Adobe After Effects CS3 - Manual (Page 509)

AFTER EFFECTS CS3
User Guide
504
3 Choose a property for each of the Map Red To, Map Green To, and Map Blue To controls. You don’t have to map
properties to all of the color channels. For example, if you want to change scale over an image map, you can map the
color red to scale without setting other properties.
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 a layer map’s alpha channel 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 trans-
parent 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 particle’s red, green, or blue channel 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 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 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 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.