Adobe 12040118 - After Effects Standard, Руководство

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video overview of fields and interlacing on the Lynda.com website
Remove 3:2 or 24Pa pulldown from video
When you transfer 24-fps film to 29.97-fps video, you use a process called 3:2 pulldown, in which the film frames are distributed across video
fields in a repeating 3:2 pattern. The first frame of film is copied to fields 1 and 2 of the first frame of video, and also to field 1 of the second video
frame. The second frame of film is then spread across the next two fields of video—field 2 of the second video frame and field 1 of the third frame
of video. This 3:2 pattern is repeated until four frames of film are spread over five frames of video, and then the pattern is repeated.
The 3:2 pulldown process results in whole frames (represented by a W) and split-field frames (represented by an S). The three whole video frames
contain two fields from the same film frame. The remaining two split-field frames contain a video frame from two different film frames. The two split-
field frames are always adjacent to each other. The phase of 3:2 pulldown refers to the point at which the two split-field frames fall within the first
five frames of the footage.
Phase occurs as a result of two conversions that happen during 3:2 pulldown: 24-fps film is redistributed through 30-fps video, so each of four
frames of 24-fps film is spread out over five frames of 30(29.97)-fps video. First, the film is slowed down 0.1% to match the speed difference
between 29.97 fps and 30 fps. Next, each film frame is repeated in a special pattern and mated to fields of video.
When you apply 3:2 pulldown to footage, one frame of the film (A) is separated into two or three interlaced video fields (B) which are grouped into
video frames containing two fields each.
When importing interlaced video that was originally transferred from film, you can remove the 3:2 pulldown that was applied during the transfer
from film to video as you separate fields so that effects you apply in After Effects don’t appear distorted.
It’s important to remove 3:2 pulldown from video footage that was originally film so that effects you add in After Effects synchronize perfectly with
the original frame rate of film. Removing 3:2 pulldown reduces the frame rate by 1/5—from 30 to 24 fps or from 29.97 to 23.976 fps, which also
reduces the number of frames you have to change. To remove 3:2 pulldown, you must also indicate the phase of the 3:2 pulldown.
After Effects also supports Panasonic DVX100 24p DV camera pulldown, called 24P Advance (24Pa). Some cameras use this format to capture
23.976 progressive-scan imagery using standard DV tapes.
Before you remove 3:2 pulldown, separate the fields as either upper-field first or lower-field first. Once the fields are separated, After Effects can
analyze the footage and determine the correct 3:2 pulldown phase and field order. If you already know the phase and field order, choose them
from the Separate Fields and the Remove menus in the Interpret Footage dialog box.
1. In the Project panel, select the footage item from which to remove 3:2 pulldown.
2. Choose File > Interpret Footage > Main.
3. In the Fields and Pulldown section, select Upper Field First or Lower Field First from the Separate Fields menu.
4. Do one of the following and click OK:
If you know the phase of the 3:2 or 24Pa pulldown, choose it from the Remove menu.
To have After Effects determine the correct settings, click Guess 3:2 Pulldown or Guess 24Pa Pulldown.
Note: If your footage file contains frames from different sources, the phase may not be consistent. If the phase is inconsistent, import
the footage multiple times, once for each phase, and interpret each footage item with a different setting. Then, add each footage item to
your composition and trim each layer to use only the appropriate frames. In other words, if you have an asset that has multiple pulldown
phases, then you need to cut that asset into pieces and remove pulldown separately for each of the pieces. This can come up if the
asset is a movie that has been edited together from several sources in an NLE.
Online resources about pulldown
Chris Meyer provides a video tutorial on identifying pulldown on the Lynda.com website .
Chris and Trish Meyer provides an overview of 3:2 pulldown in an article on the Artbeats website .
Chris Meyer provides links to resources about pulldown on the ProVideo Coalition website .