Matrox Electronic Systems Matrox RT.X2 - Manual (Page 180)

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Appendix A, Understanding Standard and Advanced Pulldown
Overview
Part of your project’s workflow may involve the application of a pulldown
technique to convert your input video to your project’s video format. Pulldown
can also be applied to your output video to meet certain requirements. When a
pulldown is required in your project, Matrox RT.X2 performs either a standard
2:3 pulldown or an advanced 2:3:3:2 pulldown.
Standard 2:3 pulldown
Standard 2:3 pulldown is often used as part of the telecine process to transfer
24 fps film footage to 29.97 fps interlaced video. This pulldown method is also
used to convert any 23.98 fps progressive video to 29.97 fps interlaced video,
such as for converting 486p @ 23.98 fps video to NTSC.
In order to convert 24 fps film or 23.98 progressive video to 29.97 fps interlaced
video, additional video frames, and more specifically video fields, must be
created and added to the video sequence. For example, to convert a sequence of
four film or progressive frames, five frames of video are needed for a total of 10
video fields. Therefore, one additional video frame or two video fields must be
created. To accomplish this, the first and third frames of a four-frame film or
progressive video sequence are each converted to two video fields. The second
and fourth frames of the sequence are converted to three video fields to make up
a total of five interlaced video frames.
The following diagram demonstrates the process:
Standard 2:3 pulldown is accomplished by representing the first frame of film or
progressive video (frame A) as two fields of video (fields a1 and a2), the second
frame (frame B) as three fields of video (fields b1, b2, and b3), the third frame
(frame C) as two fields (fields c1 and c2), and the fourth frame (frame D) as three
fields (fields d1, d2, and d3). This sequence repeats six times each second.
A B C D
a1 a2 b1 b2 b3 d2 d1 c2 c1 d3
Film frames @ 24 fps or progressive frames @ 23.98 fps
Video fields @ 29.97 fps
Frame A Frame C Frame D Frame B Frame E