What is a green screen and how does it work?

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In today’s post, I’ll take you through some of the basics of what a green screen is, how-to DIY one, and how it can help you in your videos.

A green screen is what allows those amazing effects and locations in feature films, and sometimes photographs as well. The technical term for it is chroma key compositing, or simply chroma keying. We’re going to take you through what it is, how to use it effectively, and even give you a few tips on how to make one yourself at home!

What is a Green Screen?

It is a single-colour backdrop that allows filmmakers to superimpose one shot over the other. This means that if you want to shoot a video that looks like it is on the top of a snow-covered mountain, you don’t necessarily have to risk your actors and crew getting frostbite or hypothermia. Take your shots of the mountain separately, construct the bits you need in a studio in front of a green screen, and simply superimpose the two shots to get your perfect on-location shot!

What is a green screen

It is worth noting that it may be called a green screen colloquially, it doesn’t have to be green. It can be any colour that is not likely to be in the shot, and filmmakers are known to use a blue screen as well. The reason for the different colour is simple – if the shade of anything in the shot matches the colour of the screen, you risk that object being invisible.

For example, an actor wearing a bright green outfit in front of a green screen would appear as a floating head. To avoid this, you need to make sure that the screen colour is not used for anything in the foreground.

How does it work?

The green screen offers a ‘replacement’ colour, which your video editing software can key in on to replace with your chosen background. To reiterate our last point – the computer and software cannot distinguish between the green of the background screen and something in the foreground, so contrasting colour for the foreground objects cannot be stressed enough.

As long as the colour of the backdrop is consistent, it will allow the replacement/background shot to be seen effectively in the composite shot. This is why fabric is preferred to a textured wall or painted panels, and even then the fabric needs to be stretched out so that it does not create shadows.

How can I use a green screen effectively?

You can use it to put your actors in exotic locales for your budget film, or you can simply use your PowerPoint presentation itself as a backdrop over a zoom call while you make a presentation, the way weathermen do on the news.

What you need is a computer that has reasonable processing power to handle video, a video editing software that can take advantage of that green screen, and something that can record video in a format that will allow the software to edit your video.

For shooting, something as simple as an iPhone will do, and this can extend to other mobile phones, action cameras – just make sure the format they shoot in is compatible with your video editing software. Always mount the camera when shooting, and try to keep it as stable as possible, else you risk shake in one of the two video components, which will make the finished product look odd.

For editing, even free software like iMovie and Windows Movie Maker can take advantage of green screens. If you’re willing to shell out a little dough, you can opt for apps like Wondershare Filmora X, Adobe Premiere Elements 2020, or Cyberlink PowerDirector Ultra. Quite a few of these apps have trials versions that allow you use a full-featured version for a limited time, so you can try out your green screen skills before putting your money where your chroma keying is.

Can I make a green screen myself?

Sure you can! All you need is bright green (or blue!) bolt of cloth that is crease-resistant, and a way to pin it up as a background to the set which you intend to shoot at. If you’re shooting a film where actors are walking around or just a full-length shot of them, make sure that you extend the green all the way to beyond their feet.

That is not to say you can’t make a green screen out of other materials – you can make it out of green paper, or even painting the backdrop with bright green paint!

Green screens for personal use are also available online at reasonable prices. These range from small foldable screens that will form a backdrop for a single seated person, like a newscaster, to larger ones that are packaged with stands so that you can take a full-length shot of the subject. They are usually made of crease-resistant fabric.

What do I need to watch out for when using a green screen?

  • The lighting should be even across the backdrop. If the light is uneven, you risk the editing software not recognising some part of it and ignoring it during the processing phase. This is also why the backdrop cloth making up the green screen needs to be free of creases or folds, as those will create shadows.
  • Remember to light your background screen first, then whatever it is that you want to shoot. Softboxes are your friend when it comes to lighting, the diffused lighting helps reduce contrast and shadows. Arrange your lighting such that it minimises shadows thrown by the subject onto the screen.
  • Keep your subject sufficiently far away from the backdrop so that it remains out of focus. A minimum of 6 to 8 feet is sufficient distance for most purposes. This will also help reduce harsh shadows from the subject on the backdrop.
What is a green screen
  • The right angles between wall and floor become a hurdle because of the shadows they create, and using a cloth that you can make curve where the wall meets the floor, to form what is known as a ‘cove’, will help eliminate this problem. Remember, it needs to go all the way under the actors’ feet for it to be effective.
  • Try not to move the camera, the shake will be noticeable. Always use a tripod for this. In the same vein, do not change your camera angle during your shot, when you see it done in big-budget films, it is because they have an army of VFX technicians to make the result look right.
  • Never zoom in on or out of your subject. This will only make the subject appear larger or smaller while the background stays the same, a most disconcerting effect for the viewer.
  • Use a screen that will cover all the background behind the subject in the shot, and keep some room for error. If the subject moves outside the borders of the green screen, those parts will not have the intended backdrop in the composite scene.
  • Make sure that the two shots that make up your composite have near-identical colour balance, or white balance, else they will look like those old 70s-era movies that so obviously were shot at a different time in front of a green screen!
  • Finally, keep looking out for tips on how to improve your green screen skills – for example, making the background slightly out of focus for images lends a much more realistic touch to the composite images. For video, making sure that the subject lighting is similar to the shot of the background scene will lend it that much more credibility in the final composite scene.

With the computing technology and apps available to us today, using a green screen effectively can be something as simple as dropping in a scene background from Shutterstock to make your video more exciting. All you need to do is learn to shoot with a green screen effectively first.




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