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August 2014
Issue: July 1, 2009

GREENSCREEN TIPS

By: Randi Altman
Whether you are directing, supervising or compositing a greenscreen shoot, you know that certain rules need to be followed to keep the post pain to minimum. The garbage in, garbage out adage applies.

Some of these rules are obvious or at least should be to pros, but other less-known lessons come from years of hands-on experience. Here, some very gracious professionals share tips they have picked up along the way. We hope these help you next time you are putting an actor, or item, in front of a screen of any color.


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RUSHES HELPS LESBIAN VAMPIRE KILLERS


London's Rushes (www.rushes.co.uk) uses greenscreen on just about all of its projects, so they know all too well the good, bad and ugly of working this way. Recently they finished a film called Lesbian Vampire Killers, where they provided about 160 greenscreen shots, including 2.5 minutes of the film's prologue. But we'll get to that in a bit, first let's focus on Jonathan Privett's top tips for working with shots to be keyed. He's Rushes' head of 3D.
TIP: Get the maximum separation possible between the subject and your greenscreen. "If your subject is too close to the screen you get a lot of green light spill back on to your subject, which is going to cause you trouble when you are keying the edges. You also get green interference on the edge of the individual as well. The further away the screen is, the larger it needs to be if you are shooting an object or subject."
TIP: Light your screen evenly. "Use Kino-Flo lights if you can find them; they provide a very even light and intensity. When you are keying a greenscreen, if the screen itself varies in the intensity of exposure that will cause problems when you are trying to key it because obviously your keyer is looking for a particular color of green, and if your intensity is varying across your screen that is going to cause you more issues."
TIP: Use fabric greenscreens. "People do paint things in chroma key green, but fabric is much better; you don't have any problems with reflections and joints and things when you are using fabric."
TIP: If you want a person to appear to be outside, then shoot the greenscreen outside. "Generally speaking, it's very, very hard to make something shot interior greenscreen with a subject look like that person is outside. The sun is so intense and you get so much bounced light from everything around you; it's really hard to simulate that inside properly, even with lots of expensive space lights.
"If your background is overcast and you are shooting your greenscreen on a sunny day you'll have to put a couple of silks up so the subject is shaded, but you should still do it outside. As far as pulling the key, shooting outside poses its own problems. You may still need to light the greenscreen if there is not enough light or if you can't turn the screen in the direction of where you want to get the sun. Remember, to make the subject look correct compared to your background, you need to shoot the background before your greenscreen."
TIP: If trying to put footage into a television, don't put green things over or inside it. "You need the reflections in the room. If you just have the television switched off, you get all the nice reflections in the room and are normally able to track something off the television. An exception would be if someone with frizzy hair had their head in front of it — then you would need a greenscreen!"
TIP: If you are shooting a subject that will end up being out of focus in the scene, do not shoot them out of focus. "Shoot them in focus and then de-focus them later in the composite when doing the computer graphics work because pulling keys of defocused subjects is problematic."
Rushes put many of these tips to use for the indie film Lesbian Vampire Killers, which only had a budget of roughly three million pounds. The film opens with a prologue that takes viewers back to medieval times in order to explain why girls in a small village in England turn into vampires at 18— very good question!
"They wanted to go stylistic for that, which was completely different from the rest of the film," Privett explains. "It was decided that the backgrounds would be digitally painted, but the foreground people would be shot live action."
There is a knight who takes on a vampire queen, and the action is set in different locations. Rushes shot all 2.5 minutes of the greenscreen footage in one day.
Privett also says there was quite a lot of contact with the ground because you see the characters' feet. "This is always tricky because you then have to light the floor and the back of the greenscreen. And they wrinkle the greenscreen when they move, so you have to pull the shadows off — which was quite a lot of work."
Lesbian Vampire Killers was shot on the Red One camera with an early version of the Red's software, so they encountered blue channel noise from the camera — but found workarounds. Privett says, ideally, he likes shooting greenscreen on reasonably slow 35mm stock, but he did enjoy working with the Arri D20 (now available as the D21) while working on Guy Ritchie's RocknRolla. In terms of post gear, Rushes uses Apple Shake for compositing and Primatte and The Foundry's Keylight for the keying. All told, of the 250 VFX shots on the film — all completed by Rushes — 150 to 180 are greenscreen.

NEW DEAL LIFTS AMELIA EARHART OFF THE GROUND

Matthew Gratzner is VFX supervisor at Los Angeles-based New Deal Studios (www.newdealstudios. com); he spends a lot of his time working on greenscreen shoots. Years of experience and new tools have made this process much easier. Here, he shares some of his experiences.
TIP: Make sure your screen is minimally 15 to 16 feet away from your subject. "You don't want lighting spill from the composite screen, which can be a problem. There is no excuse for bad compositing or spill because there are so many tools now that can reduce spill, however why make it more work in the end. If there is a little spill, it can also be color corrected out in the DI process."
TIP: Ideally, light your screen as evenly as possible, but you still have some options. "With the compositing and matte pulling tools now — we use Nuke and Shake for a lot of our composite work — you can average the background and just about pull the mattes from anything. It's not like the days of optical printing using a chemical process, where you need a perfectly pure, perfectly lit, balanced screen. It certainly makes your job much easier, but it's not as instrumental as it was in the past. You can get away with a lot more now."
TIP: You get sharper mattes with greenscreens. "We shoot with any composite screen — it could be blue or green etc. — but the green channel is easier to pull mattes on, particularly with the Red camera and a lot of the HD footage that people are shooting these days."
TIP: Be careful not to affect your principal lighting. "I am primarily speaking of live action, where you are not doing a separate matte pass. We do digital effects here but we also do quite a bit of miniature work and practical effects, and we shoot actors. We have the ability within motion control photography to shoot separate matte passes — and for that we are basically lighting whatever screen we are using on the day but turning off everything else. All the practical lights, beauty lights go off, any other ambient lighting that's lighting the subject is turned off,  and what you are getting is green backing with a very dark silhouette of what you are pulling a matte against."
TIP: For shots using tracking markers, use a color that contrasts. "If you are using bluescreen, use red tracking markers, and keep the markers away from the edges of your subject so you don't have to go back and roto the markers out".
TIP: Adjust the stop depending on what you are shooting. "When you are shooting on a stage and shooting on film it helps having the composite screen lit a half a stop brighter than the principal lighting. And as for HD, a half a stop under is a good rule of thumb so as not to blow out the screen's color information."
TIP:  Use bluescreen outside because it lights more easily. "But more importantly if you have spill on your subject at all it marries in with the blue spill from the sky. We typically use digital blue or digital greenscreens; there is a chroma key green, which is like a darker forest green, but it's nowhere near as hot and vibrant as a digital green. We also do contrast matte passes, so we'll put up a 10 percent gray or white screen, depending on what we are trying to pull a matte off of."
TIP: As long as the subject your shooting is covered by whatever matte screen you are using, you're fine. "The main point is to have coverage of the subject's edges to avoid roto work. Anything that is beyond the subject's edges can be garbage matted out. If you are doing a shot on stage and you are shooting up at your actor and have the ability to cover the entire background that's great… but it you can't get that large of a screen rigged, you don't need to put up a screen to cover everything top to bottom. Just cover what you are shooting. We use 4'x8'cards all the time and we'll block out and rehearse the scene and cover the subject so you don't have to get the grip department to put up this colossal screen."
TIP: Match your background plate's lighting! "Lighting your composite screen correctly and the proper coverage is instrumental for a good composite, but the most critical component of a good composite is an excellent lighting match. Regardless of how good the matte pulls are, if the lighting of the subject doesn't match the background, you're left with a shot that will feel composited."
New Deal's mantra is to do it as simply and practically as possible, and Gratzner points to a recent sequence they did for Night at the Museum: Battle of the Smithsonian as an example. In the film, there is a sequence where the Wright Flyer — the Wright brothers' plane — is flown by Amelia Earhart from one side of the Air and Space Museum to the other. The whole scene was designed to combine live action of actors Ben Stiller and Amy Adams, shot against a greenscreen, with a composited miniature background. For wide shots, the Wright Flyer itself was animated and composited into the miniature backgrounds by Rhythm & Hues.
"My partner Ian Hunter was brought in by the film's director, Shawn Levy and the film's visual effects supervisor, Dan Deleeuw, to design a new previs for the sequence. New Deal Studios' digital department used Maya to build and animate the scene. We then built the miniature museum — an 80-foot long model — and shot it using a motion control camera running off of the animation from the Maya previs. There were a number of shots where there was just no way to get the ceiling and the motion control camera rig in the model at the same time, so we added back in a digital version of the ceiling from the Maya model. We put greenscreen above and on the ends of the set so we could do these extensions."

DO YOU FEEL LUCKY?


Semerad (www.semerad.tv) in New York City works with greenscreen about 30 to 40 percent of the time — sometimes as visual effects supervisors, sometimes as directors and often as compositors. Studio owner/ creative director/VFX artist Johnnie Semerad offers these suggestions…
TIP: Avoid greenscreen if possible. "Try to shoot as much as you can in the environment — things cast real shadows and you have real reflections, which is always a plus."
TIP: Shoot the backgrounds plates first. "Get the performances and then match the greenscreen to the background plate, so the lighting matches, the eye angles match, everything has to match. We do a lot of things where we put people into stock footage and if you can do the edit and pick the background plates to match one to the other rather than anticipating, it's always better."
TIP: Don't mix colors. "Sometimes they paint with two different colors of green. Make it all the same green. The worst is when you look at the set and they're like "we ran out of greenscreen so we used blue. When we ran out of blue we went to black. That section over there where there's nothing you'll just have to rotoscope that. Sometimes stuff like that happens on location or in a small town. As long as the light is good we can fix that type of thing."
TIP: When shooting feet, try to get as much of the real shadows as possible. "If he steps and casts a shadow on the ground, I try to use that as much as possible. Real is always real and that always looks better than making your own shadows."
TIP: When working with talent who are only on set for a limited amount of time, be ready to go before they even walk on set. "They show up and have to leave so many hours later. So you have to prelight, pre-everything, with body doubles because access is so tight."
The studio has been working on the Take 5 campaign for the New York Lottery out of DDB, which features a man (A Little Bit of Luck) with a big head and out-of-proportionally small body, which is real. The studio had to shrink the actor's body and legs in Inferno to get the look the agency wanted.
According to Semerad, who was VFX supervisor on this campaign, the only option was shooting greenscreen because they were playing with the main character's proportions. "His head is normal size, his body is half size and his legs are quarter size, so his proportions have to change and there is no way to shoot that on location," explains Semerad. "We shot all the background plates first, did a rough edit, then went in and covered everything with him. We then had to pull the key on him, cut out his head and cut out his jacket so we could adjust his proportions."
In one of the spots, the Take 5 character is in a diner talking about the lottery and interacting with other characters — all have the word "luck" in their name, such as Beginner's Luck, Down on His Luck and Hard Luck. Those actors were shot practically on location. The main character was shot in front of a screen and on a green stool. "You are on set with a switcher and you have the background plate," explains Semerad.
The actual stool was shot in the diner with a prop guy underneath making it turn and rotate with rods. Back at Semerad, artists composited the greenscreen footage and the background plates, which were shot on 35mm. Jon Watts directed this piece.
"We work on Infernos," says Semerad. "They are really good at handling footage. They can pull keys and we have a lot of tools for edging. We basically shrunk him down and tracked him."
Semerad says the best thing about greenscreen is you do all that work, show it to your mom and she's like, 'What did you do?' "That's the best compliment you can get."

SHILO RUNS WITH BROTHERSISTER


New York-based Andre Stringer, co-founder/creative director/director at Shilo (www.shilo.tv), has directed his share of greenscreen shoots, most recently it was a music video for the band BrotherSister, which was actually one of his more simple greenscreens jobs.
Here he shares some of his real-world best practices…
TIP: Use props when appropriate. "Anything the actor could interact with that's real is extremely helpful because the more you put in the scene that is an actual element, the more easily it is to populate a scene. You have to make less later. Also, give the person who is acting something to vibe off of. Instead of saying, 'Over there is going to be this huge tree that's going to reach out and tickle you,' have someone reaching out with a green hand to tickle the person."
TIP: Create a ground plane. "We've done quite a few music videos, and things you can do on set that take the burden off creating all of the realism in post are huge. It's really cool to make the ground plane of what you are actually working in and use that practically. If you are going for realism, it makes more sense to put your energy into the photography. This is one of the life lessons that we've learned when realism is the end goal....of course that is not always the look you're going for, but in those instances, where you want to go for this, it's a really important factor."
TIP: Don't underestimate the importance of interactive lighting. "It seals your whole point of view, which is sometimes lost in the process of making heavily post treated work. You sort of lose it to a more generally lit point of view or an ultra high contrast point of view. It's great when you find cues in your photography while shooting. Focus on the lighting and not just pragmatically — your DP will make sure the greenscreen is lit correctly — think about what kind of story you are trying to tell and what vibe and tonality you want. When you are there that day, it's very reactive. You can move lights around and see how it works."
TIP: Don't overlook the interactive quality of the principal light. "Beyond lighting the screen evenly, the principal lighting direction you are doing for your subject and the quality and interactivity of the lighting are sometimes overlooked. When you are working with a virtual set for standard television, you tend to light your subject so it's nice and clean and the edges are nicely defined so you can pull a key — it's all about the technical — but in reality we use greenscreen more for the finer details, but we'll light it so we get the best looking composite; something that most matches what we are actually thinking of for the background and environment around them."
Shilo recently worked on a music video called Still Run for the Australian group BrotherSister that was shot greenscreen with a cyc, a shoot that Stringer calls "incredibly simple."
They shot a man running on a green treadmill with a guy standing on a ladder waving a 2K light on top of him. "The light just rolls over his shoulders creating the feeling like he was running through pools of light, which we used as the end lighting style for the piece that we made," he says.
In the video, which was shot with a Phantom HD camera, the man runs through a number of environments and landscapes, and the weather changes throughout. He is seen running through grass, water and snow. Shooting feet on greenscreen is typically a tough job to composite. "Our principal character never ran through anything; he just kept running in the same place, with the light moving on top of him every 10 seconds."
Shilo used Maya to animate a 3D version of the runner to match the same run cycle as the guy on the treadmill. "We used that character as the dynamic force that then affected the water in his run," explains Stringer. "We tracked the whole run, which wasn't much of a track because he is just running in place. We just matched the pacing of the world moving underneath him."
It's the 3D person that runs into lightning bugs, which cascade around him, and interacts with falling snow. "You have to make a proxy for the live action, which is flat and doesn't have dimension," says Stringer. "Something could hit his arm, but the particles might be in front of him instead of behind; it wouldn't match up correctly. Also you want things to roll around him correctly."
For the most part, the backgrounds are 2D matte paintings created by Shilo. "Even in the foreground where it needs to be more dimensional, we made matte paintings and wrapped them around really basic geometry in Maya," says Stringer. "We also used pretty traditional graphic compositing techniques to create the world around him. We weren't going for 100 percent realism; we wanted fantasy realism."
Shilo also created miniatures of the backgrounds, such as the hills, landscapes, trees and where water was pictured. "They were miniatures that we shot as still photos — we broke them apart and made matte paintings out of them."