Green Screen or Blue Screen Shooting

Green screen or Blue screen shooting is done when you'd like to composite an image onto another image. It works by selecting a specific color or range of colors to make transparent, then placing either a still image or plate shot behind it. The main reason green is used is because green is the color that is furthest away from human flesh tones.

When doing any visual effects work the first thing that should be done is consult with the person doing visual effects and request that they be present. Because they ultimately have to work with the footage you shoot, it's important to shoot it as they recommend. Ultimately they are the ones with more experience.

Choosing Green Screen or Blue Screen

Which color you use to key depends mostly on what items or people you are shooting. If you are shooting a green car, a blue screen will be best. Ask what items will be shot so you can be sure that they will have no issues when they go to key it.

It may also be a good idea to shoot blue screen if you have a lot of highly reflective objects. Blue can appear to be more natural in reflections than a bright green, so this can save in cleanup when the image is brought into post.

With blue screen you can get away with reflections a little better, also you are adding yellow to get rid of blue, where as with green you are adding magenta. Yellow is a bit more pleasing color otherwise.

Chroma vs Digi

When ordering a green screen or blue screen, you can either order Chroma or Digi colored fabric. Chroma Green and Chroma Blue were designed for VFX shots when using negative film. The sheer “lime green” brightness of Digital Green and the “smurf” blueness of Digital Blue allows for a better color sampling and easier lighting all around. Chroma is not recommended unless you are shooting on film.

Lighting

The screen must be lit evenly. A light meter can be very handy to make sure you have lit the screen properly.

Blue is an inherently less bright color, because camera sensors, and human eyes are less attuned to it. Because of this blue keying requires almost a whole f-stop more light (twice as much light).

You can add green or blue to your lights that are lighting the screen to increase separation. If you are doing full body shots this may not be possible as the lights lighting the floor cannot be green as they will have to also light the person.

Knowing what will be composited behind them will dictate how you light your subject. Disect the image that is behind them and figure out how it is lit. You will want to match this lighting to pull off a convincing composite.

Camera

The highest possible color resolution should be used with the least compression. The highest resolution available should also be used. Questions about what the action is should be asked so you can determine if shooting vertically is a good idea to retain more resolution. If it's a full body shot with someone talking and minimal hand movement, vertical can be a good choice to maximize resolution. If the shot is a medium shot and the character moves their hands or makes wide gestures, horizontally may be a better idea.