Chapter 12: keying and compositing, Keying, Keying overview – Apple Final Cut Pro X (10.0.9) User Manual
Page 334: Use chroma keys, 334 keying 334, Keying and compositing
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Keying
Keying overview
There are times when you need to combine two clips to create an image with bits of both. A
common way to combine two clips is to use a keying process, where the video of the top, or
foreground, clip is processed to eliminate either a color or luma value in areas of the video and
then is combined with the bottom, or background, clip.
For example, keying allows you to take a video clip of a person standing in front of a green
background and replace that green with a street scene, making it appear as though that person
is standing on the street.
This type of keying is accomplished using one of two keyer effects in Final Cut Pro:
•
Keyer: This general purpose chroma-keying effect is optimized for blue- or green-screen keying
but can key any range of color you choose. See
on page 334.
•
Luma Keyer: This is designed to generate mattes based on the image’s lightness—you choose
to remove the white or black areas and whether or not the gray areas should be partially
transparent. See
on page 343.
In addition to these keying effects, you may need to use a matte, a positioning effect, and color
correction to ensure the foreground video looks natural when keyed over the background. For
more information, see
on page 348.
Another way to combine two clips is for the foreground clip to have an alpha or matte
channel that defines which parts of the foreground clip to keep and which to replace with the
background clip. This is common when working with computer-generated logos or animated
graphics. For more information, see
on page 351.
Use chroma keys
A challenging part of creating a good chroma key is shooting the chroma key video, and in
particular, using a good, well-lit background that provides a uniform color to remove. A wide
variety of specialized chroma key background options are available, from chroma key paint
that includes highly reflective additives to chroma key cloth or paper sheets. Additionally, it is
important to use the best camera you can access and avoid using a highly compressed video
format such as DV or MPEG-2.
Keying and compositing
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