How to use a Green Screen

If you found this blog post, you either have an idea of what a green screen is or you are fully aware of the concept. Either way, we’re here to teach you a thing or two in the matter. 

Also, you can browse our blog in order to find more articles about filmmaking. We’ve covered a few topics such as how to make a storyboard, how to edit a great trailer, what is CGI, and so much more! But now, let’s focus on green screens, so let’s get going!

What is a green screen?

So first off, what is a green screen? Well, a green screen is a canvas that is placed in the background of a shot. Ironically, the screen itself doesn’t necessarily have to be green, nor has it always been green. But we’ll go through that later.

The effect applied to this green screen is actually called chroma keying, which will actually be applied in post-production. This has been used countless, many times throughout filmmaking and is well more present in modern films.

So what is chroma keying? 

As mentioned before, chroma-keying is a post-production process that layers one image on top of another, applied on top of the green canvas on the background of the shot itself. So what kind of background do SFX artists layer on top of the canvas? Well, anything ranging from explosions to computer-generated cities, spaceships, you name it, the possibilities are endless.

Green Screen effects don’t necessarily have to be used in every movie, in fact, in the majority of cases, using one is not required at all. In short, if you have to film a shot in the park, we suggest you just drive the mile and film your shots at the park in front of the trees and bushes.

However, if you can’t reach the wondrous elven city of Rivendell (for obvious reasons) a green screen effect is required.

Take a look at this picture and try to come up with an idea on how to deliver anything similar without the costs being too expensive or time-consuming.

Have you figured it out? Because I can’t think of anything else other than a green screen and applied CGI on top.

So now you may ask, “Hey, so what was actually being filmed in the studio?” well, the answer resembles something similar to this:

Why are Green Screens Green?

As mentioned before, not all green screens are exactly green, however, it is well known that the vast majority of them are.

“Why?” You may ask. The answer is simple.

When the desired shot is ready, CGI artists will proceed with the post-production process we mentioned earlier, chroma keying.

In this process, the highly saturated green tones are digitally replaced with the desired background image. 

These saturated green tones usually don’t belong anywhere near the colors of everyday scenes, they even stand out and generate a huge value contrast even when placed behind grass, trees and other natural green subjects.

Another argument to keep your background canvas green is the fact that human skin in all its varieties lacks the color green regarding the RBG spectrum, thus making it very easy to filter these tones out.

Below, we’ll show you an example of color picking on a real green screen (left) vs. color picking on a grass field with soft, warm sunlight. 

Bet you can feel the difference, huh?

This, however, does not mean you cannot work on a less saturated canvas. In fact, as long as your foreground is fairly distinguishable from the background you’re good to go!

How much is a Green Screen?

Well, this is a tough one. The truth is that it really depends. The cost of a green screen may vary between 35 and 175 USD and your best fit is proportional to the amount of use you’re giving to your screen.

Here are our best and most recommended picks, check them out!

EMART Green Screen 5×7 ft.  

This is one of our most recommended green screens, it’s simple, effective, and worth the price.

The fabric of the green screen itself is crafted with high-quality polyester fabric, which is less likely to wrinkle throughout its use.

On the side, It comes with heavy-duty spring clamps which firmly hold down the backdrop to the crossbar with pivot-table pads that perfectly adjust to any surface.

This is a perfect fit for filmmakers who have to carry their working tools around since it weighs less than 6 lbs and conveniently comes with high-quality nylon carrying case.

Lincostore AM243 

If you’re at a stage in your career in which you can afford to spend a few bucks, then this setup is definitively for you.

It comes with 2 24×24 inch, squared umbrella-style photo softbox with white square diffusers, which eliminate shadows and softens up light, and evenly illuminates the green screen with its own inner aluminized surface.

On the other hand, the umbrella is constructed with durable, top-quality, translucent white fabric, permitting light to pass and producing a soft light on your foreground, casting a similar light to a cloudy day would.

Besides, the nylon green screen makes for a durable green screen and a lifetime companion.

Tips for using a Green Screen

Last but not least, in case you already have your desired green screen and want to get the show on the road, here are some simple tricks to help you out on your first experience.

Uneven lighting kills your the chroma key process

As you already know, chroma-keying is the process in which you filter the background off and apply whatever image or video you have in mind. However, if the green screen is affected by multiple sources of light in uneven ways, filtering out will be way more tedious and less effective.

The main sources of uneven light are wrinkles, so for this, we suggest you fully stretch your green screen with clamps. In case you have a cloth or cotton green screen, you can iron or steam your green screen to remove these wrinkles.

Avoid Cast Shadows on the Screen

If you have a cast shadow on your screen, then the chances are your newly rendered CGI background will have the cast shadow of the actor too. Therefore, placing adequate lighting in front of the canvas is key. 

If you can still see shadows on your green screen, your subject might be too near the screen. So do consider filming your subject a few steps away from the canvas.

Don’t light your Green Screen to Heavily

Providing too much direct light on a green screen made out of reflective fabric will only result catastrophically, why?

Well, casting a heavy, direct light on your green screen will make the light bounce right back at the actor in front of the green screen. Resulting in reflections of green rim lighting on your subject.

This not only creates a weird green tone around the contour of your actor, but also complicates the chroma keying process, since your subject will consequently have some green hues. 

Filtering out the background will be a harder task since your actor won’t stand out from the green background.

This will not only result in more work for whoever is doing the post-production process, but the chances of the end results being messy too are quite high.

Increase your shutter speed to get rid of motion blur

We recommend you set up your shutter speed to at least 1/100, this is simple, the higher the shutter speed, the less motion blur your subject will have.

Now, why do we want to reduce motion blur? Simple, filtering out blurry green tones is no easy task, resulting 99% of the time (if you are lucky) in a messy end result.

I know motion blur effects might be crucial to reinforce your scene, but don’t worry, you can just add this in post-production later!

Match the lighting on your subject to that of the desired background image.

Last, but not least, avoid the mistake most filmmakers are guilty of, which is not matching up the lighting on your subject vs the lighting on the background.

Even if your subject is beautifully lit, you have to take into account the desired background image beforehand.

Let’s take this shot for example:

It is very easy to tell that the background wasn’t being taken into consideration the moment this shot was being filmed, why?

Easy question! If the directors had taken into account the way the background was lit beforehand, the lighting on the actor would be nothing similar to the one above.

Given that the background is lit with cooler blues and smokey effects, there’s no way the light hitting on the driver would turn out to be so radiant and red.

After some editing, here’s what we came with as a more believable result: 

Cooler and more diffused lights actually help the actor blend in with the scene in a more relaxed and believable fashion.

We hope this article helped you know a bit more about green screens and how it’s used. Remember that if you are looking for royalty free music for your projects, HookSounds offers different licenses that can adapt your needs. Why HookSounds? Just listen.