Adobe AFTER EFFECTS 5.5 Help Manual page 43

Adobe After Effects Help
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Using interlaced video in After Effects
If you want to use interlaced or field-rendered footage (such as from NTSC video) in an
After Effects project, you will get the best results if you separate the video fields when you
import the footage. After Effects separates video fields by creating a full frame from each
field, preserving all of the image data from the original footage.
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. See
"Removing 3:2 pulldown from video transferred from film" on page 45.
Separating fields
Separating fields is critical if you plan to make significant changes to the footage. When
you scale, rotate, or apply effects to interlaced video, unwanted artifacts, such as crossed
fields, are often introduced. By separating fields, After Effects accurately converts the two
interlaced frames in the video to noninterlaced frames, while preserving the maximum
amount of image quality. Using noninterlaced frames allows After Effects to apply edits
and effects consistently and at the highest quality.
After Effects creates field-separated footage from a single formerly interlaced field by
splitting fields into two independent frames. Each new frame has only half the information
of the original frame, so some frames may appear to have a lower resolution than others
when viewed at Draft quality. When you render the final composition, After Effects repro-
duces high-quality interlaced frames for videotape. When you render a movie at Best
quality, After Effects interpolates between the scan lines of a field to produce maximum
image quality.
Note: After Effects automatically separates fields for D1 and DV video footage files. You
can manually separate fields for all other types of video footage in the Interpret Footage
dialog box. For more information, see "Specifying interpretation rules" on page 27.
To separate video fields in imported footage:
1 Select the footage item in the Project window.
2 Choose File > Interpret Footage > Main.
3 Select an option from the Separate Fields pop-up menu.
4 Click Motion Detect to increase image quality in nonmoving areas when the image is
rendered at Best quality. Then click OK.
Interpreting field order
Interlaced video has a field order defining the order in which the two video fields (upper
and lower) are displayed. A system that draws the upper lines before the lower lines is
called upper-field first; one that draws the lower lines before the upper lines is called lower-
field first. The order in which the fields are displayed is important, especially when the
fields contain motion. If you separate video fields using the wrong field order, motion will
not appear smooth.
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