Adobe AFTER EFFECTS CS3 PROFESSIONAL User Manual page 535

Posterize Time effect
See also
"Precompose layers" on page 118
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. Once you've applied Time Difference to
locate color differences in footage, use color and levels controls to apply the color corrections.
This effect works with 8-bpc color.
Time Difference effect
Use Time Difference with Particle Playground to shed particles only from moving sections.
Specifies the layer to be compared to the effect layer. The comparison layer's Video switch doesn't need to be
Target
on (unless you select the source layer as the Target).
The relative time in the comparison layer, in seconds, where the layers are compared. If this control is
Time Offset
set to 0.00, the comparison occurs at the current time. To compare the effect layer to a point 3 seconds into the
comparison layer, for example, change the Time Offset value to 3. When you select the underlined offset value, you
can enter the specific frame offset value in the format frames/frame rate. After Effects automatically calculates the
value. For example, enter 3/30 to offset three frames forward in a 30-fps composition. The calculated value is 0.1, or
10% of the total time.
Adjusts the comparison result. This control can be especially helpful in fine-tuning color corrections.
Contrast
Displays the result of the comparison as an absolute value. Any area of the comparison layer
Absolute Difference
that isn't different from the effect layer is represented by black, and any amount of difference is represented as
brighter than black. If this option is unselected, compared areas with no difference are represented as gray.
Specifies how the alpha channel is calculated.
Alpha Channel
•
Uses the effect layer's alpha channel.
Original
•
Uses the target layer's alpha channel.
Target
•
Blends the effect and target layers' alpha channels.
Blend
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