Adobe AFTER EFFECTS 5.5 Help Manual page 369

Adobe After Effects Help
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You have a layer map that modifies particles in the opposite direction from the one you
•
want. Swap the Min and Max values, which will have the same effect as inverting the
layer map.
Note: The alpha channel of the layer map is used as the selection map for the Persistent
and Ephemeral Property Mappers. See "Using Affects options to specify particles (PB only)"
on page 372.
Using Ephemeral Property Mapper operators to adjust values (PB
only)
By default, Particle Playground replaces the value of a particle's property with the value
represented by the layer map pixel at the particle's current location. You can also amplify,
attenuate, or limit the resulting values by specifying a mathematical operator in the
Ephemeral Property Mapper, and then using both the value of a particle's property and its
corresponding layer map pixel value. Operators are available only in the Ephemeral
Property Mapper. The following operators are available:
Set Replaces the value of a particle property by the value of the corresponding layer map
pixel. This is the default operator.
Add Uses the sum of the value of a particle property and the value of the corresponding
layer map pixel.
Difference Uses the absolute value of the difference of the value of a particle property
and the brightness value of the corresponding pixel on the layer map. Because it takes the
absolute value of the difference, the resulting value is always positive. This operator is
useful when you want to limit values to only positive values. If you're trying to model
realistic behavior, the difference operator may not be ideal.
Subtract Starts with the value of a particle property and subtracts the value of the
brightness value of the corresponding pixel on the layer map.
Multiply Multiplies the value of a particle property by the value of the brightness value of
the corresponding pixel on the layer map and uses the result.
Min Compares the brightness value of the layer map to the value of the particle property
and uses the lower value.
Max Compares the brightness value of the layer map to the value of the particle property
and uses the higher value.
If you are not familiar with mathematical operators, the following guidelines can help you
decide whether you should use an operator:
The most predictable operator to use is Set, which is the default, because it simply
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replaces the value of a particle property with the value of the brightness value of the
corresponding pixel on the layer map.
To amplify existing values of properties, try applying the Add operator with positive
•
values or the Multiply operator with values above 1.0.
To attenuate (tone down) property value changes, try applying the Multiply operator
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using values between 0 and 1.0.
To limit a particle property so it is less than or equal to a value, use the Min operator and
•
set both the Min and Max properties to that value. If you use a white solid as a layer
map, you need only set the Max property to that value.
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