In my previous one itemsWe discussed the whys and whys of shooting people in green suits or not, and got into the subject of greenscreens.
Making a green screen shot look convincing is a major challenge even for experienced VFX artists and post offices – the challenge should not be underestimated or taken lightly. However, I will try to provide some guidelines in order to give you the best possible results with the least amount of pain.
The first and foremost point for everyone is to have a VFX supervisor on the set. Even with a low budget production, you can afford to oversee the compositor on set (many composers are actively seeking on-set experience). Ideally, it should be the same person handling the green screen footage in the post.
This is me and the team and a nice flat and even green screen shot at Broadley Studios, Marleybone
Shoot or make the background first – If it is footage or a still image, you need to record it on site before recording the green screen. If it's CG or a digital matte (a still image usually created in PhotoShop), have at least one mock-up or a work-in-progress version ready before shooting the green screen.
This is because you need to adjust the lighting and shadows of your foreground cast members to match the lighting and shadows of the background. It is almost impossible to convincingly change the lighting beyond subtle changes in the post.
If your background is outside daylight, capture your green image in daylight. The sun has a diameter of 1,390,000 km and is 149,600,000 km away. Unless your budget allows you to place lights at that size and distance (which requires at least a Type 2 civilization) Kardashev scale) then using actual sunlight is your best option. Studio lights never look like sunlight.
Shoot RAW or as close to RAW as possible
Many DSLRs use h264 compression, which looks good on a standard shot but severely affects the compression. ProRes 422 means the resolution is your chroma (from which the key is largely derived) half of your full camera resolution. ProRes 4444, DNG, BlackMagicRAW, or ArriRaw are good options if you can get them.
Another trick is to shoot at a higher resolution than the final picture so you have more pixels for important details.
Make your screen as flat and even as possible
Make your green screen as flat and even as possible. Flat and uniform in every way: material, uniform texture, uniform color, free from wrinkles, clean, free from shadows, evenly lit, free from bright lights. You will never get it 100% perfect, but the closer you get the better it gets.
This green screen of "Trollbridge"From director Daniel Knight, wasn't flat or smooth at all and it was quite difficult to get all of the eyebrow and beard details on our heroes. High winds also meant the screen and markers were moving.
Place your green screen as far away from the subject as possible
Correct, so that the foreground is lit in the same way as the background plate is lit. But you want the green screen to be evenly lit. So there has to be enough distance so that the actors can be illuminated correct cinematic lighting and in a manner that is consistent with the intended background; and so that the green screen is completely flat and evenly illuminated.
You also don't want contamination from one to the other – shadows cast on the green screen by your key light and the dreaded green bounce light.
Green bounce is awful, it means the color of the edges is green which makes it difficult to get a mat. When you do this the edge is green and needs to be recolored convincingly (which is difficult). If the subject is backlit this can help as the backlight kills some of the green light reflected off the screen, but for the love of all that is sacred, a subject that needs to sit in front of a dark background, not behind illuminated . It will always look ridiculous ("When she's standing in front of a black spaceship in the dark, where does the light on her hair come from?")
Shave everyone's head
Keying hair is difficult. Shave everyone's head and make them part of the story if your script and cast allow. I will be the first to admit that this option is not always practical.
Avoid foreground elements that are highly reflective or the same color as the green screen
Of course, if your main character is a green alien, use a blue screen, as well as if they're in jungle camouflage or something. A reflective material is the same color as the reflected material – which likely means it will turn green or blue and will not match your screen. A show with a green alien and a man in a shiny suit might want to come up with one different approach.
Do not use a green screen
If you don't need it, don't use it. Really think about whether a shot has to be a green screen at all.
Screenshots are a really good example. You won't believe how many green screen shots are basically just phone screens, computer screens, television screens, etc. The reason for this is that many productions cannot decide in advance what exactly will be shown on the screen. As an indie filmmaker, your superpower is that you can make decisions without waiting for 15 different executives to sign them off. So use your superpower, decide what's on these screens and have them ready before you shoot! This is the low budget equivalent of the 360 LED environments used on the Mandalorian (see link above).
BTW, if you record your screens live, please don't change your mind later – it will be nigh on impossible (believe me, I had to!) To replace a filmed graphic with something else, especially if it is a graphic acts animated or people come by in front of the screen – if so, fill it with green or maybe just shoot them off (check with your manager on set before making the call).
I could write an entire article about tracking markers, but someone else did. But the short version is here: the green screen has no features, and when the camera is moving, the software needs some high-contrast points to snap into place so it can replicate the movement in the background. These markers must be:
- Simple points or circles (That way, the center will still be apparent when they are out of focus). Forget funky shapes, letters, or crap.
- Not in the way of hair or other tricky details – Obviously, by sticking markers on it, you are breaking the beautiful evenly green screen. So try to keep them where people's hair and the like are not.
- Identifiable – Make the pattern irregular so you can tell one marker apart from another
- Not bigger than they need to be – depends on the size of the shot, but large markings are not helpful. They need to be just big enough to get high contrast in the final image.
- Don't flutter in the wind – If the wind is flapping on the green screen, no tracking markers on it are useful (as they measure fluttering wind movement, not camera movement).
- Not reflective – If they are reflective, trace the reflections on the marker, not the marker itself
A big thank you to Chris Poulay, Matchmove Lead at One of Us, for his marker advice.
Again, it is not easy to make green screen shots look convincing and should never be underestimated. However, follow these guidelines on set and it will at least be doable.
About Daniel Mark Miller
Director Daniel Mark Miller is a British-Iranian VFX artist, screenwriter and filmmaker.
Daniel started writing at a young age and has always had a taste for the strange, the fantastic and the outsider. Daniel has continued to write and work independently for over 10 years as a professional digital compositor for important feature films and TV shows such as Baby Driver, The Crown, Good Omens, Pinocchio, Giri Haji and Morbius.
He recently won Best Short Screenplay for the screenplay for "Broken Toy" at the New Renaissance Film Festival 2020 and is currently working on a promotion for the short film.