Adobe After Effects CS4 - Manual (Page 671)

665 USING AFTER EFFECTS CS4
Expressions
Last updated 12/21/2009
Argument type: valOrArray is a Number or an Array [2 or 3].
Returns a number in the range from -1 to 1. The noise is not actually random; it is based on Perlin noise, which means
that the return values for two input values that are near one another will also tend to be near one another. This type of
noise is useful when you want a sequence of seemingly random numbers that don’t vary wildly from one to the other—
as is usually the case when animating any apparently random natural motion. Example:
rotation +
360*noise(time)
Interpolation methods (expression reference)
For all of the Interpolation methods, the argument t is often time or value , though it can have other values, instead.
If t is time , the interpolation between values happens over a duration. If t is value , then the expression maps one
range of values to a new range of values.
For additional explanations and examples of the Interpolation methods, see JJ Gifford’s website .
Ian Haigh provides a script on After Effects Scripts website that you can use to easily apply advanced interpolation
method expressions—such as bounces—to properties.
linear(t, tMin, tMax, value1, value2) Return type: Number or Array.
Argument type: t, tMin, and tMax are Numbers, and value1 and value2 are Numbers or Arrays.
Returns value1 when t <= tMin. Returns value2 when t >= tMax. Returns a linear interpolation between value1 and
value2 when tMin < t < tMax.
For example, this expression on the Opacity property causes Opacity values to ramp linearly from 20% to 80% over
the time from 0 seconds to 6 seconds:
linear(time, 0, 6, 20, 80)
This method—like all of the Interpolation methods—can also be used to convert from one range of values to another.
For example, this expression on the Opacity property converts the Opacity values from the range 0%-100% to the range
20%-80%:
linear(value, 0, 100, 20, 80)
linear(t, value1, value2) Return type: Number or Array.
Argument type: t is a Number, and value1 and value2 are Numbers or Arrays.
Returns a value that linearly interpolates from value1 to value2 as t ranges from 0 to 1. Returns value1 when t <= 0.
Returns value2 when t >= 1.
ease(t, value1, value2) Return type: Number or Array.
Argument type: t is a Number, and value1 and value2 are Numbers or Arrays.
Similar to linear with the same arguments, except that the interpolation eases in and out so that the velocity is 0 at
the start and end points. This method results in a very smooth animation.
ease(t, tMin, tMax, value1, value2) Return type: Number or Array.
Argument type: t, tMin, and tMax are Numbers, and value1 and value2 are Numbers or Arrays.
Similar to linear with the same arguments, except that the interpolation eases in and out so that the velocity is 0 at
the start and end points. This method results in a very smooth animation.
easeIn(t, value1, value2) Return type: Number or Array.
Argument type: t is a Number, and value1 and value2 are Numbers or Arrays.