Apple Motion 5.1.1 - Manual (Page 905)

Chapter 20 Shapes, masks, and paint strokes 905
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Blue: Uses the blue channel as a grayscale mask.
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Alpha: Uses the alpha channel from the mask layer.
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Luminance: Uses the aggregate luminance from the red, green, and blue channels as a
grayscale mask.
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Mask Blend Mode: A pop-up menu that determines how an image mask interacts with the
alpha channel of the layer to which it is applied. When a layer has multiple image masks,
each mask can have a different Mask Blend mode. When this happens, each mask adds to,
or subtracts from, the layer’s alpha channel according to the selected mode. The final alpha
channel is the combined result of all image masks applied. These modes are identical to the
Mask Blend Mode options available for shape masks. The four options are:
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Add: Adds the mask to the alpha channel (the default setting). This is useful for adding back
regions of an image that other masks are cutting out.
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Subtract: Subtracts a mask from the alpha channel. This is useful for creating holes in the
middle of layers, or for masking out additional regions of an image that are untouched by
other masks.
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Replace: Replaces the layer’s original alpha channel, as well as any other masks applied to the
same layer that appear underneath the current mask in the Layers list, with the current mask.
You can add masks above, set to whatever blending mode you like.
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Intersect: Masks out all regions of the layer that do not overlap the mask itself (but does not
replace a layer’s original alpha channel). This includes other masks applied to the same layer
that appear nested underneath the intersecting mask in the Layers list.
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Invert Mask: A checkbox that reverses the mask—its solid and transparent areas are swapped.
This is useful if you need to switch the solid and transparent areas of an existing mask.
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Stencil: A checkbox that preserves the layer’s geometric transforms. If you’re creating a mask
with transformed Scale, Position, Rotation, or other parameters, select this checkbox to use the
modified layer.
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Stretch: A checkbox, available when Stencil is deselected, that stretches the mask to fit the
boundaries of the image and centers the mask on the layer’s center point.
Convert between shapes and masks
Because masks and shapes are created in similar ways but perform different tasks, there are
occasions where you may create a shape and later want to convert it into a mask, or vice versa.
Changing shapes to masks and masks to shapes is done by changing the object’s position in the
Layers list or by using the Object menu.
Note: Masks are not applicable to 3D paint strokes, 3D particle systems or replicators, 3D text
objects or unflattened 3D groups. To convert a shape to a mask on such an object, the item must
be flattened.
Different options are available when converting shapes to masks, depending on the type of
object being masked. When you need to convert a shape to a mask, consider the following:
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When a shape is converted to a mask and applied to a scaled object, the resulting mask is
scaled as well. This may lead to unexpected results. To prevent surprises, set the object to 100%
scale or place the object in a new group and apply the mask to the group.
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Converting a shape that has been manipulated in 3D into a mask may produce unexpected
results. For more information on applying masks to 3D objects, see
Mask objects in a 3D
project on page 891.
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