Adobe 12040118 - After Effects Standard Tutorial page 480

Min and Max controls for Property Mappers
When the overall range of layer map brightness values is too wide or narrow, use Min and Max to stretch, compress, or shift the range of values
produced by the layer map. The following examples describe when you may want to adjust Min and Max:
You want to set the smallest font size for your text to 10 points and the largest size to 96 points. Set the Min value to 10 and the Max value
to 96.
You set the initial color of a particle and then use a layer map to change particle colors. If you find that the color changes aren't dramatic
enough, you can lower the Min value and raise the Max value to increase the contrast of the color changes.
You set the initial velocity of a particle and then use a layer map to affect the X Speed value. However, you find that the difference between
the fastest and slowest particles is too great. By raising the Min value and lowering the Max value for the layer map channel that is mapped
to the X Speed value, you narrow the resulting range of particle speeds.
You use a layer map to affect the Scale property of particles and find that the smallest particles aren't small enough while the largest
resulting particles are too large. In this case, the entire output range needs to be shifted down; lower both the Min and Max values.
You have a layer map that modifies particles in the opposite direction from the one you want. Swap the Min and Max values, which has the
same result as inverting the layer map.
Note: The alpha channel of the layer map is used as the selection map for the Persistent and Ephemeral Property Mappers.
Operator controls for the Ephemeral Property Mapper
When you use the Ephemeral Property Mapper controls, Particle Playground replaces the value of a particle's property with the value represented
by the layer map pixel at the particle's current location. You can also amplify, attenuate, or limit the resulting values by specifying a mathematical
operator and then using both the value of a particle's property and its corresponding layer map pixel value.
Set Replaces the value of a particle property by the value of the corresponding layer map pixel. For example, to replace the value of a particle
property with the brightness value of the corresponding pixel on the layer map, use Set. This operator is the most predictable and is the default.
Add Uses the sum of the value of a particle property and the value of the corresponding layer map pixel.
Difference Uses the absolute value of the difference of the value of a particle property and the brightness value of the corresponding pixel on the
layer map. Because it takes the absolute value of the difference, the resulting value is always positive. This operator is useful when you want to
limit values to only positive values. If you're trying to model realistic behavior, the Difference operator may not be ideal.
Subtract Starts with the value of a particle property and subtracts the value of the brightness value of the corresponding pixel on the layer map.
Multiply Multiplies the value of a particle property by the brightness value of the corresponding pixel on the layer map and uses the result.
Min Compares the brightness value of the layer map to the value of the particle property and uses the lower value. To limit a particle property so
that it is less than or equal to a value, use the Min operator and set both the Min and Max controls to that value. If you use a white solid as a layer
map, you need only set the Max control to that value.
Max Compares the brightness value of the layer map to the value of the particle property and uses the higher value.
To amplify existing values of properties, try applying the Add operator with positive values or the Multiply operator with values above 1.0. To
attenuate (tone down) property value changes, try applying the Multiply operator using values in the range 0.0–1.0.
Control layers for Particle Playground
Particle Playground can use a control layer to control a particle property, such as opacity. For general information about creating and using control
layers, see Compound effects and control layers.
Regardless of the color depth of the image that you use as a control layer, Particle Playground always uses its red, green, and blue channels as if
each were an 8-bpc grayscale image. If you create a control layer using colors, the Property Mapper property groups in Particle Playground can
extract the brightness values from each RGB color channel separately.
The alpha channel in a control layer modifies the color values in the control layer before Particle Playground uses the control layer's pixel values.
Areas where the alpha channel value is 0 (transparent areas of a control layer) don't affect particle values. Areas where the alpha channel has a
value greater than 0 (semitransparent and opaque areas of a control layer) affect the particle value to a degree proportional to the value of the
alpha channel. When you use the Persistent and Ephemeral Property Mapper property groups, the range set for the Min and Max controls also
affects the value applied to a particle.
Particle Playground can extract brightness values separately from the red, green, and blue channels in an image. If you want to create different
layer maps for each channel, use a program that can edit individual color channels, such as Adobe Photoshop, and then paint or paste each layer
map into its own channel. Save the control layer as an RGB image in a format After Effects can import. The image may look unusual when viewed
in RGB mode, because it's intended to be used as a single hidden layer containing three different layer maps, not as a visible image layer.
If you already have three separate images, you can combine them into a single RGB file by using the Set Channels effect. Set Channels can
load each image into its own channel in a combined file, making it suitable for use as an RGB layer map.
Improving performance with Particle Playground
Keep in mind the following when working with the Particle Playground effect:
When you're generating a Particle Playground effect, keep an eye on the Info panel to see how many particles are being produced. If an