How to set up a green screen that actually keys cleanly

Most disappointing green screen results are not caused by the software. They are caused by a screen that was creased, unevenly lit, or two feet behind somebody’s head. Get the room right and almost any keyer produces a clean result; get it wrong and no keyer will save it.

This is the practical setup, in order of how much difference each thing makes. The green screen guide covers why any of it works, and removing a green screen in any app covers what to do with the frames afterwards.

Distance first

If you change one thing, change this. Move the subject away from the screen.

Distance does three jobs at once. It stops green light bouncing off the screen onto the subject, which is the cause of the green rim everyone complains about. It lets you light the subject with lights that are not also hitting the screen. And it puts the screen slightly out of focus, which softens creases and unevenness before the software ever sees them.

A metre is the minimum that makes a real difference. Two or three metres is noticeably better. In a small room, the practical version is to put the subject as far forward as the camera position allows and accept that you will do more spill suppression afterwards.

The screen itself

Matt, not shiny. A glossy surface reflects your lights back as bright spots, which are a different colour from the rest of the screen and key differently. Matt fabric, matt paper or matt paint.

Flat, not creased. A crease is a shadow, and shadows are the hardest part of a screen to key even with a good keyer. Options, in increasing order of reliability: clamps and tension, a steamer, a roll of seamless paper, a painted wall.

Opaque. A thin sheet with a window behind it will have a bright patch. Double it up or hang something behind it.

Big enough with room to spare. You want screen visible at every edge of your frame. Cropping in later is easy; inventing screen where the frame ran off the fabric is not.

The fabric being expensive matters much less than any of the above. A pulled-tight bedsheet in a strong matt green, lit properly, beats a professional screen lit badly.

Lighting the screen

The goal is an even field, not a bright one.

The standard arrangement is two soft lights, one on each side, at roughly 45 degrees to the screen, placed so their beams cross over the middle. Because each light falls off across the screen and the two falloffs run in opposite directions, the result is far more even than one light in the middle could ever be.

Move the lights back rather than up the power. Light falls off with the square of distance, so a light close to the screen is much brighter in the centre than at the edges, and a light further away is gentler across the whole thing.

Do not overlight the screen. A screen brighter than the subject throws more spill and can flare around the edges of the subject, eating fine detail such as hair. Roughly equal to the subject, or slightly under, is the target.

Lighting the subject

Light the subject as you would anywhere else, with lights aimed at the subject and not at the screen.

A key light slightly off axis and a softer fill on the other side is the usual pair. Flags, barn doors or simply moving the lights further forward keep them off the screen.

If hair matters, and for a cutout it usually does, add a light behind and above the subject aimed at their shoulders and the top of their head. This separates the hair from the backing and gives each strand a bright edge, which is exactly what a key needs to resolve it. Professional headshot background covers the portrait lighting side in more detail.

Match the direction of your lighting to the background the subject is going onto. A subject lit from the left composited onto a scene lit from the right is the single most obvious tell in a bad composite, and no amount of keying quality fixes it.

Camera settings

Manual everything. Fix the white balance, the exposure and the ISO so that consecutive frames key identically. Auto white balance shifting between frames means the key colour changes under you.

Lowest usable ISO. Noise lives in the chroma channels and makes edges crunchy. It is the most common reason a phone photo keys worse than a camera photo of the same setup.

Avoid heavy compression. Chroma subsampling, which most cameras and all phones apply, stores colour at half resolution. It is usually survivable for a still, and it is why professional video work uses formats that do not subsample. If your camera offers RAW for stills, use it.

Do not sharpen in camera. Sharpening puts halos along edges, and halos key badly.

In a small room

Not everybody has three metres. The compromises that cost least:

• Put the screen against the wall and the subject as far forward as the lens allows.
• Use a longer lens from further back rather than a wide lens from close, which also flatters faces.
• Light the screen from above and the sides with whatever you have, and accept a little unevenness, which tolerance will cover.
• Expect more spill and plan to suppress it. Green screen spill covers the fixes.
• Consider a blue screen if the room is small and the subject has any green in it, because you will have less room for error.

For a product rather than a person, a small space is much easier: a table, a sheet of green card curved up the back so there is no corner line, and one light either side gives a near perfect field. Raise the product on a small clear stand if you can, because it lifts the contact shadow off the backing.

Green or blue, and what else works

Green is the default because human skin is furthest from it and because digital sensors record more green than anything else, so the green channel is the cleanest one in the file. That is a real advantage and it is why most screens sold are green.

Blue earns its place whenever the subject contains green. A costume, a plant, a bottle with a green label, a brand whose colour is green: any of those turn a green screen from an advantage into a problem. Blue is also kinder to blonde hair, which picks up a green cast very visibly, and it throws less obvious spill on skin, because a slight blue cast reads as cool light rather than as illness.

Neither is sacred. The rule is simply that the backing should be the colour least present in the subject, and for product photography that often means neither green nor blue. A bright magenta card behind a green plant keys better than any amount of fighting with a green screen. A deep orange behind blue packaging does the same job. The tool on this site keys whatever colour you point it at, so the decision can be made by what is in front of the camera rather than by what was in the equipment bag.

One thing to avoid whatever the colour: a backing close to the subject’s own tones. Grey and white backdrops are excellent for portraits and terrible for keying, because skin, hair and clothing all contain them.

Checking before you shoot fifty frames

Take one frame, key it, and look at three things: the background at the edges of the subject, any shadow of the subject on the screen, and the hair. Fixing the room takes two minutes; fixing fifty bad frames takes an afternoon.

A shadow of the subject visible on the screen means they are too close to it or the lights are too close to them. A green edge means the same. Dark corners on the screen mean the screen lights are too close or too few. Each of those has a physical fix that is faster than any slider, and the fix stays fixed for the rest of the session rather than having to be applied to every frame afterwards. Ten minutes spent on the room at the start is the cheapest time in the whole process.

The steps, in short

1. Hang the screen flat. Pull the fabric tight and clamp it, or use paper. Creases cast shadows, and shadows are the hardest thing on a screen to key. A steamer removes fold lines from cloth in minutes.
2. Put the subject well away from it. At least a metre, two or more if the room allows. This prevents green light bouncing onto the subject and lets the screen fall slightly out of focus.
3. Light the screen evenly. Two soft lights, one either side at about 45 degrees, aimed so their beams overlap across the middle. Check the corners are not darker than the centre.
4. Light the subject separately. A key light and a fill for the subject, pointed at the subject and not at the screen. Add a light behind and above aimed at the shoulders if hair matters.
5. Set the camera manually. Fix the white balance, the exposure and the ISO. Use the lowest ISO you can, because noise in the green channel is what makes an edge crunchy.

Questions

How many lights do I need for a green screen?

Four is the classic arrangement: two on the screen and two on the subject. Three works if you use a reflector instead of a fill light. Two can work in a small space if there is enough daylight, but you will spend the time you saved on fixing the key.

How far from the green screen should I stand?

At least a metre, and more if the room allows. Distance reduces the green light bouncing onto you and lets you light the subject without spilling onto the screen. It is the single most valuable change in most setups.

What is the best green screen fabric?

Matt, opaque and wrinkle resistant. Muslin is cheap and creases, polyester is more wrinkle resistant, and collapsible pop-up screens are convenient and small. A roll of green paper is the easiest thing to get perfectly flat. What matters is matt and even, not the brand.

Can I paint a wall instead?

Yes, and it is the most reliable option if you have a dedicated space. Use a matt emulsion in a strong green; several paint manufacturers sell a chroma key green. The flatness of a wall solves the crease problem permanently.

Do I need a green screen for photos, or will any colour do?

Any colour the subject does not contain will do. Green and blue are used because skin contains neither. For a product shot, pick whatever is furthest from the product's own colours.

Why does my key look fine in the middle and bad at the edges?

The screen is lit unevenly, which is almost always because the lights are too close to it. Move them back, or further out to the sides, so the falloff across the screen is gentler.