ADOBE AFTER EFFECTS 7.0
User Guide
597
Note:
Do not use stretching to change the vertical dimensions of a movie with field rendering. Stretching vertically mixes
the field order, which distorts any motion. Use either cropping or composition nesting if you need to vertically resize a
field-rendered movie.
Crop the composition
To enlarge a movie by a few pixels, increase the size using negative values for the Crop options
in the Output Module Settings dialog box. For example, to increase the size of a movie by 2 pixels, type
–2
in the
Cropping section of the Output Module Settings dialog box. Remember that negative cropping adds to one side of a
movie, so objects originally centered in the composition may not appear centered when the movie is cropped.
Note:
Adding an odd number of pixels to the top of a field-rendered movie reverses the field order. For example, if you
add one row of pixels to the top of a movie with Upper Field First field rendering, the field-rendering order then becomes
Lower Field First. Remember that if you add pixels to the top of the movie, you need to crop from the bottom row of the
movie to maintain the original size. (See “About field separation and pulldown” on page 99.)
Creating low-resolution movies for testing motion
You can test the motion of a high-quality composition by quickly creating a low-resolution, or thumbnail, movie. Do
this by making a movie at a resolution less than full (using the Resolution pop-up menu in the Render Settings dialog
box). After Effects creates a movie with dimensions proportional to the resolution.
For example, if your composition is 640 x 480 pixels and you make a movie at quarter resolution, the resulting movie
will be 160 x 120 pixels (one-sixteenth the size of the composition). This thumbnail renders almost 15 times faster
than at full resolution. You can then play the thumbnail on your system to get a good idea of what motion will be like
in your final, full-sized movie. You can also enlarge the thumbnail in a movie-playing application to see playback at
full size. In addition, you can use RAM preview for testing purposes.
To test field-rendering order
When you render a composition containing separated footage, set the Field Rendering option to the same field order
as your video equipment. If you field-render with the incorrect settings, the final movie may appear too soft, jerky,
or distorted. A simple test can determine the order in which your video equipment requires fields.
Note:
The field order might get altered if you change the hardware or software of your production setup. For example,
changing your device control software or VCR after setting the field order can reverse your fields. Therefore, any time
you make a change to your setup, test the field-rendering order.
The test takes about 15 to 20 minutes and involves creating two movie versions of the same composition (one
rendered with Upper Field First and one with Lower Field First), and then playing the movies to see which choice
looks right.
1
Create a simple composition with the correct frame size and frame rate. Choose an NTSC or PAL preset in the
Composition Settings dialog box, and make the composition at least 3 seconds long.
2
Within the composition, make a layer that is a small rectangular solid. The layer can be any color as long as it
contrasts sharply with the composition background. You may wish to add a title, such as “Upper Field First,” to the
solid to make identification of the movie easier.
3
Apply some fast movement to the solid using keyframes in its Position property. Set keyframes from the upper left
of the Composition panel to the lower right for 1 second.
4
Save the project, and then drag the composition to the Render Queue panel.
5
Click the underlined Render Settings name, and then choose Upper Field First from the Field Render menu.
6
Click OK, and then click Render to make the movie.
