Adobe AFTER EFFECTS CS3 PROFESSIONAL User Manual page 354

Expression Controls effects
Expression Controls effects do not modify existing layer properties; rather, these effects add layer properties that
expressions can refer to. (See "Using Expression Controls effects" on page 551.)
Preventing edge clipping with the Grow Bounds effect
Because an effect is applied to a layer, the results of some effects are constrained to the layer's bounds, which can
make the effect appear to end abruptly. You can apply the Grow Bounds effect to a layer to temporarily extend the
layer for the purpose of calculating the results of other effects. This process is not necessary for newer effects, which
tend to be 32-bpc effects.
See also
"About plug-ins" on page 40
"Layer switches and columns in the Timeline panel" on page 151
About compound effects and control layers
Several effects rely on a control layer as input. These compound effects use the pixel values of the control layer to
determine how to affect the pixels of the layer that the effect is applied to. For example, the Displacement Map effect
uses the color values of a control layer to determine how far to shift pixels of the underlying layer, and in which
direction. The compound effect ignores effects, masks, and transformations of a control layer, unless the layer has
been precomposed. It is common to use a control layer that is not itself visible—that is, its Video switch
Most compound effects include a Stretch Map To Fit option (or a similarly named option), which temporarily
stretches or shrinks a control layer to the effect layer's dimensions. This provides a pixel in the control layer corre-
sponding to each pixel in the effect layer. If you deselect this option, the compound effect's calculations are
performed as if the control layer is centered on the effect layer at its original size.
For many compound effects, neutral gray pixels in the control layer correspond to null operations. This makes a
neutral gray solid layer a good starting point for creating a control layer. Apply the Fractal Noise effect to a layer and
precompose it to create a good control layer for turbulent or atmospheric results.
Effects with a Comp Camera attribute
Some effects can use a composition's camera and lights. These effects include Card Dance, Card Wipe, and Shatter.
Some of these effects always use the composition camera, whereas others include light and camera options in the
Effect Controls panel.
When you apply an effect with a Comp Camera attribute to a 2D layer, the effect can track the composition's camera
and light positions and render a 3D image on the 2D layer that it is applied to. The effect's results appear 3D; however,
the layer with the Comp Camera attribute applied remains a 2D layer and consequently has the following character-
istics:
• 3D layers above and below it in the Timeline panel cannot intersect with each other or cast shadows on each other.
• It cannot intersect with 3D layers or cast or accept shadows.
Note: The image is rendered on the layer, not the composition, so make sure that you apply these effects to layers that
are the same size as the composition and are exactly centered in the composition.
AFTER EFFECTS CS3 348
User Guide
is off.