Apple Motion 4 - Manual (Page 324)

The effect that each blend mode has on overlapping objects depends on the range of
color values within each object. The red, green, and blue channels within each overlapping
pixel are mathematically combined to yield the final image.
These value ranges can be described as blacks, midrange values, or whites. These regions
are loosely illustrated by the chart below.
Blacks Whites Midrange color values
For example, the Multiply blend mode renders color values that fall into the white areas
of an image transparent, while the black areas of the image are left alone. All midrange
color values become translucent, with colors falling into the lighter end of the scale
becoming more transparent than the colors that fall into the darker end of the scale.
Group Blend Modes
Blend modes work differently depending on whether they’re used with groups or layers.
In particular, the Pass Through blend mode is available only for groups.
Pass Through
When a group is set to Pass Through, each object is individually blended with all objects
and groups that appear underneath it in the Layers tab. In this example, the Swirls object
is set to Stencil Luma, and the Fishes object is set to Add.
324 Chapter 7 Basic Compositing