Green screens are everywhere in filmmaking. They’re arguably the most-used visual effect in storytelling outside of credits or title sequences, and they can open up infinite options for your project. But you’ve got to be able to use them correctly to get the best results and minimize the amount of time and money spent adding VFX to your film.
We won’t get into the history* of the green/blue-screen technique or what’s going on within the camera and why it works, but this blue/green technique is called “chroma keying” (using black/white is “luminance keying” or “luma keying”). Essentially, you’re choosing a color for your background (or foreground, screen, or body part) that is completely different from anything and everything else in your frame (usually green), isolating it, then making it transparent.
*Note: If you’re interested in learning the history of green/blue-screen techniques, check out this incredibly fascinating video by FilmmakerIQ.
There are many options for green screens, so research to see what’s best for you and your budget. You may not need a huge screen if you’re shooting a stationary subject, nor should you get a small screen if you’re shooting an action scene with a lot of movement.
If you’re planning on shooting in the same place for every project, it may be best to just buy green-screen paint and paint your background wall, which is what many production houses and movie studios do. If you’ve already got a couple of light stands or c-stands, it may be easiest to buy a piece of green fabric and clamp it between them.
The bottom line is, think about your projects and buy a screen accordingly. (On a personal note, make sure you buy a quality screen, because many times you get what you pay for).
Lighting Is Everything
If the screen is No. 1 on your equipment list, lighting is No. 1a. You MUST have even light (or as close to even as you can get) on your green screen to make the whole thing work. This lighting could either be from natural light or studio lights, but the first rule of chroma keying is making sure the key is the same color throughout, to make your post-production much more streamlined. Here’s a basic breakdown for getting dialed in on lighting the screen:
Check for Imperfections
Make sure there are no wrinkles, scuffs, tears, or stains on your screen, to avoid any shadows that can throw off your keying. Remove them by ironing, steaming, or letting the screen hang vertically for a few hours. (If you’re using paint, just make sure you clean or re-paint any scuffed or chipped areas.)
Position the Lights
Two lights of equal wattage should be positioned 15 degrees from the green screen on each side, pointing toward the screen. This is very important. Each light should be far enough away to light the entire screen to create an even color.
Check for Evenness
As I mentioned earlier, even lighting is crucial. Move your lights around to the best position to get the most even lighting on the screen; it will make your life much easier in post.
Light It Up
Be consistent and stick with one type of light, whether it’s LEDs, fluorescents, or tungstens. LEDs use less power and don’t get nearly as hot, but they are also much more expensive. Fluorescents are cooler in color temperature and actual temperature. Tungstens are cheaper, but use more power and get hotter to the touch.
Check for Zebras
If your camera has zebra bars, use them and slowly adjust the iris to identify hot spots on the screen. When you start to see the zebras, you know you’re overexposed.
Now that you’ve got your screen lit, you need to light your subject. The most important thing to know here is that you have to light your screen and your subject separately. The more separation you can have between them, the better your end result will be. With proper separation, you won’t have to worry about shadows as much, and you’ll minimize the amount of green reflecting or spilling from the screen onto your subject. If you don’t have a ton of space, however, you need to get more creative with your lighting and move the subject’s lights outward, so that the shadows are cast out of frame. Here’s a basic breakdown for lighting your subject:
- Turn Down the Lights: Turn off your screen lights so they won’t interfere with your subject’s lighting.
- Position the Subject: Keeping your subjects in the frame, position them as far away from the screen as possible, to give them some separation. This will also ensure the two green-screen lights aren’t hitting the subject. Have your subjects practice to make sure their whole body stays within the green screen.
- Use Basic Three-Point Lighting: A key light should be positioned about 15 degrees to one side of center and raised 3-4 feet taller than the subject, mimicking sunlight. A weaker “fill” light should be placed on the opposite side of the subject, and backlight will be your third light (positioned behind and to the side of your subject), providing a “rim” light around your subject. This will help further separate your subject from the background.
- Light It Up, Part 2: This works the same as with the screen. Choose a consistent type of lighting you want on your subject and use it only for your subject.
- Minimize Spillage: If your actors are standing on part of the green screen, have them stand on a different colored mat to prevent green light from reflecting onto them from below. If you’re still getting green spilling, reposition your lights or move the subject further away from the screen.
Those are the basics for a standard lighting setup, but there are times when you may need to match a certain scene, mood, or lighting arrangement based on your background. Think of how much different sunrise looks from mid-day, or the variance between an office building’s light and a candle-lit church. These are the best ways to light for a mood:
- Mimic the Natural Light: If the background for the green screen is an outdoor scene, keep in mind the direction of the natural light. For example, if your scene takes place at sunset, make sure the direction of the lights on your subject are positioned at the same angle as the sun. Also keep in mind the color temperature, as it will vary along with the time of day. Indoor scenes are very different from outdoor scenes as well.
- Use Gels: Match the color tone and temperature of your backplate by covering your lights with gels. If it’s a sunset, use warm gels on your lights to mimic the actual light in the scene. If you’re set in a winter environment or a doctor’s office, use cool gels on your lights, and so on.
- Refer to the Background: Whatever your background image/video is going to be, make sure you use images of it for reference. Having a visual aid will make it that much easier to light for the background scene at the time of shooting, instead of having to re-shoot for consistency.
Okay, your lighting is set! There are a few more things to consider, specifically for your subject, and then you can start shooting:
- No Green Clothes: Make sure your talent isn’t wearing anything green, teal, aqua, seafoam green, forest, or any color close to the color of your backdrop. The same goes for anything blue on a blue screen.
- Put on Some Makeup: Makeup is necessary for green-screen shooting, unless you’re filming a Dawn of the Dead sequel.
- But No Shimmery Makeup: Avoid using shiny lip gloss, eyeshadow, or blush on your talent. The lights will reflect off of this makeup and mess up your key.
- Look for Flyaways: Use a shine spray to get rid of fine hairs that are sticking up. This will make it easier for keying.
What to do next?
Basically, if you‘re happy with the result even without further edits, you can go ahead and upload your green screen footage or photo straight to Pond5. You can also process the image with chroma keying tools in your editing software and export your media as alpha channel or alpha matte. Alpha channel is very easy to recognize – it contains its well-known checked background which indicates that it‘s a transparent background. Alpha matte on the other hand contains the original footage and the black and white mask. You can upload both types of alphas. Here are the examples of alpha channel and alpha matte footage:
Alpha Matte Video: Time-Lapse Of Opening Blushing Akito Rose In Rgb + Alpha Matte Format by zygistudio.