Graphics Reference
In-Depth Information
Control
Source tape
Monitor
Digital image store/
Processor
Source tape
Output tape
FIGURE 1.9
On-line nonlinear editing system.
Frames
Bird Sequence
Video 1
Dissolve
Transition
Plane Sequence
Video 2
Fade to White
Effect
Audio 1
Night Sounds
Narration
Audio 2
FIGURE 1.10
Simplified example of a time line used for nonlinear digital editing.
After a sequence has been digitized, an icon representing it can be dragged onto a time line provided
by the editing system. Sequences can be placed relative to one another; they can be repeated, cut short,
overlapped with other sequences, combined with transition effects, and mixed with other effects.
A simplified example of such a time line is shown in
Figure 1.10
.
The positioning of the elements in the time line is conceptual only; typically the data in the digital
image store is not actually copied or moved. The output sequence can be played back in real time if the
disk random access and graphics display are fast enough to fetch and compile the separate tracks on the
fly. In the case of overlapping sequences with transitions, the digital store must support the access of
multiple tracks simultaneously so a transition can be constructed on the fly or the transition sequence
needs to be precomputed (sometimes referred to as
rendering
) and explicitly stored for access during
playback. When the sequence is finalized it can be assembled and stored digitally or recorded on video.
Whatever the case, the flexibility of this approach, with the ability to change edits and try alternatives
without generational degradation, makes nonlinear digital editing systems very powerful.
1.4.3
Digital video
As the cost of computer memory decreases and processor speeds increase, the capture, compression,
storage, and playback of digital video have become more prevalent [
42
]
[
46
]
. This has several impor-
tant ramifications. First, desktop animation has become inexpensive enough to be within the reach of
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