Apple Shake 4 - Manual (Page 116)

116 Chapter 3 Adding Media, Retiming, and Remastering
Pulldown and Pullup
3:2 Pulldown is a technique to temporally convert the framerate of noninterlaced film
footage to that of video, and back again. The pulldown parameter in the Timing tab of
SFileIn allows you to manage your pulldown/pullup of a sequence. There are two
options:
30 to 24
This option removes pulldown from a media file that has been telecined to 30 fps. Use
this setting to return it to 24 fps for compositing in Shake.
24 to 30
This option converts 24 fps film footage to 30 fps—adding 3:2 pulldown.
dominance
When you select either option, an additional dominance parameter appears which lets
you select the field dominance of the output.
More About 3:2 Pulldown
Film uses frames, running at 24 frames per second (fps). Video uses interlaced fields,
with the frame rate of NTSC video running at 29.97 fps, and the frame rate of PAL video
running at 25 fps. To convert a film sequence into a video sequence, you need to split
the film frames into fields, and double up two out of every five frames in order to make
24 film frames fill the space of 30 video frames per second. To use the classic graph:
The third and fourth frames have fields that blend to stretch time. It’s called 3:2
because you have three solid frames and two mixed frames.
To fully reconstruct the original four film frames (in time, not resolution—the original
resolution is already lost), you must extract the field data from the five video frames.
But there is usually a complication—when you receive your footage, it has probably
already been edited. As a result, there is no guarantee that frames 3 and 4 are the
mixed frames because all of the clips have been shifted in the edit. As a result, you
need to determine what the first frame is.
To determine the first frame of an image sequence with 3:2 pulldown:
1 Double-click the FileIn node to load its image in the Viewer and its parameters into the
Parameters1 tab.
2 In the Time Bar, move the playhead to the first frame in the sequence, and scrub
through the first five frames while looking at the Viewer to determine the first frame
that shows two fields from different frames that are blended together.
1/6 of a Second Equals
4 Film Frames A B C D
5 Video Frames AA BB BC CD DD