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DigitalVideoAndHDTVAlgorithmsAndInterfaces.pdf

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Figure 36.1 “2-3 pulldown”<br />

refers to transfer of film at about<br />

24 frames per second to video at<br />

about 60 fields per second. The<br />

first film frame is transferred to<br />

two video fields; the second<br />

frame is transferred to three. The<br />

2-3 cycle repeats. SMPTE<br />

RP 197 denotes film frames as<br />

A, B, C, and D. The A-frame is<br />

unique in being associated with<br />

exactly two fields, first then<br />

second, of a single video frame.<br />

(“A-frame” denotes both a film<br />

frame and a video frame.)<br />

According to SMPTE RP 201,<br />

this video frame should have<br />

timecode ending in 0 or 5. The<br />

midframe (M-frame) is the video<br />

frame which comprises one field<br />

from each of two film frames.<br />

2-3 pulldown 36<br />

Motion picture film originates at 24 frames per second.<br />

Many television programs, including the majority of<br />

prime-time programs, originate on film at this rate. This<br />

chapter discusses the conversion of film to video at<br />

frame rates different from the native 24 Hz of film.<br />

Film has historically been transferred to 480i29.97<br />

video using a technique called 2-3 pulldown, whereby<br />

successive film frames are scanned first twice then three<br />

times to produce five video fields. The process is then<br />

repeated, reversing the roles of the first and second<br />

fields. The scheme is sketched in Figure 36.1:<br />

A<br />

B<br />

C<br />

D<br />

Video fields Timecode<br />

1 :x0, :x5<br />

2<br />

1<br />

2<br />

1<br />

2<br />

1<br />

2<br />

1<br />

2<br />

A-frame<br />

Midframe<br />

(M-frame)<br />

:x1, :x6<br />

:x2, :x7<br />

:x3, :x8<br />

:x4, :x9<br />

429

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