Adobe 12040118 - After Effects Standard Tutorial page 479

In both the Persistent and Ephemeral Property Mappers, you can use the alpha channel of a layer map to make more subtle changes to the
value of a particle property. For example, particles over a layer-map pixel in which the alpha channel value is 255 are fully affected, while
lower values affect particles less. Layer-map pixels that are completely transparent have no effect on particle properties.
When you choose any of the following properties, Particle Playground copies the value from the layer map (that is, the layer selected in the
Use Layer as a Map menu) and applies it to the particle.
None Modifies no particle property.
Red, Green, Blue Copy the value of the red, green, or blue channel of a particle within a range of 0.0–1.0.
Kinetic Friction Copies the amount of resisting force against a moving object, typically within a range of 0.0–1.0. Increase this value to slow
down or stop moving particles, as if braking.
Static Friction Copies the amount of inertia that holds a stationary particle in place, typically within a range of 0.0–1.0. At zero, a particle
moves when any other force, such as gravity, is present. If you increase this value, a stationary particle requires more of another force to
start moving.
Angle Copies the direction in which the particle points, in degrees relative to the particle's original angle. The angle is easily observable
when a particle is a text character or a layer without radial symmetry.
Angular Velocity Copies the velocity of particle rotation in degrees per second. This setting determines how fast a particle rotates around its
own axis.
Torque Copies the force of particle rotation. The angular velocity of a particle is increased by a positive torque and is increased more slowly
for particles of greater mass. Brighter pixels affect angular velocity more forcefully; if enough torque is applied against angular velocity, the
particle starts spinning in the opposite direction.
Scale Copies the scale value of a particle along both the x and y axes. Use this control to stretch a particle proportionally. A value of 1.0
scales the particle to its full size; a value of 2.0 scales it 200%, and so on.
X Scale, Y Scale Copy the scale value of a particle along the x or y axis. Use these properties to stretch a particle horizontally or
vertically.
X, Y Copy the position of a particle along the x or y axis in the frame, in pixels. A value of zero specifies a position at the left of the frame
(for X) or at the top of the frame (for Y).
Gradient Velocity Copies the velocity adjustment based on areas of a layer map on both the x and y planes of motion.
X Speed, Y Speed Copy the horizontal speed (x-axis velocity) or vertical speed (y-axis velocity) of a particle in pixels per second.
Gradient Force Copies the force adjustment based on areas of a layer map on both the x and y planes of motion. The pixel brightness
values in the color channel define the resistance to particle force at each pixel, so the color channel acts like a layer map of hills and valleys
that decrease or increase particle force. In the layer map, areas of equal brightness result in no adjustment, similar to flat land. Lower pixel
values represent less resistance to a particle's force, similar to a downhill grade. Higher pixel values represent more resistance to a particle's
force, similar to an uphill grade. For best results, use a soft-edged layer map image.
If you are using a layer map for Gradient Force where flat areas equal no adjustment, and you are using the Min and Max controls (not
the Min or Max operators) to set the range of values for Gradient Force, set them to positive and negative values of the same number (for
example, –30 and +30). This ensures that the middle of the range remains centered at zero.
X Force Copies the coercion along the x axis of motion. Positive values push a particle to the right.
Y Force Copies the coercion along the y axis of motion. Positive values push a particle down.
Opacity Copies the transparency of a particle, where zero is invisible, and 1 is solid. Adjust this value to fade particles in or out.
Mass Copies the particle mass, which interacts with all properties that adjust force, such as Gravity, Static Friction, Kinetic Friction, Torque,
and Angular Velocity. It takes greater force to move particles with a larger mass.
Lifespan Copies the elapsed length of time a particle exists, in seconds. At the end of its lifespan, the particle is removed from the layer.
The default lifespan is effectively immortal.
Character Copies the value that corresponds to an ASCII text character, making it replace the current particle. Applies only if you're using
text characters as particles. You can specify which text characters appear by painting or drawing shades of gray on the layer map that
correspond to the ASCII characters you want. A value of zero produces no character. For US English characters, use values in the range
32–127. The range of possible values can accommodate Japanese characters. For more information about the ASCII character values for a
font you're using, see the documentation for the font, use a utility such as Character Map (Windows), or contact the font manufacturer.
Note: If you simply want to make certain characters spell a message, it's much easier to type the text directly in the Options dialog box.
The Character property is more useful as a secret message effect in which you scramble text characters.
Font Size Copies the point size of characters. Applies only if you're using text characters as particles. Increase this value to make
characters larger.
Time Offset Copies the Time Offset value used by the Layer Map. Applies only if you used the Layer Map control to specify a multiframe
layer (such as a movie) as a particle source.
Scale Speed Copies the scale of a particle. Positive values expand the particle, and negative values shrink the particle. Particles expand or
shrink by a percentage per second.