Adobe After Effects CS4 - Manual (Page 603)

597 USING AFTER EFFECTS CS4
Effects and animation presets
Last updated 12/21/2009
• Minimum Combines the echoes by taking the minimum pixel values from all of the echoes.
• Screen Emulates combining the echoes by sandwiching them optically. This mode is similar to Add, but it doesn’t
overload as quickly.
• Composite In Back Causes the image from the current time to appear in back, with each echo appearing
successively farther forward in the composite.
• Composite In Front Causes the image from the current time to appear in front, with each echo appearing
successively farther back in the composite.
• Blend Averages the echoes.
More Help topics
“ Precompose layers ” on page 61
Posterize Time effect
The Posterize Time effect locks a layer to a specific frame rate. It’s useful on its own as a special effect, but it also has
more subtle uses. For example, 60-field-per-second video footage can be locked to 24 frames per second (and then field
rendered at 60 fields per second) to give a filmlike look. Also, nested compositions can be locked to a given frame rate.
This effect is sometimes called Strobe in hardware devices.
Animating the value of the Frame Rate slider can give unpredictable results. For this reason, the only interpolation
method allowed for the frame rate is Hold.
This effect works with 8-bpc, 16-bpc, and 32-bpc color.
Posterize Time effect
Note: Another way to accomplish much the same result as applying the Posterize Time effect to a layer is to precompose
the layer, change the frame rate for the precomposition in the Composition Settings dialog box, and set Preserve Frame
Rate When Nested Or In Render Queue for the precomposition on the Advanced tab. This method causes the
precomposition to retain its own frame rate, and not inherit those settings from the containing composition.
More Help topics
“ Precomposing, nesting, and pre-rendering ” on page 60
“ Composition settings ” on page 58
Time Difference effect
The Time Difference effect calculates the color difference between two layers and is a useful aid in color correction;
use it to extract color differences when matching a clean background plate with foreground footage. It’s also good for
creating mattes to be used to apply trails of smoke, fire, or echoing effects. After you apply the Time Difference effect
to locate color differences in footage, you can use Color Correction effects to apply the color corrections.
This effect works with 8-bpc color.