Chromakey Photography

Since digital cameras became mainstream with pros, there has been an increasing interest in Chromakey photography. Chromakey is the process of using a blue or green screen as a background and then removing that background (and replacing it with something else) in software, like our Primatte plugin for Photoshop.

However, I’m not going to discuss the software. The well kept ‘secret’ about Chromakey is that the whole process has more to do with the photography side of it than the software. You want to understand what the software is looking for and then set up your photo shoot to give you images that fit that bill. If everything is shot right, then it’s pretty easy once you get your images into the software. If not, then you potentially have some very green, and probably very angry, clients. A lot of the info out there that talks about avoiding green, angry clients is oriented towards video. So our goal here is to provide you with tips that apply specifically to Photography.

There are a few components that go into a good Chromakey photo shoot: Lighting, Subject Positioning, and the Background. There’s many different ways to combine these successfully as they all interact with each other. What ‘works’ will depend on your equipment, what the subject is, and the environment you’re shooting in. Since most photographers are using green screens, we’ll just refer to Chromakey as green screen. But it’s essentially the same thing regardless of whether your shooting a green or blue screen. Actually, any color will work as long as that color isn’t present in the foreground subject. For people, that means red, yellow (skin tones), black, and white are eliminated, leaving us with blue or green. Green is a less common clothing color so that color is usually preferred.

Like many things in photography, shooting green screen is as much art as science. There’s a learning curve and you definitely want to try your setup out before throwing clients in front of it.

Color Spill

Spill is the term that refers to: 1) color that reflects off the background or walls of the room to cast a noticeable tint on areas of the subject or 2) color that’s showing through semi-transparent areas of the subject, like hair or a wedding veil. The goal of your setup is to reduce Spill as much as possible, so that you don’t have to deal with it in software. If not dealt with when shooting, dealing with the spill can easily take longer than the photo shoot itself. It’s the main reason that people give up on green screen photography. However, if the shot is setup correctly, it’s mostly avoidable… you just need to be aware of it and make adjustments as necessary BEFORE you shoot.

Usually you see Spill on the back of the shoulders, side of the arms or legs, and through the hair.

Positioning

You want to get the subject as far away from the background as possible. This reduces the possibility that light reflecting off of the background will spill onto the subject. 6-10 ft. is ideal, and 4 ft is the minimum. It is possible to have a successful shoot with the subject closer than 4 ft, but other problems start being introduced, like shadows on the background or bright spill and you’re potentially setting yourself up for a lot of Photoshop work. I have seen situations where the subject was a couple feet away and it worked fine. In that case, the lights were above the subject pointing down, preventing any shadows to appear in the head/shoulder shot. This would probably not work with ¾ or full length.

If the walls or ceiling are close to the subject, it’s helpful to paint them black or hang black fabric on them. Light bounces all over the place and that light can turn your background into a big green or blue light. The black material helps soak up that light and avoids spill on the front of the subject, which can be especially problematic.

Lighting

There is no set rule for lighting. It really depends on how much room you have, what equipment you have, and what you’re shooting. For things like little league shots, two umbrellas in front of the subject work just fine, but produce somewhat flat lighting. For senior portraits, you might want to use a 3 light setup to create more moody or artistic lighting.

You have more flexibility if the subject is 6 - 10 ft away from the screen. Light from the background falls off after 5-6 ft, so you naturally end up with less spill. This also makes the foreground a bit darker than the subject which is helpful. You want the background to be about a ½ to full stop below the foreground. So if you’re only using two umbrellas, 5-6 feet is ideal.

You can light the background with separate lights if the background is too dark, as you don’t want the background blending into the shadow areas on the subject. However, you need to be careful about lighting it too much and increasing the amount of spill. If you do light the background, you should plan on having the subject further away. 8-10 feet would be more appropriate in this case.

There are some other lighting tricks that can be helpful. A hair or back light can give definition to the edges of the head. This can make it easier to separate the hair and reduces spill on the shoulders. However, if it’s too bright it can add a glow to the hair which looks fake when you remove the background.

You can use a light on the floor pointing upwards to help minimize spill on the legs and arms.

If you’re doing full length, you can use a floor light pointing down to help eliminate shadows on the floor. This will result in more light bouncing off of the green floor on to your subjects legs, so may or may not work out.

If you’re getting a lot of green spill on the shoulders and arms, it’s also possible to use a magenta back light. This is sort of a last resort. It can help, but it’s tricky to use, as you don’t want to give everything a magenta cast. Giving your subject magenta shoulders instead of green ones won’t help you out much.

Background

The background needs to be a flat, consistent color, but you want to achieve this with the least amount of light possible. You want to avoid turning the green screen into a big green light. However, if there’s a lot of variation in the color of the background, that will cause you problems so try and find that point where’s there just enough light on the background to keep a consistent shade. A little variation is ok, but having a bright hot spot in the center radiating out to a dark green on the edges will give you a lot of trouble.

Sometimes you’ll get this flat color naturally with the same lights you’re using for the subject. You can also light the background separately, but expect to have a little more spill. So moving the subject further away from the screen will be helpful in this case. Again, especially with green, you want to keep the background at about a stop below the foreground.

The color also matters. You want a blue or green that is as pure a medium tone blue or green and pretty saturated. Most software, like our Primatte Photoshop plugin, works with saturation, so having a screen that’s too light or dark will make things difficult.

Since you can’t always predict would people will wear, some photographers bring a blue and green screen to the shoot. If someone shows up wearing a green dress you can switch to the blue screen.

Also, for shoots where you know the subjects are primarily wearing white or black (e.g. wedding, formal, etc.), a blue screen may be a better choice. Blue color spill is more forgiving than green. Our eyes are used to seeing it because of fluorescent lights and shadows will sometimes have a bluish tint. So it doesn’t look as unnatural as green does and it’s not as critical to get rid of every last bit of spill.

In addition to proper lighting, the material the background is made of can have a huge effect. You don’t want to use something like polyester which can be very shiny. This causes a lot of the light to bounce off of the background, creating spill. Some papers, particularly Savage Paper’s Tech Green #46, work very well. Not all papers do, however. Felt-like materials work excellent and in particular we recommend a fabric made by Velcro. It’s inexpensive, the right color, wrinkle resistant (wrinkles make lighting tougher), and works beautifully. It’s a very soft, foam-backed fabric which diffuses the light and prevents it from bouncing off. It’s available from many places (chroma-key.com, filmtools.com).

In Closing

Ultimately you need to do some experimentation. As you can see there’s a lot of variables and it’s not always clear how they will come together. The more testing and experimentation you do the more confidence you can have that your shoot will key out easily in Photoshop (or wherever).

Not all of these tips and tricks will apply to everyone or every situation. They should help you find a good setup faster and give you some guidance on what to look for. Good luck with your green screen shoot and let us know if you have any problems or find some great tip that we haven’t listed here!

Happy Photoshopping...

Jim Tierney