Methods for Chroma Keying

Chroma keying refers to replacing a specific color key with another image. Normally, this is referred to as green screen or blue screen. Certain types of chroma keying are used every day, in particular, the weather reports. While the basics of the chroma key replacement are similar, there are a few different ways to go about achieving the chroma key effect. The process of chroma keying combines production and post production techniques.

Background

The background used when shooting the film is important for chroma key. Green and blue backgrounds are used, as these colors are very different from skin tones and colors. There are several different options for background. The best choice is the use of chroma key paint. This is special paint that was designed to be matte and not reflect light.

Unlike regular paint, chroma paint only contains one green shade while normal paint can have many different shades. This makes the color replacement difficult, as only one or two shades will be replaced. Chroma paint makes it easy to replace the 1 chroma key or color shade. Chroma paint can be applied to a cloth or backdrop if an entire room or studio is not available.

Lighting

The lighting when doing chroma keying is also critical. It is best to try to minimize any shadows, as this makes color replacement difficult. The lighting equipment can be one of the most expensive costs besides the camera. At the minimum, a foreground and backlight light will be needed. Ultimately, the more lights the better. It is also possible to use filters for other lighting effects. Try to light the entire area as much as possible. Also, try to minimize any shadows. Lighting the subjects from the back can be the best way to eliminate shadows.

Software

A good software package will make the postproduction of this effect easy. The most basics of this process involve removing the background chroma tone with another background. This will overlay the two pictures. The chroma key can be completely replaced, or the chroma key can be made completely transparent and then the second background will be seen through the transparent layer. A few of the very common editing programs that can easily do this effect include Adobe Premiere, Apple Final Cut Suite, Sony Vegas and Adobe Aftereffects.

It can be best to apply a matte or masked to the subject and then start to exclude the chosen color. There are many little tweaks that can be used including softening the edge of the subject and suppressing any colors. It is important to try to make the two composite pictures as seamlessly integrated as possible.

When to Use Chroma Keying

There are several circumstances in which green screen is particularly useful. Many times the budget may not stretch far enough to travel to locations around the world. Shooting the scene in front of a green screen and then compositing it in the scene with a location background can keep costs down. Also, scenes that may occur in environments that do not exist or are dangerous can easily be done with chroma keying. It is also possible to have the actor perform dangerous and impressive stunts in a much safer environment.