Adobe After Effects CS4 - Manual (Page 604)

598 USING AFTER EFFECTS CS4
Effects and animation presets
Last updated 12/21/2009
Time Difference effect
Use Time Difference with Particle Playground to shed particles only from moving sections.
Target Specifies the layer to be compared to the effect layer. The Video switch for the comparison layer doesn’t need
to be on (unless you select the source layer as the Target).
Time Offset The relative time in the comparison layer, in seconds, where the layers are compared. If this control is 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.
Contrast Adjusts the comparison result. This control can be especially helpful in fine-tuning color corrections.
Absolute Difference Displays the result of the comparison as an absolute value. Any area of the comparison layer 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.
Alpha Channel Specifies how the alpha channel is calculated.
• Original Uses the alpha channel of the effect layer.
• Target Uses the alpha channel of the target layer.
• Blend Blends the alpha channels of the target layer and the effect layer.
• Max Uses the more opaque of the alpha channels.
• Full On Sets the alpha channel to completely opaque.
• Lightness Of Result Uses the lightness of the RGB difference as alpha.
• Max Of Result Uses the highest values of the RGB difference as alpha.
• Alpha Difference Calculates differences in the alpha channels of the effect layer and target layer in the same way in
which RGB difference is calculated.
• Alpha Difference Only Calculates only the differences in the alpha channels. RGB is set to white.
Time Displacement effect
The Time Displacement effect distorts the image by shifting pixels across time, producing a wide variety of effects. For
example, the traditional slit-scan technique, which captures different stages of a moving image across time, can be
simulated using the Time Displacement effect.
This effect works with 8-bpc and 16-bpc color.