Adobe AFTER EFFECTS 5.5 Help Manual page 373

Adobe After Effects Help
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Selection Map Choose a layer map that influences which particles are affected by the
current option (see "About layer maps (PB only)" on page 374). Selection is based on the
brightness, or luminance, of each pixel in the layer, so a particle is affected more or less as
it passes over layer map pixels of different brightness. By default, a property affects a
particle 100% where the brightness value of a corresponding layer map pixel is 255
(white), and has no effect where the brightness value of a corresponding layer map pixel is
0 (black).
Note: The simulation space is not bounded by the dimensions of the layer to which
Particle Playground is applied. You may need to use a selection map that is larger than the
Playground layer so that dots that are not visible are still affected by Selection Map
options.
Characters Choose a text field containing the characters you want to be affected by the
current option. This option applies only if you are using text characters as the particle type.
For example, if you're setting up the Gravity property and you define a text field
containing the characters A, E, I, O, and U, the current option affects those characters only.
(The Characters option is case-sensitive.) To define the text fields, click Options at the top
of the Particle Playground effect controls section, type text in Selection Text 1, Selection
Text 2, and Selection Text 3 as necessary, and click OK. (The characters you type here are
also case-sensitive.) Once you've created selection text, choose the selection from the
Characters menu under Affects. For more information, see "Replacing default particles
with text (PB only)" on page 361.
Older/Younger Than Specify the age threshold, in seconds, above or below which you
want a particle to be affected by the current option. Specify positive values to affect older
particles, or negative values to specify younger particles. For example, if you set this
option to 10, all particles older than 10 seconds use the new value. As soon as a particle
reaches 10 seconds, it changes to the new value.
Age Feather Specify the age range in seconds within which the Older/Younger Than
value is feathered, or softened. Feathering creates a gradual, rather than abrupt, change.
For example, if you set Older/Younger Than to 10 and Age Feather to 4, about 20% of
particles will start changing when they're 8 seconds old, 50% will change when they're 10
seconds old (the Older/Younger Than value), and the remainder will change by the time
they're 12 seconds old.
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