Adobe AFTER EFFECTS 5.5 Help Manual page 41

Adobe After Effects Help
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In interlaced video, a frame is divided into two fields. Each field contains every other
horizontal line in the frame. A TV displays the first field of alternating lines over the entire
screen, and then displays the second field to fill in the alternating gaps left by the first
field. One NTSC video frame, displayed for approximately
interlaced fields, displayed for approximately
Interlaced video describes a frame with two passes of alternating scan lines.
In noninterlaced video, scan lines are drawn in order from top to bottom, in one pass.
Computer video and computer movie formats are generally noninterlaced. Motion-
picture film is similar to noninterlaced video because it also displays an entire frame in one
pass.
Interlacing is a factor in image quality only for certain effects, such as rotating a frame or
compositing video with digital effects. It is a characteristic of footage capture and display,
not a structural component of file formats or media. You can easily play back a digitized
NTSC or PAL movie (interlaced) on a computer display (noninterlaced), or display a 35mm
photograph (noninterlaced) on an NTSC or PAL video monitor (interlaced).
If you use interlaced video in a composition or want to use an After Effects movie in an
interlaced-video medium such as NTSC, you must separate fields as you import and field-
render the composition to a finished movie file. For more information, see "Using inter-
laced video in After Effects" on page 43 and "Testing the field-rendering order" on
page 302.
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Preparing and Importing Footage
/ of a second, contains two
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30
/ of a second each.
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60
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