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linear editing Before digital video editing, programs were edited together by
copying shots from the original source tapes to a master tape, one by one. Because
the assembly was linear, any changes in duration made to an earlier point of the tape
required reassembling the movie from that point forward. See also nonlinear editing.
looping A playback mode in which clips and projects go back to the beginning
whenever the playhead reaches the end of the media. You can turn looping on or o
by clicking the Loop Playback button below the Viewer.
lower third A television industry term for a graphic placed in the lower area of the
screen, usually to convey details about subjects or products. A common use of lower
thirds is to identify individuals on the screen with their names and job titles.
luma A value describing the brightness of a video image. A luma channel is a
grayscale image showing the range of brightness across the whole clip.
luma key An eect used to key out pixels of a certain luma value (or a range of luma
values), creating a matte based on the brightest or darkest area of an image. Keying
out luma values works best when your clip has a large discrepancy in exposure
between the areas that you want to key out and the foreground images you want to
preserve, such as a white title on a black background. See also chroma key, matte.
Mail Mail is the email program that comes with Mac OS X.
markers Markers ag a specic location in a clip with editing notes or other
descriptive information. You can also use markers for task management. Markers are
classied as standard informational markers (blue), to-do items (red), and completed
to-do items (green).
mask An image or clip used to dene areas of transparency in another clip. Similar
to an alpha channel. The color correction tools can create masks based on a color you
choose or a shape you create. See also alpha channel.
matte Sometimes referred to as a holdout matte. An eect that uses information in
one layer of video to aect another layer. Mattes are useful when you want to use
one clip to selectively hide or reveal part of another; for example, you could use a
round spotlight shape to reveal parts of a video layer. Matte eects can be used by
themselves to mask out areas of a clip or to create alpha channel information for a clip
in order to make a transparent border around the clip that can be composited against
other layers. See also alpha channel, compositing.
media A generic term for elements such as movies, sounds, and pictures.
544 Chapter 18 Glossary