Adobe After Effects CS4 - Manual (Page 577)

571 USING AFTER EFFECTS CS4
Effects and animation presets
Last updated 12/21/2009
4 Specify the minimum and maximum values you want the layer map to produce for each Map To group. Min is the
value to which a black pixel is mapped, and Max is the value to which a white pixel is mapped. The complete tonal
distribution between Min and Max is then scaled proportionally.
5 If using the Ephemeral Property Mapper, you can apply an operator to the value of a particle property and the value
of the corresponding layer map pixel.
Note: Because particle properties use many kinds of units, such as pixels, degrees, and seconds, you may want to compress
or expand the range of values from the layer map so that all the resulting values are usable in the measurement system of
a specific particle property. First, use the Min and Max controls, which define the range of values to use from the layer
map. If further adjustment is necessary and you’re using the Ephemeral Property Mapper, use the Operator control and
choose a mathematical operator to amplify, attenuate, or limit the effect of a layer map.
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