Adobe AFTER EFFECTS CS3 PROFESSIONAL User Manual page 536

• Uses the most opaque of the original source and Target layers' alpha channels.
Max
• Sets the alpha channel to completely opaque.
Full On
• Uses the lightness of the RGB difference as alpha.
Lightness Of Result
•
Uses the highest values of the RGB difference as alpha.
Max Of Result
•
Calculates differences in the effect and target layers' alpha channels the same way RGB
Alpha Difference
difference is calculated.
•
Calculates only the differences in the alpha channels. RGB is set to white.
Alpha Difference Only
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.
Time Displacement effect
Like the Displacement Map effect, the Time Displacement effect uses a displacement map, but it bases the movement
of pixels in the layer on luminance values in the map. Pixels in the layer that correspond to bright areas in the
displacement map are replaced by pixels in the same position but at a specified number of seconds forward in time.
Likewise, pixels in the layer that correspond to dark areas in the displacement map are replaced by pixels at a
specified number of seconds backward in time. You can use any layer as a displacement map, though using a
grayscale image lets you more easily see brightness levels and predict how pixels will be displaced.
The Time Displacement effect automatically replaces pixels across time without keyframes or expressions. However,
you can animate other properties to vary the effect over time.
To better understand how pixels are displaced in time, think of the displacement occurring in steps, as follows:
After Effects overlays the displacement map layer on top of the effect layer (the layer you're distorting). If the
1
dimensions of the displacement map are different from those of the effect layer, you can specify whether the map is
centered or stretched to fit.
2 You specify a maximum displacement amount, in seconds.
After Effect uses the luminance value of each pixel in the displacement map to calculate the displacement of the
3
corresponding pixel in the effect layer, based on the maximum displacement amount.
In grayscale images, the luminance value range extends from 0 to 255, and it's converted to a scale ranging from -1
to 1. A luminance value of 0 produces maximum backward displacement, meaning that pixels at the current time are
replaced by pixels from a previous time. A luminance value of 255 produces maximum positive displacement,
meaning that pixels at the current time are replaced by those at a future time. A luminance value of 128 produces no
displacement. For other values in grayscale displacement maps, you can calculate the displacement amount, in
seconds, using the following equation:
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