How Compositing Works

For Class #7

 Instructor: Norman Hollyn

  T.A.: Denise McCarthy

 Messages: 310-490-7658

 Phone: 323/661-2704

 E-Mail: class@norman-hollyn.com  

 

Compositing Images Using Blue or Green Screen

We will discuss the compositing process in more detail in class, using these images as examples.

Images courtesy of HowStuffWorks


The original photography is an actress shot against a blue screen. The choice between blue and green is up to the d.p. and is dependent on what the surrounding material is. In this case, since the actress was shot in the studio, there is no surrounding material to worry about.

In this case, the background plate is a painting. It could be a still photo, a moving image (think of the scenery outside a car), or another live action shot.

A Black Core Matte is "pulled" from the foreground photography. The better the photography the cleaner the matte will be.

A White Core Matte is pulled from the Black Core Matte.

The Black Core Matte is exposed with the background footage, leaving a hole in which we will place the actress.

The White Core Matte is exposed with the foreground footage, losing all of the image that was originally the green color (or blue, depending on what screen color was chosen)

The two images are composited into one. Note that an actual compositie shoot takes into account image sizes and lighting, unlike this example. This would make the actress blend in better to the image. Note also the outline around the actress' shoes and body. This comes from bad lighting, which causes the green color to spill onto her body.

The images below show the difference between a static matte and a moving matte. The actors are moving but the rest of the camera image is locked off. The two areas can be handled differently. Since it is always cheaper to deal with a lock-off, as much of the frame is handled that way as possible.

The actors will be moving against the area that will be replaced by the model, shot in a studio. The only area that needs to be green screened is the area where they will walk past the image to be replaced. Note that blue screen would not work here, because too much of the photography is blue.

The composited image.

Images © 2000 by HowStuffWorks



All material not attributed to someone else is ©2000 by Norman Hollyn. Questions? Comments? Suggestions? Send me an e-mail at class@norman-hollyn.com
Last update - October 16, 2001