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Lighting Greenscreens

Many editing software programs now have easy-to-execute chromakey effects, but, to get your scene looking good, you need to plan first and light it right. You have the greenscreen, the right editing software, and a great idea... but how do you make your subject look real?

Many editing software programs now have easy-to-execute chromakey effects, but, to get your scene looking good, you need to plan first and light it right.

You have the greenscreen, you have the right editing software, you have a great idea... but how do you make your subject look real? It all comes down to lighting. Lighting for greenscreens takes a lot of planning, a good eye for detail and pure imagination. In this column, we will look at the techniques and setups you can use to create believable greenscreen scenes. So... let's venture into the studio or your living room, if that is where you wish to work - away from the drifting snow or frigid temperatures that may surround you this time of year.

Lighting the Greenscreen

There are two major areas of concern when lighting for greenscreen: the background and the subject. The best way to approach greenscreen lighting is to treat each as a separate lighting setup. Let's take a look at lighting the green background first.

Did you ever wonder why video uses greenscreens to create special effects? Chromakey green - as the true greenscreen color is officially called, is a color that hopefully you will never see anyone wearing. OK, yes, some of your golf outfits may have this color emblazoned throughout, but usually the color is not part of our everyday fashion. It is also a color that no living being has as an eye color, something that can be a problem with the bluescreens that are used in film. Chromakey green is also a color that you can easily remove electronically from the image as a chromakey. Easy, yes, but to do so, you have to make sure the chromakey green background has no wrinkles or seams and is well lit.

Lighting the chromakey green background is actually quite easy. The first thing you do is determine the size of the background needed. This will help determine the area you need to light. If you are doing a simple one-person interview from the waist up, then your background doesn't need to be very big. There is no reason to light a 12-foot background if you are using only a five-foot space. Once you have determined the size of the area needed, set up two lights, one on each side of the background - just out of the camera shot. These lights should be diffused, so that their beams provide a very even spread of light over the area. You can use gels to diffuse the beams. Make sure the light is as equal as possible everywhere. The whole idea is to provide a solid, consistently-lit background that will reflect one color back to the camera. The more consistent the lighting and color, the easier it is to remove that color so that you can key your subject over a different background.

Lighting the Subject

Once you have lit your background, it is time to light the subject. This is where the planning and imagination really come into play.

Planning is essential for greenscreen lighting success. You have to determine a number of things before you even begin planning your lighting setup. When shooting or collecting the background footage you are planning to use, carefully study the lighting. Where is the main light source? What kind of light is it? Is it hard or soft? Indoor or outdoor? Bright or dim? Moving or steady?

You also need to determine the movement required in the scene, if any, as well as the size of the chroma-key green background. It is essential that the background be large enough to fill the scene. You also have to have enough space in front of the greenscreen to reduce any reflected green falling on your talent and your talent's shadow falling on the greenscreen. You want to try to get your subjects as far away as possible to make it easier to light them, as well as to prevent green reflecting on their skin and hair.

Setup One - The Ski Slope

Let's say you want to see your subject standing in front of a beautiful mountainous ski slope. The sun is bright, the sky is blue and the air is crisp. You send your crew out to get the shot for the background, because you know you don't want your talent to stand freezing on the ski slopes trying to get their lines right for the scene. In the studio, you will also not have to worry about skiers running in front of the camera, wind noise on the microphone and the sun changing as you do multiple takes.

Look at the footage. Where is the sun? How long are the shadows? If you did your planning well, you would have placed the sun in the shot so that it would naturally be coming in from a lower angle at about 4 o'clock on your talent's face (early morning and late afternoon are great times to use low-angle lighting). This would provide a very pleasing key light. The reflection off the snow on the slopes would provide the backlight and fill. Now all you have to do is duplicate that situation.

The sun is a hard light - therefore you would use a small, intense reflector spot located at the same angle as that of the actual sun when the crew took the shot. The fill light and the back light can both be softer, because they are created in the real scene by light being reflected everywhere by the sun off the snow. Place your backlight as close to the center of the subject as you can at the 12 o'clock position, so that it not only provides a soft light along the shoulders and hair of your subject, but it also eliminates any green that may be reflecting from the chromakey green background. It is essential that you can see no green on the subject. Then focus your fill light from the side opposite the key - at around the 8 o'clock position. Gel all of your lights with color temperature blue gels to duplicate the light from outside, and white balance as if you were shooting outdoors. The outcome should be pretty realistic, and your audience will never know the talent is warm and dry in a cozy studio (see Figure 1).

If you have purchased background footage, use the shadows to determine the placement of the lighting. Then go through the same procedure, duplicating what nature has provided.

Setup Two - Exotic Interior

What if your location is an exotic interior? You were able to get the rights to footage shot in an elaborate and ancient cathedral, and you want to show your talent having a hushed conversation in the massive space. To be believable, good lighting is the key.

For this shot, you will need a larger chromakey green background. Light it as evenly as possible. Then begin your lighting setup for the talent.

Carefully look at the footage you will use in the background. Where do the shadows fall? What kind of light is prevalent in the scene?

For the purposes of this setup, let's assume the lighting is diffused from a number of different sources, very warm and not really bright.

Set up a soft light as your key at the 4 o'clock position, so that it fills your talent's face. If you are working with two people having a conversation, decide which is the more important, and put that person on the side where more light will fall. The key light for one then becomes the fill for the other and vice versa. Set your fill so it is less intense than the key and doesn't give much direction. It should look like ambient spill light and match that in the cathedral. Finally, add a backlight at the 12 o'clock position, hanging above the actors if at all possible. Make sure you flag the backlight from your camera lens to eliminate lens flare.

When you have all of the lights set, white balance against a pale blue cloth. This will tell your camera that light blue is white, and the result will be a very warm-toned image. The result should be very believable (see Figure 2).

The Keys to Chromakey

To make your chromakey experience successful, remember that you must light the background greenscreen as evenly as possible, and you should place the talent as far from the greenscreen as the scene will allow. You need to carefully study the background footage to determine the type of lighting needed and then work hard to duplicate its intensity and type. From outer space to the dark ages, the sky's the limit. With good planning and careful placement of lights and talent, your scene should be quite believable.

Contributing editor Robert G. Nulph, Ph.D., is an independent video/film producer/director and teaches video production courses at the college level.

Side Bar: why go green?

With today's editing software, you have the ability to place any color behind your talent to use for a chromakey. All you have to do is make sure there is absolutely nothing close to that color in the clothing or eyes of your talent. The industry uses chromakey green because you so rarely see it in nature and fashion. You can buy chromakey paint or chromakey drops at your video supply store or big box retailer.

Tags:  January 2009
Robert G.
Nulph, Ph.D.
Thu, 01/01/2009 - 12:00am

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