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HOW TO USE GREEN SCREEN?

As far as your imagination can go, green screen can get you there! It is definitely worth the investment in your film production. The only limit is your imagination!

Green screening has become one of the most effective ways to create scenes that were unimaginable in the not-so-distant past. But beware, there are common mistakes and they can be avoided. We’ll start off explaining how does green screen work and move on from there into more advanced concepts.

This guide is meant to give you the tools and know-how necessary to create fantastic and realistic effects using the magic of the green screen. We may not all have James Cameron’s budget, but the basics of his chroma key techniques remain true no matter where you are on your filmmaking journey.


What is chroma keying?

Green screening, often referred to as chroma keying, is the ability in post-production to key (or adjust) the chroma (colors) that are visible in the layer of any shot. For example, if you make the color green invisible in one layer, then the footage in the layer below that clip becomes visible. This is the essence of green screening.

The most common colors used are bright green (“green screen”) and bright blue (“blue screen”). The main goal here is to create as much color difference between the backdrop and the actors as possible. The importance of this distinction between foreground and background will come up time and again, as most of this guide consists of techniques intended to achieve that end goal.

Why green or blue? These are the most common because bright green and blue are the best for creating contrast against your actors skin, hair, and clothing. Green is the most commonly used, can you guess one reason why? The really short answer is that green screens are green because people are not green. In order for the effect to work, the background must use a colour that isn't used elsewhere in the shot – and green is nothing like human skin tone. ... And human skins reflect broadly similar ratios of each colour of the spectrum.







For the Set

Does everyone remember our main goal?! That’s right: create as much color difference between the backdrop and the actors as possible.

Backdrop

The keys to creating a backdrop are the color selection and creating as smooth a surface as possible. Angles and shadows are your enemy, because they create colors in the background that come closer and closer to those found on your actors.

There are a few options for your backdrop. You can (1) use green screen paint, (2) use a large green sheet, or (3) build your own wall and paint it.

Chroma Key paint

Chroma key paint is available online. This method works if you:

  • Have a relatively static shot (camera position and angle won’t change too much).

  • There is no camera angle farther out than a medium-shot.

  • Intend on staying in the same location (remember paint is somewhat permanent).



Use a large green sheet

Chroma key backdrops/sheets are also available online:



  • Need a larger backdrop to ensure it doesn’t get cut off for any of the camera positions and angles

  • Need to be mobile with your set

  • Expect to see any of the ground below your actor (the edge between the wall and the floor will create a troublesome change in color and lighting)

  • Have a significant other that won’t let you paint a wall in the garage bright green

Manfrotto LL LB7626 Panoramic Background Cover - 4m, Chromakey Green


Build your own wall and paint it

Building your own wall and painting it enables you to:

  • If you have the time, the money, the tools, and some woodworking talent you can also build your own setup and then paint the entire thing. I won’t go into detail but if that interests you here is a link to a YouTube video.



The most common technique for up and coming filmmakers is the sheet. I like this option because it is cost effective and versatile, and the common issues with sheets are easy to solve:

– Wrinkles create shadows and shadows create post-production difficulty.

Solution: what else do you do with wrinkles? Ask your mom to iron your sheet (kidding. Give your mom a break for once…).

– If the sheet falls to the floor and then turns abruptly you will have the same problem as if you just paint the wall and the ground green: the bottom edge.

Solution: buy a long enough sheet that you can pull out the bottom edge to create a smooth curved surface from ground to wall.

– Too much green on the set will reflect green onto your actors, blurring the distinction between actor and backdrop. This is called “green spill” and it makes post-production frustrating at best, impossible at worst.

Solution: use the least amount necessary to safely achieve your final vision and follow the guidelines for effective lighting (below). If you already have an entirely green room, consider using black sheets to cover up any green that is not necessary in the shot.

Lighting

Time and again when researching or talking about chroma keying, you will hear the same thing: it’s all about the lighting.

How to light a green screen While your exact lighting rig will vary depending on several factors, here’s a diagram of the basic set-up you want for optimal chroma screen lighting. Notice the subject and screen are being lit separately.


Check out these lighting kits:









Green Screen Lighting Setup Diagram • StudioBinder



But how do you go from nothing to our beautiful diagram above? That’s easy. This video shows how you can get the best green screen lighting setup in just four minutes. A few easy steps are all it takes.

How to Light a Green Screen in 4 Minutes

Set up the green screen equipment Whether you have a cheap green screen lighting kit or something that rivals most blockbusters, you want to get that situated first. You should smooth out the material if you have a fabric or paper green screen. A good rule of thumb is to avoid any reflective materials in the shot. Jewelry and glasses can complicate this. If you know you need a green screen for a given shot, then you should keep tabs of what props are necessary and adjust as needed. Get the same lights As you can see from the diagram, you want two lights directed right at the green screen. Ultimately, it doesn’t matter a great deal what specific lights you get. You just want to make sure they’re exactly the same. Different lights have varying color temperatures. This leads to an uneven color balance.

Light the subject first After you acquire all of your green screen lighting, you may be ready to get that perfect shade. But before you focus on the green screen itself, you want to make sure the subjects of the shot are properly lit. In general, your subject should be about eight feet away from the green screen. To light them, you’re going to need the following lights.

  • Key light: The key light is the predominant light source for the subject. It should match wherever the light source (i.e. the sun, other lights in a building) would naturally be.

  • Back light: The back light creates a soft halo effect in the subject’s hair. Mostly used when the subject should be in a studio setting.

  • Fill light: The fill light creates ambiance within the scene and helps soften shadows created by the key light.

You may need to adjust the setup from our diagram slightly. For example, you may need more fill lights depending on the kind of shot you want. That’s okay! But that’s why you need to deal with the subject first. If you light the green screen first, then you may need to change it later based off what your subject needs to do. Then you’ve wasted a bunch of time for nothing.

Light the green screen Once you have your subject the way you want them, it’s time to position the lights to target the green screen. Each light should be the same distance away and at the same angle. This is the best way to ensure an even lighting across. You'll notice in these two diagrams that Setup #1 (left) will cast shadows from the subject, while Setup #2 (right) keeps the shadows outside the camera's field of view.


How to Light a Green Screen With Two Lights



While you can play with different angles, it’s generally a good idea to keep your two green screen lights in a similar position to the right-hand image above. That way the camera doesn’t capture any shadow behind the subject. The shadows instead appear off to the side, away from the camera’s view. All you’re left with is solid green, which is why it’s typically the best lighting for the chroma key later. Expose the green screen correctly Finally, you want to examine your camera monitor for the exposure. This is how much light your camera takes in. You want a little less brightness than normal so that you don’t capture colors outside of green. It’s also a good idea to lower your camera’s ISO setting. Sometimes, random specks of color appear in your shot, but you reduce this by lowering the ISO. But make sure not to lower the ISO too much as this can underexpose the green screen and lead to other problems. Once you adjust your camera, you may find you need to alter a few lights. Go ahead and do that as it saves you a ton of hassle later. Once everything looks good and you have an even green shade across the screen, you’re ready to start filming.


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