Apple Motion 3 - Manual (Page 1095)

Chapter 12 Using Shapes and Masks 1095
 Intersect: Masks that are set to intersect do not replace an object’s original alpha
channel. Instead, they mask out all regions of the object that do not overlap the
mask itself. This includes other masks applied to the same object that appear nested
underneath the intersecting mask in the Layers tab. In the following example, only
the overlapping areas of the rectangle and circle masks are opaque. Everything else
is transparent.
Invert Mask: When this checkbox is selected, the mask is inverted—its solid and
transparent areas are swapped. This is useful if you need to switch the solid and
transparent areas of a mask you have already created.
Tip: You can apply different filters and effects to the foreground and background of an
image by first masking the foreground subject, duplicating the layer and its mask, then
inverting the duplicate layer’s mask. Effects that are applied to the background can
then be completely isolated from the foreground, or vice versa.
Note: You can adjust the opacity of a mask in the Properties tab of the Inspector.
Feather: A slider that feathers (softens) the edges of a mask. Positive feathering values
soften the edge of the mask from its edge outward. Negative feathering values soften
the edge of a mask inward from the edge. Feathering the edge of a mask can soften a
harsh rotoscoping job, making the masked object blend more easily with the
background.
Control Points: Click the disclosure triangle to display the Position parameters for the
mask control points. Use the value sliders to adjust the position of a control point. The
left value slider represents X and the right value slider represents Y.