Green screen is a term used to describe the mixing of two images or frames to form one complete image. The most common scenario is the combining of a foreground element with a background image, such as 3DATS co-founder Brian Zajac conducting aMoreGreen screen is a term used to describe the mixing of two images or frames to form one complete image. The most common scenario is the combining of a foreground element with a background image, such as 3DATS co-founder Brian Zajac conducting a presentation in a virtual environment, made possible by being filmed behind a colored desk and in front of a colored screen.
The colored environment is then removed, isolating the presenter who is then composited with a virtual studio created with 3ds Max. A number of other terms are used to describe this technique, including blue screen, keying, and the color difference system, but another term used more commonly throughout the CG industry, and one we will focus on in this chapter, is the term Chroma Key.Even though the chroma key technique is relatively quick and simple to execute, there are a number of guidelines that you should bear in mind when producing this type of work.
We have known endless hours to be wasted in the studio hand painting or animating mattes dealing with poorly shot scenes. We will provide a short overview on the history of the technique and then explain some proven methods for shooting a chroma key scene.
Many books have been written about chroma key on several different levels, going into the highly technical ways that the computer calculates the matte generation and all the other elements of the chroma key software. In this chapter, we will try to cover the more essential parts of the keying process without adding information that most people will never need. The whole process of chroma keying can be used for many different areas of CG work, not architectural visualizations alone. All the information we provide is relevant to any end result you wish to create. This chapter is equally relevant for creating CGI stills and film sequences.
For stills work, chroma key can save valuable time painting a matte per subject, and, for film work, it is invaluable unless you have an excellent team of rotoscopers.