To Separate Video Fields In Imported Footage; To Determine The Original Field Order - Adobe AFTER EFFECTS 7.0 Manual

See also
"To remove 3:2 or 24Pa pulldown from video" on page 102
"To test field-rendering order" on page 597

To separate video fields in imported footage

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 consis-
tently 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 reproduces 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.
When you render a composition containing separated footage, set the Field Rendering option to the same field order
as your video equipment. If you don't field-render the composition, or if you field-render with the incorrect settings,
the final movie may appear too soft, jerky, or distorted.
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. (See "Interpretation methods" on page 73.)
1 Select the footage item in the Project panel.
Choose File > Interpret Footage > Main.
2
Choose an option from the Separate Fields menu.
3
4 Click Preserve Edges (Best Quality Only) to increase image quality in nonmoving areas when the image is
rendered at Best quality. Then click OK.
Note: If the field settings in the Interpret Footage dialog box are correct for the input footage and the field settings in the
Render Settings dialog box are correct for the output device, you can mix footage items of different field orders in a
composition. If either of these settings is incorrect, however, the frames will be in the correct order, but the field order
may be reversed, resulting in jerky, unacceptable images.

To determine the original 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.
Note: Upper-field first corresponds to Even Field First in an ElectricImage file.
Some programs, including After Effects, label the field order when rendering interlaced video files. When you
import a labeled video file, After Effects honors the field order label automatically. You can override the field order
using the interpretation rules file. For more information about field order, see "About field separation and pulldown"
on page 99.
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