Editing in Timeline mode 103
Once in your project, you can also stretch your mask to fit using Stretch from
the Fit drop-down menu on the Timeline context toolbar. Alternatively, you can
always adjust size and position using a transform adjustment (see p. 37).
Blue/green screening (Chroma Key)
This process, referred to as Chroma Key in MoviePlus, enjoys a few other names
including colour keying, matting, and colour separation overlay. It is a method
of removing a colour (or a colour range) from one video or image to reveal
another video or image behind it. The "removed" colour becomes transparent.
This process is commonly used for weather broadcasts and of course in many
movie blockbusters. To start with, the foreground subject—a weather presenter
for instance—is filmed against a solid-coloured and evenly-illuminated
backdrop. Using MoviePlus (or expensive studio wizardry in the case of live TV
weather slots), the solid coloured region of this video can be made transparent
using a Chroma Key effect, revealing an underlying video. In the case of some
weather presenting, the video "behind" the presenter can show a weather map
with animated symbols or weather systems. In movies, the process saves actors
being put in dangerous positions, such as visually-stunning explosions, or in
places that cannot be reached for practical or budgetary reasons, such as across
the other side of the globe or in space.
It's not only a background that can be removed; you can, for instance, hold up a
solid-coloured card while being filmed and later remove that solid colour from
the video to create a card-shaped cut-out. The alternate "background" video
would then display through this "hole".
