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August 2014
Issue: July 1, 2010

THE KEYS TO SHOOTING GREENSCREEN

By: Randi Altman
With keying software more advanced and stable than ever before, effects pros working with green, blue or other color screens can now focus on the job at hand. Lighting is still important, of course, but pros realize they can get away with a little more thanks to today’s tools.
Meanwhile, DSLR cameras are making their way onto greenscreen stages and come with their own set of challenges. While it provides a gorgeous picture, it is a compressed format. Some have solutions that include existing tools meant to deal with HDCAM footage, others go in knowing what they are up against and work around it.

GREEN ON THE GO

Shooting green at different locations comes with its own set of challenges, and visual effects pros need to be prepared for anything.
“There are such a huge variety of situations you will be in when shooting greenscreen,” explains creative director John Bair of NYC ’s Phosphene (www.phosphenefx.com). “One day you might walk onto a set that’s got a perfectly-built and perfectly-lit wall of green. The next day you need to pull off a shot very quickly and just throw up some green, whether it’s the craft services area or anywhere.”
A situation just like this came up recently for Phosphene and Bair while they were working on HBO’s original movie You Don’t Know Jack, about Dr. Jack Kevorkian and starring Al Pacino. The movie looks back at how Kevorkian found his way into physician-assisted suicide and includes interviews the doctor did with patients in the late ‘80s and early ‘90s. A big part of the visual effects work was shooting Pacino (playing Kevorkian) greenscreen and compositing him into that VHS interview footage.
“There was a day where we were planning to shoot greenscreen in a certain — and not ideal — location later in the day,” explains Bair. “Suddenly we realized there was time to shoot it right then and there, so we found a small side room in a restaurant across the street; they let us put up a greenscreen and we shot some scenes with Al Pacino — all of which made it into the film.”
The majority of You Don’t Know Jack was shot on 35mm; greenscreen was shot on 35mm/24fps, as well as on HDCAM. According to Bair, “We shot HDCAM at 59.97 to match VHS sources, and we wanted to exactly match the motion and all the artifacting you would get when shooting interlaced.”
Much of the greenscreen that was shot on 35mm was for “a tremendous amount” of driving shots done on a stage over the course of two days. The biggest challenge, says Bair, was shooting everything in advance and matching angles. “A lot of those scenes took place in the late ’80s to the early ‘90s, and every character had gigantic eyeglasses. We had to make sure what we were seeing through the glasses was distorted in an appropriate way, even though it was shot on green. So there was a lot of manual tracking there to offset the backgrounds we were putting in.”
How different is it shooting HDCAM as opposed to 35mm? According to Bair, “There are some general rules we follow in terms of how bright the green should be, but generally when shooting HDCAM, we are more concerned about the foreground subjects and making sure we are not blowing anything out and not overexposing the background.”
What concerns Bair most is that HDCAM is a less forgiving format if anything is overexposed in terms of keying. When working with film, Phosphene makes sure the background isn’t overly lit, “but film has such a great response curve, we can deal with those issues much better in post if they happen to occur.” Thankfully this didn’t happen on You Don’t Know Jack.
In terms of trends, Bair says that thanks to how far software has advanced in recent years, the key is matching lighting, “and worrying a little bit less about perfect, ideal keys because the software can handle sub-optimal greenscreens. The software can work around limitations you have at the time; it’s much more about planning the shots in advance, and storyboarding is always a great idea.”
With DSLRs becoming more commonplace in production, it was only a matter of time until they found their way onto greenscreen shoots. Phosphene has been working on Vanishing on 7th Street with director Brad Anderson.
“We are doing tons of effects for that; and we’ve shot a ton of greenscreen elements with the 5D Mark II,” says Bair. “It’s amazing in many ways, if you know its limitations. It’s a compressed format, which is always a challenge, and that is maybe the biggest difficulty with it. You can also have a little aliasing just due to the way it’s capturing images, and it’s basically removing lines of data to go to HD from the full sensor size. So if you have very sharp images you can get a little bit of aliasing.”
They have found that some software is able to compensate for HDCAM compression, and that going through the same process you would for HDCAM helps in terms of doing an initial pass, which will greatly remove some of the artifacting before pulling a key.

GREEN & BLUE

Simon Mowbray, creative director/visual effects supervisor at SF’s Ntropic (www.ntropic.com) feels the biggest challenge when working with greenscreen, bluescreen or any processed background, is that budgets are tight, shooting schedules are compressed, and there isn’t always enough time to light the greenscreen properly. “We always supervise shoots,” he says. “Almost every DP I’ve worked with knows how to light a greenscreen, that’s not the problem. It’s more that often there isn’t [the] luxury of time to finesse the processed-background lighting, because obviously the foreground takes precedence”.
Ntropic has also worked with DSLR cameras recently. Mowbray says that while there are limitations to the format, there are also benefits. “The Canon 5D’s H.264 compression can be a challenge for keying. Regardless, it still shoots a beautiful picture, which is half the battle. Also, its ability to shoot such a narrow depth-of-field can be used to smooth-out green-screen unevenness. Even so, I still prefer to work with the higher-resolution formats for compositing.” He likes the Genesis when shooting digital and is eager to see the new Red cameras, but “film can be better in some respects,” he says. “You have more latitude.”
When working with greenscreen, Mowbray and Ntropic recommend to DPs that they shoot it at key or as much as one-stop below key for film. “With bluescreen it’s as much as one-and-a-half to one-and-two-thirds below keylight level. Whenever we shoot digitally we make sure all the sharpening filters are switched off, so even though the footage may look a little less sharp on-set, the composite edge will be a lot cleaner.”
For a recent Franklin Templeton spot out of agency Collaborate, Ntropic was called on to produce and post the greenscreen-heavy Global Expertise, which was directed by Ntropic creative director/founder Nate Robinson. The project is a combination of live action and 3D matte paintings. It features actors captured against greenscreen and pictured in cities around the globe — the CG environments were created in-house at Ntropic.
The viewer sees people in front of icons representing these international locales, such as a pagoda (all CG), the Eiffel Tower, a rickshaw, the Sydney Opera House and Big Ben. These elements were either shot over greenscreen, or sourced as stock, and then integrated into 3D matte paintings.
In the Big Ben shot, the uneven sky was used as the bluescreen. “It was a combination of rotoscoping and pulling keys from the sky,” describes Mowbray. “However, the flexibility of today’s software makes guerrilla compositing possible and believable, just with a longer turnaround.”
A more traditional bluescreen shot is where a newswoman is pictured on a screen below a stock sticker on the side of a building in India. She was shot bluescreen and composited in. A complicated car shot was done greenscreen. This was a matter of “pulling keys through glass, which is always tricky,” says Mowbray. “We ended up having to add reflections back into the glass of the car, and the background was a big 3D matte painting [of Sao Paulo]. All the reflections in the windows were added as a 3D element, which is a big part of compositing now.”
Ntropic called on Autodesk’s Inferno, Flame, Toxik and Smoke for the piece. They also used Autodesk’s Maya. “We have a really solid pipeline between Maya and Inferno in that we use the 3D capabilities of both, which is an unusual way to use the Flame/Inferno suite,” he says.
Greenscreen/processed background is a great tool, sums up Mowbray. “In years past you’d almost always shoot greenscreen locked off. That’s really not the case anymore. The tools are such that it is much easier to build 3D worlds. If the camera has to move or dolly or crane, it’s not such a problem for us to build a 3D matte painting to make a world that works in 3D. It’s a lot easier for us to build a dimensional-perspective-based set.”

A WINNING TICKET

Flame artist and senior editor Tom Fulks, of Detroit’s Grace & Wild (www.gracewild.com), has been working in this business for 30 years, and says the basic rules of working with greenscreen have always been the same: it’s all about lighting and separation.
He, like the others we spoke to for this piece, is happy about the recent developments in software. Having access to a large amount of adaptable keyers has made his life easier. “What’s changed is the technical prowess,” he says. “The Flames, the Nukes, the plug-ins… those are the things that have evolved.”
Recently Fulks and Grace & Wild were called on for a commercial introducing new Money Match instant tickets from the Michigan Lottery via agency SMZ. Shot with a Red camera, this spot promotes three different tickets — one yellow (worth $20K), one blue (worth $200K), and one green (worth one million). In the piece, individuals from different walks of life are pictured with backgrounds representing the different colors of the cards.
“The director [Anthony Garth from Avalon Films] wanted to shoot on white, but I convinced him, with some help from the agency, not to,” explains Fulks. “After viewing audition tapes of the older people with white hair, the client looked at me and asked, ‘Can you key that off of white? My answer was ‘I really can’t. I need a color back there.’”
Because two of the prominent colors of the spot were green and blue, Fulks decided to shoot on redscreen — Grace & Wild has its own 140x108-foot stage with 220-foot hard cyc. “Everybody was cool with that because it was the complete opposite of the colors we were going to use — yellow, green and blue. Unfortunately there is red in skin tones and red in yellow, but it gave me the separation I needed for hair and things that are more difficult so I didn’t have to rotoscope. Rotoscoping never looks good with hair — you need to get that separation.”
To hammer home his point, Fulks mentions that two-thirds of the actors were either wearing all green or all blue. “We didn’t have time to paint different screens and change them out, so we used red as the base color for keying. It’s not optimum. I still had to do a lot of work on it, but it’s a hell of a lot better than white.”
Thanks to the keying capabilities on these systems, shoots are not limited to green or blue anymore, says Fulks. “Flame has a bunch of keyers, so I can go in and do a lot of things. It’s just getting as good a separation as you can from the background to the foreground.”
A big reason the one-day shoot went smoothly was because LA-based DP Peter McKay knew how to light for redscreen. “Since most skin tones are the same shade of red, what Peter and I did together in lighting was try to get as much separation as we could,” says Fulks. “Maybe over-lighting a little bit of the skin so it would pop more so I could do more of a luminance key.”
African American skin tones have even more of a reddish feel. Fulks points to one scene of a girl on rollerblades. “We had to pay a lot of attention to lighting the background and foreground elements, so I could get good separation. That was my biggest challenge, making sure I got good clean keys off the skin.”
There was actually one scene that wasn’t shot on red, but shot on white. It was a wide shot of a man and his RV. This is where shooting on white actually did make sense. “Most of the actors are static, except that one guy,” explains Fulks. “I ended up creating a difference matte, then rotoscoping him off the white and changing the background to blue. I then painted the white RV blue.”
Fulks had his hands full. He ended up having to do 18 comps and three different 3D pages in a week. The spot spent four days in offline with creative editor Steve Persin (Griot Editorial, a division of Grace & Wild), which was critical to get an approved offline with so many comps and a tight deadline.  Fulks used Flame for the VFX and performed the final finish in Smoke. Grace & Wild’s VFX arm, Division X provided the spot’s rotations and ticket animations via Maya.
While Fulks likes film, he prefers to work digitally because he feels it’s cleaner. “Low-grade film is great, but not as great as HD or copying a 4K file from a Red file coming out of Scratch. It’s just cleaner with less grain. It doesn’t mean I think it looks better, it just keys easier when you are shooting green.” He has yet to work with a DSLR on a shoot.

THIS OR THAT

Framestore (www.framestore.com) in London recently worked with blue, but it wasn’t a screen. They completed visual effects on a Kia spot, This or That, out of David & Goliath, LA, that features 45 photorealistic rapping hamsters that had actors wearing hamster-proportioned suits and blue over their faces, arms and legs. The studio then added CG hamster appendages.
In the spot, these “street” hamsters rap to Black Sheep’s 1991 “The Choice is Yours” track and are shown enjoying all that urban life has to offer. There are even a couple of uptown lady hamsters turning their nose down at the others. The three main hamsters rap for viewers, singing, “You can get with this [a Kia] or you can get with that [a toaster].”
The spot was shot on location, not in a bluescreen studio. “Each character was shot with proportioned bluescreen hamster suits and clothing on top,” explains executive producer Tim Keene. “Where possible, clean plates [i.e. with no action], were shot, so that we could ‘key’ off the blue areas of the suits and restore the background for any areas overlapping where our CG was going on top. By having the hamster-proportioned suits you get some indication of the light direction and the approximate shape of the hamsters for framing. Additionally, we had specific tracking markers on the bluescreen suits so we could body track the orientation of the heads, hands and legs to apply our CG to it.”
Diarmid Harrison-Murray, head of CG, says that in the end, having blue hoods, hands and legs wasn’t really a benefit. “Being on location and therefore not able to fully control the lighting, meant that not much of it could really be pulled as a key, so we ended up having to hand roto this stuff out anyway! Probably in hindsight, we would have been better off with a much more neutral color, not blue or green, as not only did we have to roto the suits off, but we had to also paint out any blue motion artifacts.”
Framestore had to accomplish a lot in a short amount of time — over 50 shots in a matter of two to three weeks once they had the final renders. “Prior to the final stages, we of course had huge amounts of animation to get approved,” reports Keene. “Late changes in animation and on the look of the hamsters are an occupational hazard. With this in mind, we tried to ensure that the compositing process was as efficient as possible, which is one of the reasons for using the Nuke for its capability to use the raw render data CG and it not getting compressed in anyway.”
For the fur, Framestore developed a new set of fur grooming tools to work with Houdini’s native renderer, Mantra, rather than the previously-used RenderMan.
Since the main characters have CG faces and are rapping to a song, making the hamsters’ mouths move in naturalistic ways with the music was key. “That was quite a challenge,” says Harrison-Murray, “because you’ve got two opposing forces: one is trying to maintain the naturalistic shapes hamsters make, and the other is trying to mimic and match that of the human rap artists. It’s always a balance between not losing the hamster and yet giving a convincing singing performance that we recognize. To find that balance is not an exact science, so it’s a case of finding a happy medium.”
This or That was shot on 35mm with some background “reportage” material shot on the Canon 5D, such as the skyscrapers.
Keene likes the DSLRs and feels they are getting better and better. “They have fantastic resolution of imagery and ease of use. You do have to bear in mind some of the limitations, for example: tracking. Rolling shutters, as used on the 5D and Red, cause an offset between the top and bottom of the image when panning, which becomes problematic when we’re tracking the cameras in CG. There are plug-ins and tools we can try to use to correct that but it’s best to be avoided if possible.”
Even though this Kia spot didn’t use screens, other jobs at Framestore do, and while Keene agrees that keying software has gotten better, if the piece isn’t shot correctly it will always be a challenge. “In extreme cases where it simply doesn’t work, you have to go back and hand roto the elements. Where we see our role, in particular, is getting involved at the early stages to avoid this. From advising what needs to be shot in front of green-/ bluescreen, to helping [get] the exposure and correct light balance.”