Filters for greenscreen lighting

[Bert Smyth]

Originally Posted by Ben Syverson

If you wouldn't mind, could you post (or email) a frame from the greenscreen shot, and the background? I'd like to give it a whirl in dvmatte.

I don't have a shot of her out of frame. But here's a screen grab without the Luma Key applied. I intentionally tried to get the background as hot as possible. When I shot, the whole background showed on the zebras as over 100IRE. The only problem with this is that you can see the background is kicking back on her. Let me know how it works with Dv matte.

[Paul Cascio]

Thanks to Ben and everyone who's contributed.

Questions:

1. What suggestions would you give to those of us who can't get the required distance between talent and screen?

2. Is it advantageous to underllight the screen so it's darker than the talent? My thoery is that this will reduce spill. If so by how much?

3. Another theory -- Do you recommend the screen be perpendicular to the floor, or is a slight tilt better to change the angle of reflection?

Thanks

[Bert Smyth]

Paul, if you're in tight quarters, the main thing you have to be aware of is how much the chroma background is kicking back onto the talent. You can compensate for this by trying to ad a backlight to your talent. You don't need to light your background really bright, but you must light evenly. That's the most important element. But understand what Ben is getting at is one and the same. He's talking about using filters so the green coming back to the camera is "pure" which will really help in the keying, but that's in addtion to a very evenly lit background. The idea of good chroma backgrounds is that they don't reflect back a lot of light. Still, if the talent gets too close, you're going to have a problem.

One thing you could try is something like the luma key I did. You can still run into the same problem, but you can use your zebra bars in the viewfinder to see where that might occur. The idea is to light your background so that as you open up your iris, in one step, your entire background goes all zebras. If one section goes zebras, and another doesn't, then your background isn't lit evenly. What I shot for was opening up my iris so the background went zebras in one step, and then reset the zebras for 90 and tried to make sure that the brightest part of my talent wasn't over, reset to 80 and made sure that's what my talents face was at. The luma key worked really well, and it was fairly tight. Before you try all this you'll want to make sure you have a software program that has a Luma Key that can pull out the lighter. I used After Effects.

Ben will probably have some great advice with the Chroma/green screen stuff, as well as post production tips.

[Ben Syverson]

Originally Posted by Paul Cascio

1. What suggestions would you give to those of us who can't get the required distance between talent and screen?

Hi Paul! If you can't get much distance, you'll have to do a good job of flagging your source lights. You want to avoid having those screen lights hit the back of your subject, especially if they're gelled.

More distance will give you less wrap-around spill, but obviously you've gotta work with what you've got! I wouldn't sweat it too much, just make sure your screen and subject lighting is happening on two separate planes. If you turn off your screen lights, you should strive to have a well-lit subject against a VERY dark green BG, and if you turn off your subj lights and turn on the screen lights, you should have a VERY dark silhouette against a nice bright green.

Originally Posted by Paul Cascio

2. Is it advantageous to underllight the screen so it's darker than the talent? My thoery is that this will reduce spill. If so by how much?

Given how easy it is to remove spill, there's no point (IMO) in doing backflips to reduce it. The optimal Green level for the background will vary a little depending on whether you're compositing into a dark or bright scene/background. If the scene is bright, you'll want your Green level at 80-90%. If the scene is dark, the screen can come down as low as 70%. I wouldn't go too much lower. If the background is super dark, maybe 60%.

Color purity is also crucial to the quality of the key -- if you aren't gelling your lights, you wouldn't want your Green level go under 70-80% unless you absolutely had to, because you're already losing fidelity by having an impure screen.

Originally Posted by Paul Cascio

3. Another theory -- Do you recommend the screen be perpendicular to the floor, or is a slight tilt better to change the angle of reflection?

Unless you have a very shiny screen, this shouldn't be too important. Screens are more or less matte, so they're going to reflect in all directions no matter what you do... Especially if you're using soft lights on your screen (which is a good idea).

Bert's idea of using a luma key is also an option. The problem with luma keys is that your matte is only as strong as the difference between the darkest point of the screen and the brightest part of the subject. Sometimes it's so low that you have to squelch the life out of your key. Sometimes it's so low it's a negative number, which means you have holes in your matte. Highlights in the eyes or reflections on buttons will do this every time. In this case, even a terrible greenscreen will give you better separation...

[Bert Smyth]

Originally Posted by Ben Syverson

The problem with luma keys is that your matte is only as strong as the difference between the darkest point of the screen and the brightest part of the subject. In this case, even a terrible greenscreen will give you better separation...

Ben, thanks so much for all your info, this has been a very educational thread. Paul, just to make it clear, while I've done chroma keys where there was lots of room, in this case we were messing around in my garage experimenting with different types of keys, and were able to pull a sucessful Luma key, mainly because we didn't have a good color for a Chroma Key. But even with that, we're actually going to be setting up a green chroma screen, for exactly the reason Ben said. When our talent would smile, her white teeth would get included by the luma key. I totally agree, a Luma key is really "walking a fine line", and I think the better choice for professional shoots is to try and nail down a successful green or blue screen, because you don't want to go into post and realize that the luma key is taking our your talents hand or something.

Ben, thanks again for sharing, that's such good advice about the talent/background light/dark!

[Paul Cascio]

I'm have short, dark hair and an olive complexion. Will I be less prone to spill issues than the good ole' beautiful Susie of the Ultra tutorials?

Does wearing dark clothes help? Anything else?

[Ben Syverson]

Originally Posted by Paul Cascio

I'm have short, dark hair and an olive complexion. Will I be less prone to spill issues than the good ole' beautiful Susie of the Ultra tutorials?

Does wearing dark clothes help? Anything else?

Dark colors will technically reflect less green, only because they reflect less of everything. The percentage of green reflected by a dark gray surface is the same percentage reflected by a light gray surface. But the surface quality of the subject will affect the percentage of light reflected -- in other words, shiny surfaces will show more spill than matte surfaces. So subject brightness won't affect the amount of spill suppression you will need to apply, but surface/finish will.

That said, I have to reiterate that people make too big a deal about spill. Modern software is extremely good at removing spill. Reflections are far more problematic than spill. So if your subject is sweaty, shiny, etc, you may have some issues. But a little green spill is a non-issue.

I've attached an example. It's a quick and dirty test shot I did in my apartment. The background is green posterboard from CVS lit with daylight. I'm literally right up against the screen, and the screen is very bright.

The first image is the raw capture (note: all of these were resized from a random 804 x 603 image I had on-hand, so they don't represent the HV20's image quality, which is much, much better)

The second image is a neutral-ish spill removal. Notice how completely the green has been corrected out. This is not a composite -- just a spill correction.

The third image shows that I can correct to any arbitrary color -- here, orange. This would help if you were compositing against a bright orange graphic like Bert was with his luma key example.

The fourth image shows that we can get all the way to blue.

The fifth image shows that we don't have to limit ourselves to correcting to a single color -- here, I'm correcting the green to the color of the background, on a per-pixel level. Again, this is not a full composite, just a spill removal. If we were to use a nice matte to composite this against the background, we'd be getting somewhere.

[Ryan Avery]

Originally Posted by Ben Syverson

Hi Ryan!

Yeah, I should be extra-clear in case there's any confusion. I'm suggesting Lee 738 as a lighting filter for the screen only, not as an on-camera filter... On the camera, unfiltered is definitely best -- unless you aren't able to get your in-camera sharpening low enough, in which case it might make sense to test a 1/4 or 1/2 Black Pro Mist or similar.

My experience with magenta backlighting hasn't been very promising -- I wind up having to struggle to remove the magenta cast in my edges. Can you elaborate about that technique a little bit, or even better, post an example frame?

Kino does make green bulbs... Hmm, maybe a Composite Components Digital Green vs Kino green shootout is in order. :)

Magenta backlighting should only be used if you are experiencing a great amount of green artifacts or fringing or what ever green screen experts (not me) are calling it. Either way, I have used the lightest possible magenta from LEE and it fixed the problem.

I can't imagine using a camera filter for this application that would be shameless promotion of my product (which is not above me). We do make cc Green filters but obviously wrong application.

The Kino bulbs work very well. I prefer them to other solutions if nothing else for the ease of use. 1/2 hiegth of the screen back from the screen on a ceiling track and shooting down at a 45 degree angle with a white screen and I was able to get excellent results using the Kino green bulbs on a couple of Diva lights.

[Ben Syverson]

Awesome! Thanks for sharing, Ryan!

[Les Caudle]

Ben - I just ordered the 738 JAS Green filters - can't wait to try them out.

I notice that you use a MacBeth ColorChecker.

I shot a subject against my green screen last night, and the color of her sweater was different going out from FCP thru HDMI to a Samsung 245T.

So, I'm definitely going to have to calibrate the monitor (and possibly the HV20 with my fluorescents).

Unfortunately, I can't use my Gretag MacBeth Eye One Display - as the output to the HDMI is only thru FCP (no way for it to detect where on the screen it is).

One suggestion was to shoot the ColorChecker with my HV20, and adjust the monitor's picture to match it.

Other folks on the FCP forum said that would create problems.

I thought I might rip a calibration DVD and play that thru FCP to the HDMI.

Any ideas? Trying not to spring for an MXO (that has calibration) right now - and am trying to talk Black Magic into adding some calibration tools to their Intensity card.

Thanks!

[Ben Syverson]

Les, can you use the monitor as a second display through HDMI? (ie, can you throw a Finder window onto it?) If you can, you can use SuperCal ( http://www.bergdesign.com/supercal/ ) to calibrate the monitor manually. It won't be as perfect a calibration as you can get with the Eye One, but at least it will be calibrated.

I only use the Color Checker to check white balance, and as a sanity check on exposure. I wouldn't try to profile or calibrate anything based on it -- there are just too few swatches to sample from to build up a whole profile...

[Jim Ross]

Ben,

Applications like Ultra2 (which I use and love) assert that the background color is not so important. Your illustration of the importance of the color has me thinking very differently. From your tests I would venture that the chroma screen itself will have a lot to do with the results? After all, all chroma screens are not created equal. Being in the biz of writing this kind of software, do you find this to be true? That you get what you pay for and cheap green/blue screens give you lesser results?

I currently use a blue backdrop that matches chroma blue and get really good results because I light the thing perfectly. It is not a real blue screen, just a fabric that, to my eye, exactly matches. I wonder if I used a real one I would not get "good" results but "great" results?

Jim

[Nick Jushchyshyn]

Not to speak for Ben, but figured I'd chime in with my own opinion....

The exact shade really doesn't matter too much for "pulling a key". You can do it, even with wrinkles and shadows. What I've seen of Ultra looks really really good, but mostly (just my opinion) mainly for glossy corporate video/tv ad keying where you're shooting a person with a stationary camera as they talk about whatever it is they need to talk about for the video.

Nothing wrong with that. Great, very productive, lightning fast, and great looking quality with virtually nominal expense. Optimizing screen color is big-time overkill for this type of content.

There's a level of compositing that strives to go quite a bit further that though.
Where extracting as much detail from frizzy hair and semi transparent objects and cloth as possible, without any hint of chatter, and combining it with a touch of subtle light from the new background wrapping the edges of the subject, and bright lights from the new background glow around greenscreened objects that pass in front of them.

At this level, ever little bit of optimization on set can directly improve the detail and quality in the final comp.

Now ... in big budget films, you pretty much never get this kind of optimization. Heck, these days you're even lucky to have a bluescreen or greenscreen at all. Issues of poorly lit, non optimized screens with wrinkles and seams (or no screen at all) are addressed by armies of effects artists that will literally trace a matte around people and objects ... frame by frame for pretty much the whole film. (if you're unfamiliar with this, have a look at this behind-the-scenes video from Peter Jackson's Kong production diary that covers the subject: http://www.kongisking.net/perl/newsview/15/1125073579)

Of course, independent producers and directors really don't have the kind of budgets to be able to pay for such an effort ... so this is where optimization of the screen (down to color) can really pay off in helping produce a very high-end finished look, with much less effort and work than gets put into multi-million-dollar movies.

Hope this helps.
Have fun.

[Nate Benson]

after watching that short on Jackson's King Kong rotoscope artists, I'm amazed that a production that big wouldn't just get the shot right. I feel like more money is used up to spend in post-production when they could have just taken more time to get the shot right.

But then again, I'm a student filmmaker so I come from a world where I have $500 to make a short film and I have to go do it.

[Nick Jushchyshyn]

Originally Posted by Nate Benson

after watching that short on Jackson's King Kong rotoscope artists, I'm amazed that a production that big wouldn't just get the shot right. I feel like more money is used up to spend in post-production when they could have just taken more time to get the shot right.

But then again, I'm a student filmmaker so I come from a world where I have $500 to make a short film and I have to go do it.

Actually, it's "on set time" that's the most expensive.
On set costs include rental of the facility, the equipment, the director's pay plus that of all the assistant directors, producers, script supervisor(s), camera crew (per camera), high-paid talent, low paid talent, an army of people that move everything around, not to mention that film costs (including transport and scanning) is not cheap.

In the end, the cost of a roto artist's time to roto out that stuff in the background is nominal compared to setting up and rolling again to retake a shot .... not to mention that the director could have REALLY liked the actor's performance on a given take and you never know how many re-takes would be needed to get that particular performance again.

The roto work on Kong isn't even the heaviest I've seen. Consider the canibal island shots with all the natives with spears and detailed head-dresses and various ferns and rope bridges and such .... ALL of which had to be roto'ed since the director decided to change the look of the background after having shot with NO bluescreen.

Another heavy roto example is Flags of our Fathers/Letters from Iwo Jima, where Eastwood didn't want bluescreen on location since it would slow down and distract his production process. All the live action soldiers(and their gear) on the beach had to be traced so that the background could be added in without keying. Go to the Digital Doman website, click Features, Click "Behind The Scenes" and click the fifth panel on the top row (Flags of Our Fathers) to see some of the shot buildups.
Consider that when the soldiers are waving at the plane fly-by ... all those heads, arms, hats, and cables were traced so the whole background could be replaced ..... and that's just one of the hundreds of shots on the show.

Have fun.