Adobe PREMIERE 5 User Manual page 351

ADOBE PREMIERE 5.0 343
User Guide
Television signals are interlaced because of problems with early television sets. The screen
phosphors displaying the image faded too quickly: When early televisions displayed a
picture using progressive scan, the picture was already dark at the top of the screen before
the last scan line was displayed. By addressing this problem, interlaced video became one of
the world's television standards. Even with current technology, interlaced video is still useful
because it can increase the perceived resolution of motion using less bandwidth than
progressive scan.
By the time computers began using video monitors, the problems with phosphor fading
and display rates had been solved, making progressive scan practical for computer monitors.
Motion-picture film, while not technically video, is similar to progressive scan because it
displays an entire frame at once.
Interlacing is a characteristic of capturing and displaying clips, not a structural component of
file formats or media. For example, it is possible to play back a digitized NTSC movie (inter-
laced) on a Mac OS or Windows monitor (progressive scan), or display a scanned 35mm film
frame (progressive scan) on an NTSC video monitor (interlaced). However, progressive-scan
video provides better final picture quality when editing with filters and effects that affect
motion, including rotating a frame or compositing live-action video with special effects.
In addition, thin lines and small text are more likely to flicker on an interlaced display. When
you diagnose problems related to interlaced fields, view the clips on an interlaced television
display, because diagnosing field problems on a progressive-scan monitor is unreliable.
If you plan to slow down or hold a frame in a clip, you may want to prevent flickering or visual
stuttering by deinterlacing its frames, which converts the interlaced fields into complete
frames. In the opposite case, if you're using progressive-scan source clips (such as motion-
picture film or computer animation) in a program intended for an interlaced medium such
as television, you can separate frames into fields using a process known as field rendering
so that motion and effects are properly interlaced. For information about deinterlacing,
see "Freezing a video frame" on page 166. Premiere can play back or export video as inter-
laced fields while maintaining quality. For information about modifying, playing back, or
exporting interlaced fields, see "Processing interlaced video fields" on page 162, "Keyframe
and rendering options" on page 64, and "Exporting video files" on page 304.