sound stage. DP is proposing lighting the bluescreen cyc with HMI lighting, possibly skinned in 1/4 CTB, and lighting the foreground with Tungsten. Greenscreen is NOT an option unfortunately, Epic is not available to us. Having read the posts below and based on past experiences pre-MX, we think that with enough watts this will give us clean keys, we are most concerned about edges.

Q: Does the newer MX sensor eleviate any bluescreen issues beyond stops of light?

Q: Is the idea of mixing HMI/Tungsten advisable in this situation? Is camera filtration a useful tool here?

Director is concerned and has mentioned other camera options: F35 is out of question for budget, Alexa has been mentioned by the director as well but we wouldn't have the ability to capture RAW or push into shots. Scientifically speaking if my facts are straight the RED M sensor has 200% more Green pixels vs. Red/Blue.

Q: Does the Alexa have more pixels of Blue than the RED MX?

Thanks for helpful replies.

bk

http://reduser.net/forum/showthread.php?15924-Green-Or-Blue-Screen&highlight=bluescreen

http://reduser.net/forum/showthread.php?15385-Bluescreen-with-Tungsten-Lighting&highlight=bluescreen

http://reduser.net/forum/showthread.php?5705-RED-and-bluescreen-or-greenscreen&highlight=bluescreen

 

[Jake Bastian]

RED is awesome for keying so you're good there but there are a few concerns. Mixing HMI and Tungsten is only advisable if that's the look you're going for. If I'm going for "white" light, I'll use daylight bulbs on the subject - changing the temperature of the lights with gels and such rather than changing metadata on the camera to get a different color of white. I know you can change color temp on camera, but I like shooting closer to what the sensor is balanced for because changing the metadata always introduces noise which translates to a more difficult key. Again, this all depends on the look you're shooting for. 1/4 CTB on the lights for the background is a great idea to boost the blue in the screen - when shooting greenscreen I go with green bulbs when i need a fast/good key in post. I would stay away from camera filtration as you lose stops of light. See next:

As far as edges go, the best way to get a clean key around the edges is to shoot with as much DOF as possible (i.e. not wide open) as any blur around the edges will make a clean key more difficult to pull. Not impossible, it just takes a lot more finesse. Actual f-stops will depend on focal length, distance etc but try to keep enough DOF to focus on the entire subject. If you have multiple focal planes in shot, and have time, you should shoot them separately (all in focus) and then change DOF during the composite to achieve your desired look.

Can't comment on Alexa but IMO more pixels is better meaning RED will probably come out better in the case of pulling keys. Hope this helps.

 

[Eki Halkka]

Q: Does the newer MX sensor eleviate any bluescreen issues beyond stops of light?

Much less noise = cleaner key.

Q: Is the idea of mixing HMI/Tungsten advisable in this situation? Is camera filtration a useful tool here?

Theoretically using HMI for the bluescreen, and tungsten to light the foreground subjects should work rather nicely: when balancing the shot for tungsten in post (or better yet, using a daylight conversion filter on camera), you get supersaturated blue for the backdrop, with properly colored foreground. This worked rather well back in the day with DigiBeta i recall - as long as the backdrop and subject had enough separation to avoid spill (i wouldn't advise this approach if the subject i.e. has to stand on the bluescreen floor).

I haven't shot blue in a long time though, and never used this method with Red MX, so take this all with a grain of salt.

Q: Does the Alexa have more pixels of Blue than the RED MX?

As far as i know, no. Both use similar Bayer pattern CMOS sensors, but Red has more native resolution.

 

[sergio arguello]

No disrespect to your Dp as everyone has a way they prefer to do things. I would light it as i would film. I do understand good an well that the sensors these days have a need for Blue. But 2 things
spacelights are the easiest way to get an even green (blue) screen and they can be adjusted from the floor...HUGE 2. tugsten is cheap bang for the buck.and if you dont want to starve the sensor of blue correst in front of the lens 3. RC42 a must!!! and the best glass your Dp can get his hands on...crucial. Chromatic abberation is a beeline to roto. IMHO

 

[Jake Bastian]

No disrespect to your Dp as everyone has a way they prefer to do things. I would light it as i would film. I do understand good an well that the sensors these days have a need for Blue. But 2 things
spacelights are the easiest way to get an even green (blue) screen and they can be adjusted from the floor...HUGE 2. tugsten is cheap bang for the buck.and if you dont want to starve the sensor of blue correst in front of the lens 3. RC42 a must!!! and the best glass your Dp can get his hands on...crucial. Chromatic abberation is a beeline to roto. IMHO

If you're going with tungsten bulbs on the blue that's fine, but gel is cheap so you should balance it to daylight to keep away from sensor noise that will show up when you're shooting tungsten on a daylight sensor RC42 or not - the same thing would happen with daylight balanced film so it's not a matter of shooting the same as you would for film.

Doesn't matter how sharp/distortion free your lenses are, if your DOF is off you're going to have soft edges so keep your light levels higher than you would normally.

 

[Gavin Greenwalt]

Even with MX I would recommend going daylight if it's possible. The blue on RED is still pretty noisy under Tungsten. You'll still be able to pull a key fine it'll just be that much more tricky. Oh and agreed on shooting as high of bitrate as possible if you're shooting blue.

 

[Alexander Ibrahim]

Red MX is much better than Red One M for bluescreen because there is a lot less noise, particularly in the blue channel.

There are always issues mixing tungsten and HMI, but if your DP and gaffer are on the ball, then it will be fine.

Yes Red MX has way more blue pixels than Alexa.

I have to think that anyone asking has an Arri oriented agenda. Red One is "4.5k" It resolves to more than 3x as many pixels as Alexa in every color channel.

F35 is an insane step backwards from using Red for chromakey ... even in its uncompressed modes. Its really just a dolled up 1080p video camera ... so I'd definitely pick Alexa over F35, and Red One MX over Alexa.

I can also add that I've shot a LOT of chromakeys with Red One M (Blue, Green and Orange!) and it performs VERY well. I'd pick it over F35 and Alexa as well, with the caveat that your DP must be prepared to deliver the light the camera needs or take some other steps on set. Its never been a problem for me, but some DP's just can't or won't modify their standard approach.

I do think that F65 will be a better choice for bluescreen than R1MX, but probably not notably better than Epic.

 

[Brandon Kraemer]

Thank you.

Thank you.

Terrific information, thank you all.

 

[sergio arguello]

If you're going with tungsten bulbs on the blue that's fine, but gel is cheap so you should balance it to daylight to keep away from sensor noise that will show up when you're shooting tungsten on a daylight sensor RC42 or not - the same thing would happen with daylight balanced film so it's not a matter of shooting the same as you would for film.

Doesn't matter how sharp/distortion free your lenses are, if your DOF is off you're going to have soft edges so keep your light levels higher than you would normally.

hence my coment to correct on the lens...gelling skypan???? never seen it don well...blazing hot lamp

sorry didnt quite get your Depth of field comment...as thats a stop choice and this is a color temp discussion please enlighten me

 

[Alexander Ibrahim]

If you're going with tungsten bulbs on the blue that's fine, but gel is cheap so you should balance it to daylight to keep away from sensor noise that will show up when you're shooting tungsten on a daylight sensor RC42 or not - the same thing would happen with daylight balanced film so it's not a matter of shooting the same as you would for film.

Doesn't matter how sharp/distortion free your lenses are, if your DOF is off you're going to have soft edges so keep your light levels higher than you would normally.

You don't have to have daylight balanced light on the bluescreen! What you need is a lot of light. The bounce from the bluescreen is already a blue light source to the camera, just keep it bright. I like to keep it reflecting a t/11 or higher, moderated by the need to keep spill under control. (and of course I don't want it to blow out ... but that shouldn't be an issue at just t/11 reflection)

Let me put that differently ... you want to make sure that if nothing else you can pull a luma key off the screen.

Now, if you are shooting a screen color other than blue, then you need to make sure your light source had good blue levels in it. Any high CRI light will do the job if you pour enough light in, but even fairly low CRI daylight sources will work well. I once used a chicken coop with tons of 23watt CFL 5600K bulbs from Lowe's. Remember ... you don't care about "accurate color rendition" on the screen, just uniform color and brightness. You just want it to key!

I agree that you generally want to keep your stop up. The goal is enough DoF to keep every edge you want to key sharp. Conversely you want a shallow enough to DoF to make certain that the bluescreen is nicely blurred out. If you can use a bigger screen and keep it further from the camera and subjects, then you can use a fairly deep stop if you like.

 

[Jake Bastian]

hence my coment to correct on the lens...gelling skypan???? never seen it don well...blazing hot lamp

sorry didnt quite get your Depth of field comment...as thats a stop choice and this is a color temp discussion please enlighten me

This is a shooting blue screen for keying discussion DOF comment was about maintaining edge fidelity and correcting the lens cuts out stops of light - less stops of light - wider aperture - less DOF - subjects edges can go fuzzy which makes it harder to pull a clean key. Not saying it can't be done, just saying it's less than ideal.
Also, shooter is wanting to light the subject with Tungsten and the screen with Daylight correcting the lens won't allow him to do that. Sorry I glossed over the skypan comment, but I stand by my original statement that lighting with Tungsten is a mistake if you're shooting Bluescreen.

You don't have to have daylight balanced light on the bluescreen! What you need is a lot of light. The bounce from the bluescreen is already a blue light source to the camera, just keep it bright. I like to keep it reflecting a t/11 or higher, moderated by the need to keep spill under control. (and of course I don't want it to blow out ... but that shouldn't be an issue at just t/11 reflection)

Let me put that differently ... you want to make sure that if nothing else you can pull a luma key off the screen.

Now, if you are shooting a screen color other than blue, then you need to make sure your light source had good blue levels in it. Any high CRI light will do the job if you pour enough light in, but even fairly low CRI daylight sources will work well. I once used a chicken coop with tons of 23watt CFL 5600K bulbs from Lowe's. Remember ... you don't care about "accurate color rendition" on the screen, just uniform color and brightness. You just want it to key!

I agree that you generally want to keep your stop up. The goal is enough DoF to keep every edge you want to key sharp. Conversely you want a shallow enough to DoF to make certain that the bluescreen is nicely blurred out. If you can use a bigger screen and keep it further from the camera and subjects, then you can use a fairly deep stop if you like.

Yes, tungsten light will hit the bluescreen and bounce back more blue than it was before, but it will also bounce back much warmer than if you had just hit it with a blue (daylight) balanced light to begin with. Sure you can use a tungsten light, but why would you if you had the choice? Especially when shooting a daylight balanced sensor.

I would also never plan to - "if nothing else make sure you can pull a luma key" - if you plan to shoot on chroma blue then you should be planning to pull a chroma key. Why plan for failure?

 

[Alexander Ibrahim]

Yes, tungsten light will hit the bluescreen and bounce back more blue than it was before, but it will also bounce back much warmer than if you had just hit it with a blue (daylight) balanced light to begin with. Sure you can use a tungsten light, but why would you if you had the choice? Especially when shooting a daylight balanced sensor.

Well, budget for one. Also ... there are plenty of facilities with tungsten installed. You might have a ton of practicals you can't mess with that are tungsten ... be imaginative.

I would also never plan to - "if nothing else make sure you can pull a luma key" - if you plan to shoot on chroma blue then you should be planning to pull a chroma key. Why plan for failure?

What I mean is that if your screen isn't bright enough when metered reflectively, i.e. using a spot meter, to pull a luma key from it will probably also fail as a chromakey.

So, as to why you would plan for failure ... well because sometimes things fail.

I once had a shoot where VFX had brought out some specially prepared orange plates to be used for chroma key, to be replaced with computer displays.

To their surprise, because they didn't consult with me, the set was lit primarily in red. Even if I threw white light on that a chroma key would be hairy at best.

So, they flipped the cards over to where they had a green screen painted. A few white light specials and hasty tracking markers later, a ruined day was a working day.

On another shoot we had a pile of Klingons kicking around and ... you guessed it: a set lit in red! (Why I get stuck with red sets ...) VFX had orange cards. So the word "rotoscope" got all over their day ... in a mass fight scene. I bet they wish they had a backup plan.

The moral of the story, if you think your plans will never fail, then you too will screw up a shoot. So, have a backup plan. I believe its called "hubris."

Better yet, a back up plan that can be executed with no extra time/expense than the primary plan.

You know, like lighting your chroma key screen bright enough so you could also pull a luma key.

 

[Eki Halkka]

Let me put that differently ... you want to make sure that if nothing else you can pull a luma key off the screen.

I have to say that as someone who composites this stuff pretty much every day, i strongly oppose this idea. The backdrop should be lit EVENLY, and to the same exposure as the foreground (around 50% luminosity). The more SATURATION you have in the BG, the easier it is to pull the key (assuming proper isolation between BG and FG). Overlit blue/greenscreen is a nightmare to key.

 

[Brandon Kraemer]

Yes Red MX has way more blue pixels than Alexa.

I have to think that anyone asking has an Arri oriented agenda. Red One is "4.5k" It resolves to more than 3x as many pixels as Alexa in every color channel.

I don't think there was an agenda behind that question, just a lack of information. To rephrase it...

Q: Is the ratio of red/blue to green pixels the same on RED and Alexa given that they are both CMOS sensors?

 

[Jake Bastian]

I have to say that as someone who composites this stuff pretty much every day, i strongly oppose this idea. The backdrop should be lit EVENLY, and to the same exposure as the foreground (around 50% luminosity). The more SATURATION you have in the BG, the easier it is to pull the key (assuming proper isolation between BG and FG). Overlit blue/greenscreen is a nightmare to key.

This is what I'm saying. A bright screen corrupts your edge detail even worse than shallow depth of field. The point of planning is to avoid things like red/orange light on orange cards. it's not hubris is common sense and it doesn't compromise my ability to adapt to a shitty situation.

 

[radhika mallick]

HI EVERYONE,

I HAVE A BUNCH ( I MEAN ALOT) OF BLUE SCREEN AND GREEN SCREEN FOAMBACKED MATERIAL. IF ANYONE IS INTERESTED - I GOT A GREAT DEAL AND AM WILLING TO PASS ALONG THE GREAT DEAL. IT IS NOT MUSLIN. TOTALLY WRINKLE FREE STUDIO STANDARD. I AM IN LOS ANGELES (818) 232-2967 RADIKA OR SEND ME A MESSAGE HERE

THANKS

 

[Alexander Ibrahim]

I have to say that as someone who composites this stuff pretty much every day, i strongly oppose this idea. The backdrop should be lit EVENLY, and to the same exposure as the foreground (around 50% luminosity). The more SATURATION you have in the BG, the easier it is to pull the key (assuming proper isolation between BG and FG). Overlit blue/greenscreen is a nightmare to key.

Well, if you want to compare credentials, that's fine ... but I think reasoning should win out over credentials every time. If you insist however, then look me up.

I agree that a bluescreen should be lit evenly ... I don't see where I mentioned otherwise. You don't think that bright lighting requires uneven lighting do you?

Overlit?

Obviously you don't want the screen to clip, I didn't suggest that at all. Pardon me for assuming the audience would know better. Maybe you don't so let me lay it out:

My suggestion was a reflection of t/11 or higher. Most shoots have a stop in the t/4 - t/5.6 range. That means I'm suggesting 2-3 stops over key, which is well within the range of Red MX which easily gives 5 stops over/under latitude. (10+ stops DR)

That puts you at least 2 stops under clipping, (more because Red MX's DR is more than 10 stops!) and gives a deeply saturated color - you did want saturation right?

So what's left? You suggest the luminosity match foreground subjects very closely.

In fairness, you should add color to the lighting as your screen gets brighter relative to the subjects, and definitely within the last stop of your camera's latitude. For Red shoots I tend to add chroma colored gels (or use chroma colored lighting) when I am 5 stops over key with the screen. That rarely happens though without a specific reason.

I usually aim 2-3 stops over key ... t/11 is my target. Now ... if I've selected a t/2.8 as my key, I'll aim for t/8 on the screen. If I have a lesser camera (say a 7D) I'll drop to 1-2 stops over key.

I have been playing fast and loose with the figures because I expect that your DP will want to figure it out for themselves. If you want it lit the way I'd light it, then you should hire me to direct your photography, right?

So ... as DP I spend time imagining ways production can screw a shoot. Here is a simple question. You let the AD know you are lit and ready to shoot your blue screen. What happens when the talent shows with their hair dyed blue? (Or perhaps the aliens show up with their skin matching your screen!)

On my shoot VFX can pull a luma key, while on your shoot VFX will no doubt enjoy the roto work.

 

[Alexander Ibrahim]

This is what I'm saying. A bright screen corrupts your edge detail even worse than shallow depth of field. The point of planning is to avoid things like red/orange light on orange cards. it's not hubris is common sense and it doesn't compromise my ability to adapt to a shitty situation.

False.

I can understand your confusion though.

A bright screen can increase spill, and increased spill can corrupt edge detail. The cause of the bad edge details is spill, not brightness.

The answer isn't to dim the screen, but to control the spill. I unfortunately assumed you all understood this cause/effect and knew how to control spill.

You either increase backlight level, or you must increase physical separation between the subject and the screen.

As to planning, I agree that planning is best. As to my calling it hubris ... if you think planning will solve everything at all times, that is hubris.

You think its simple, and you are right. You will still screw it up, just get comfortable with that. You won't screw it up because you're an idiot, or lazy or unprepared or in any way a bad film maker. You just won't get the memo - or someone else will make a change and no one will communicate it to you.

The old maxim "hope for the best, but prepare for the worst" applies. If you think it doesn't apply to you, that is the point of hubris.

So, you've gotten the memo, planned out your blue screen and lit carefully. When a blue skinned alien shows up on set ... what is your plan? Go complain to the producer? Or shoot because you have a plan for that sort of screw up?

I don't know about you, but producers hire me because I shoot. They don't seem to like it when I complain, no matter how reasonable the complaint.

 

[Eki Halkka]

Well, if you want to compare credentials, that's fine ... but I think reasoning should win out over credentials every time. If you insist however, then look me up.

Sorry, i didn't mean to try to pull rank or anything... rather just to point out that i base my opinion on personal experience in post production - that i'm often the guy pulling the key... or rotoscoping ;-)

I agree that a bluescreen should be lit evenly ... I don't see where I mentioned otherwise. You don't think that bright lighting requires uneven lighting do you?

No, i just meant that there should be enough light to illuminate the screen evenly - in other words, that using neutral levels doesn't mean neglecting the lighting.

Overlit?

If the foreground is more or less optimally exposed (highlights within stop or so from clipping), i'd assume lighting a green/bluescreen bright enough to luma key would mean either clipping the channel for the key color, or underexposing the foreground subject.

I've gotten badly clipped footage a few times, from DP:s that have heard from somewhere that "greenscreen needs a lot of light"... so i'm a bit allergic to that advice. Not a big issue with Red i guess, as there's plenty of dynamic range to go around, but the advice might result in unusable footage, especially with lesser cameras.

That puts you at least 2 stops under clipping, (more because Red MX's DR is more than 10 stops!) and gives a deeply saturated color - you did want saturation right?

Yep, saturation is good. But usually when lighting bright, there's a lot of contamination in the backdrop color, as the color of the backdrops is not really pure (if you use greenscreen, there will be rather high blue and red levels for example). That's not necessarily desirable. Also, there will be unnecessarily high levels of spill from the backdrop color to the foreground, and anything that's even slightly reflective will be heavily contaminated.

So what's left? You suggest the luminosity match foreground subjects very closely.

No, i suggest to light the backdrop to even 50-60% illumination. The foreground can of course be brighter or darker than that, depending on the desired mood. But if you light the foreground subject with the same light levels, you usually get a pretty decent "normal" exposure.

In fairness, you should add color to the lighting as your screen gets brighter relative to the subjects, and definitely within the last stop of your camera's latitude. For Red shoots I tend to add chroma colored gels (or use chroma colored lighting) when I am 5 stops over key with the screen. That rarely happens though without a specific reason.

Using gels doesn't hurt at lower levels either - it helps to get a more pure color usually.

So ... as DP I spend time imagining ways production can screw a shoot. Here is a simple question. You let the AD know you are lit and ready to shoot your blue screen. What happens when the talent shows with their hair dyed blue? (Or perhaps the aliens show up with their skin matching your screen!)

On my shoot VFX can pull a luma key, while on your shoot VFX will no doubt enjoy the roto work.

Oh well... if my talent has a blue hair, i shoot greenscreen, not blue. Duh. In the unlikely case i want to pull a luma key, i shoot white or black screen... but yeah, i get your point - a backup plan is always a good idea. I guess pulling a luma key from greenscreen can work as such, but i'm still not yet at all convinced that it would be a good practice to use in normal situations.

How about the more common situation: your talent stands on the greenscreen... how do you pull a luma key then?

;-)

 

[Alexander Ibrahim]

Sorry, i didn't mean to try to pull rank or anything... rather just to point out that i base my opinion on personal experience.

Pull rank? lol "My show's bigger than yours" ha. It is rather silly, made me smile when you wrote it that way.

No, i just meant that there should be enough light to illuminate the screen evenly - in other words, that using neutral levels doesn't mean neglecting the lighting.

I really think we agree perfectly here, so no point going on about it. Light your screens as evenly as possible at all times.

I'll take it further though, if you have to choose between my idea of lighting the screen brightly and even lighting - always choose even lighting.

In order to pull a luma key, your greenscreen should be brighter than your foreground subject, right? What if you have someone with a white shirt as your subject (not a rare occasion)?

Well now you see some of the reason in my madness. That white shirt should be brighter than the screen ... so you can luma key it, and subtract that from the luma key of the chroma screen.

Or use some other combination of chroma and luma keys to build up a working matte.

Yep, saturation is good. But usually when lighting bright, there's a lot of contamination in the backdrop color, as the color of the backdrops is not really pure (if you use greenscreen, there will be rather high blue and red levels for example). That's not necessarily desirable. Also, there will be unnecessary high levels of spill from the backdrop color to the foreground.

Using gels doesn't hurt at lower levels either - it helps to get a more pure color usually.

I agree, and the brighter you aim for the screen to be, then the more you want your screen to be lit with just the intended chroma key color.

At the ranges I am talking about though ... it does matter, but not enough in a practical sense.

No, i suggest to light the backdrop to even 50-60% illumination. The foreground can of course be brighter or darker than that, depending on the desired mood. But if you light the foreground subject with the same light levels, you usually get a pretty decent "normal" exposure.

On my shoot VFX can pull a luma key, while on your shoot VFX will no doubt enjoy the roto work.

Oh well... if my talent has a blue hair, i shoot greenscreen, not blue. Duh. In the unlikely case i want to pull a luma key, i shoot white or black screen.

Well ... I think you missed my point. The talent has colored their hair unbeknownst to you. "Talent" can sometimes be mildly insane from my perspective

I've had that exactly that surprise happen. I was hired for a music video. We did our prep, and our pretty brunette singer agreed to everything. We get a green screen studio, arrive early, prep, stage and light. Then she shows up, right at her call time, with green hair.

What could I do? We were in a studio with walls painted green .... we had no other screen materials on set. At the very least, we would have had to acquire some bluescreen or other choma screen material. We might have had to do a company move. It could easily have cost the day.

So (and this is when I invented this idea) since I had the lighting power, I turned up my lighting 2 stops and pulled a luma key on set as a test. It worked splendidly.

Now its a part of my standard practice.

Its a backup plan though, not the primary plan. I mean ... if I really wanted a luma key, like you said I'd shoot against black or white background.

How about the more common situation: your talent stands on the greenscreen... how do you pull a luma key then?

You mean how do I eliminate the shadows in the key?

I don't. I try to pick ranges which key just the shadows, color correct them as a separate layer and put them back on the background. When that doesn't quite work (as happens most often) I can use it as a guide for generating shadows in 3D, then I add them to the shadow key, and add that mess back in to the plate.