ADOBE PREMIERE PRO 2.0
User Guide
130
Each interlaced video frame consists of two
fields
. Each field contains half the number of horizontal lines in the
frame; the
upper field
(or
Field 1
) contains all of the odd-numbered lines, and the
lower field
(or
Field 2
) contains all
of the even-numbered lines. An interlaced video monitor displays each frame by first drawing all of the lines in one
field and then drawing all of the lines in the other field.
Field order
specifies which field is drawn first. In NTSC video,
new fields are drawn to the screen approximately 60 times per second, which corresponds to a frame rate of approx-
imately 30 frames per second.
Interlaced scanning of interlaced video fields compared with progressive scanning of a noninterlaced video frame.
A.
For interlaced video, first, the entire upper field is drawn to the screen, from top to bottom, in one pass.
B.
Next, the entire lower field is
drawn to the screen, from top to bottom, in one pass.
C.
For noninterlaced video, the entire frame is drawn to the screen, from top to bottom,
in one pass.
Most broadcast video is interlaced, though emerging high-definition television standards have interlaced and nonin-
terlaced variants.
Noninterlaced video frames are not separated into fields. A
progressive-scan
monitor will display a noninterlaced
video frame by drawing all of the horizontal lines, from top to bottom, in one pass. Computer monitors are almost
all progressive-scan monitors, and most video displayed on computer monitors is noninterlaced.
The terms
progressive
and
noninterlaced
are thus closely related and are often used interchangeably, but
progressive
refers to the recording or drawing of the scan lines by a camera or monitor, whereas
noninterlaced
refers to the fact
that the video data itself is not separated into fields. For example, it is possible with some modern cameras to use
progressive scanning to record two simultaneous fields per frame of interlaced video.
To create interlaced or non-interlaced clips
Ordinarily, interlaced fields aren’t apparent to a viewer. Because each field captures the subject at a slightly different
moment in time, playing a clip in slow-motion, creating a freeze frame, or exporting a frame as a still image makes
the two fields discernible. In these circumstances, it’s usually preferable to
deinterlace
the image—that is, eliminate
one field and create the missing field either by duplicating or interpolating the lines of the remaining field.
A
B
C