Apple Motion 4 - Manual (Page 320)

Blend Modes
While the Opacity parameter simply defines a uniform level of transparency for an object,
the blend modes allow you many more creative options to control how the overlapping
images interact, based on the colors in each object. By default, each object’s blend mode
is set to Normal, so that changes to an object’s opacity uniformly affect every part of the
image equally.
Blend modes can create transparency in an object regardless of the setting of its Opacity
parameter. This is because the pixels of an image with a selected blend mode are
combined with the pixels of any objects lying immediately below in the Canvas. For
example, if you overlap two objects, then set the blend mode of the top one to Screen,
the darker areas of the screened image become transparent, while the lighter areas remain
more solid, resulting in the following image:
Important: The transparency created by most of the available blend modes only affects
how an object combines with overlapping objects underneath. These blend modes do
nothing to affect an object’s alpha channel. For information about blend modes that do
affect an object’s alpha channel, see
Blend Modes That Manipulate Alpha Channels .
Each blend mode combines objects in different ways. For example, setting the top object’s
blend mode to Multiply yields a result opposite to that of the Screen blend mode, as the
darker areas of the image remain solid, and the lighter areas become transparent.
320 Chapter 7 Basic Compositing