5

Applying Behaviors to Image Masks
You can also apply behaviors to image masks to create animated transparency effects.
For more information, see Applying Behaviors to Masks.
Image Mask Parameters
After you add an image mask to a layer, the following parameters become available in
the Image Mask Inspector.
Image Mask Parameters in the Inspector
The Image Mask HUD contains the Mask Source, Source Channel, Mask Blend Mode, Invert
Mask, Stencil, and Stretch parameters. These controls, and the additional parameters in
the Inspector, are described below.
Mask Source: An image well that assigns a layer (a shape, text, an image, a movie, particle
emitter, numbered image sequence, and so on) to use to mask a layer.
Frame: When you use a movie or image sequence as the assigned image, this slider
allows you to select the start frame for playback.
Hold Frame: When you use a movie or an image sequence as the assigned image,
selecting this checkbox freezes the frame specified in the Frame parameter. That frame
is then used as the mask for the masked layer’s total duration.
Offset: Offsets the X and Y values of the mask’s position, relative to the layer it is masking.
This allows you to change which part of the layer is masked.
Wrap Mode: If an image mask is smaller than the layer it is assigned to, you can increase
the area it affects by selecting a wrap mode from this pop-up menu. There are three
options:
• None: The object is used as is.
• Repeat: The object is duplicated and tiled to fill up the full width and height of the
image.
• Mirror: The layer is duplicated, tiled, and reversed to fill up the full width and height
of the image. This may create a more seamless repetition for some images.
Source Channel: A pop-up menu that lets you choose which channel of the assigned
image is used to create the mask. There are five choices:
• Red: Uses the red channel as a grayscale mask.
• Green: Uses the green channel as a grayscale mask.
• Blue: Uses the blue channel as a grayscale mask.
• Alpha: Uses the alpha channel from the mask layer.
• Luminance: Uses the aggregate luminance from the red, green, and blue channels as
a grayscale mask.
1219Chapter 20 Using Shapes, Masks, and Paint Strokes