Hack 22. Shoot a Green Screen Image

Successfully shooting a green screen (or blue screen) requires attention to detail.

Creating a believable composite image requires you to capture a usable green screen image. Although most software applications are capable of dealing with poorly acquired footage, you shouldn't count on your application's ability. Simply put, if you shoot a bad green screen, don't be surprised if you wind up with a bad composite. Garbage in, garbage out.

For the purpose of this hack, green screen refers to any background that consists of a single, solid color, whether it's green, blue, or some other color you decide to use. When I refer to, green you can substitute whatever color you are using.

2.7.1. Locating a Green Screen

If you're lucky, you'll be able to find and rent a stage with a complete green screen cyclorama. A cyclorama is often referred to as a cyc (pronounced "syke"), so if you are going to call around for a stage, you should use that terminology. Most of us, however, aren't lucky enough to either live near a stage or afford one.

Fortunately, there are a number of methods you can use to create your own green screen. If you have a room or office you can use temporarily, you can assemble your own green screen using home-improvement supplies [Hack #14]. Or, if you don't mind something semipermanent, you can paint a wall a solid color, being careful to keep the color consistent across the wall. Finally, there is always the option of simply using a large section of green fabric and hanging it from a rod.

Many amateurs and professionals shop for green screen materials at Film Tools (http://shop.store.yahoo.com/cinemasupplies/) in Burbank, California. Film Tools carries a wide range of video- and film-related items, from director's chairs to video carts.

2.7.2. Lighting a Green Screen

The primary key to capturing a good green screen image is the lighting. If you light your green screen poorly, you'll spend time in post-production trying to fix it. Save yourself the headache and just do it right while you have the chance.

Your actors should not wear anything green. When you go to matte out the color green from your scene, you don't want to matte out portions of your actors! This same principal applies to your props, as well.

2.7.2.1. Lighting the background.

When lighting, concentrate on lighting the green screen first. This means you should not have any of your actors or props within the area of the green screen. You will want to light the green screen evenly, meaning you should light to remove any shadows, light or dark spots, or glare. You might also find it useful to use green gels over your lights to help even the hue across your green screen. Figure 2-14 shows a poorly lit green screen, opposed with a well-lit one. The goal is to have an even color across the screen.

Figure 2-14. A poorly lit green screen (left) and a well-lit one (right)

2.7.2.2. Lighting the subject.

Only after lighting your green screen should you bring in your actors and props. Light your subject just as you would normally, keeping in mind the background you intend to use in the composition. While lighting your subject, make sure no shadows are cast onto your green screen, and if they are, remove them (by adjusting or adding lighting).

Also be aware of any spill occurring from the green screen onto your subject. Spill refers to the reflection of green off of an object. You can remove spill by, yes, more lighting. So, if you notice a green hue coming off of your lead actor, attempt to reduce it by lighting your lead actor from behind. Additionally, gels can be helpful when trying to reduce the occurrence of spill, as they can counteract the reflection.

2.7.3. Shooting a Green Screen

Although shooting a green screen seems easy enough, I recommend practicing a few times before taking other people's time to shoot your scenes. There is a lot you can learn by recording just a prop in front of a green screen and then attempting to composite it onto a background. You might even want to practice on a smaller scale, just to get a feel for what it takes to light and composite a scene successfully.

When shooting, you should keep your camera in a static position. If you plan on having a moving background, it will be extremely difficult to match the camera movement to the movement of your background (if not impossible). Even if you're able to view your composite in real time, it will take a long time for you to get the camera movement to match the background in a believable manner.

I once worked with a director who insisted on using a moving background for a shot. Even though we were able to composite the green screen and background in real time, it took us 43 takes to get one shot that was somewhat usable in the final project. Unless it is truly needed for your story, stick with a static background and save yourself the headache.

If you have lit your green screen and your subject well, then actually recording the footage will be as easy as recording anything else. When you're finished and you go to composite your footage, it should be almost effortless. The less time you spend working with your composite, the more time you'll have to make it look believable by adding shadows [Hack #71] and editing your scene.