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OPERATION
3.12.6 VCG Film number Pulldown Indicator (NTSC only)
Film is typically viewed at 24 frames per second (fps) while NTSC video is
viewed at 30 fps. To compensate for this difference in the frame rates,
telecines use a 2/3 pulldown. Since each video frame is composed of two
video fields, video is viewed at 60 fields per second. Telecines can transfer
24 film frames to 60 video fields (30 video frames). The resulting ratio is
24:60 or 2:5, which means 2 film frames every 5 video fields. The 2/3
implies that one of the film frames is transferred to 2 video fields, the
following film frame is transferred to 3 video fields, and so on.
A video frame is always composed of a field 1/field 2 sequence, and is
defined by a unique time code number. The film frames will not always be
in phase with the video frames. With the 2/3 pulldown, the film frames
alternate between being 2 video fields only and 3 video field long. The 2/3
sequence creates four types of picture frames, called A, B, C, and D.
Figure 3-15 shows the relationship between the time code, video and film
frames.
0
F i l m
B
V i d e o
B
0
B B
Figure 3-15: Film to Video Relationships
The 'A' frame is always a f1/f2 picture, the 'B' frame is a f1/f2/f1 picture, the
'C' frame is a f2/f1 picture, and the 'D' frame is a f2/f1/f2 picture.
During 24 frame per second transfers in NTSC, a pulldown indicator is
added to the right of the film frame numbers. This indicator shows whether
the transferred frame is A, B, C, or D type. An underscore (_) shows video
frames that contain two different film frames.
shown in the following table:
Indicator
A
B
B
C
D
D
Model 4025TR Film Footage Encoder Manual
1 / 2 4
1 / 1 2
C
B
B
C
C
D
1 / 3 0
1 / 1 5
B C
C D
Type of Frame Indicated
A Frame
B Frame first 2 video fields
B Frame third video field
C Frame
D Frame first video field
D Frame last 2 video fields
1 / 8
1 / 6
D
A
D
D
A
A
1 / 1 0
2 / 1 5
1 / 6
D D
A A
The indicators used are
Page 3-63
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