Image Mask Parameters

Once you’ve added an image mask to a layer, the following parameters become available in the Image Mask tab of the 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.
  • 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’ve already created.
  • Stencil: When this checkbox is selected, the layer’s geometric transforms are respected by the mask. If you’re creating a mask with transformed Scale, Position, Rotation, or other parameters, select this checkbox to use the modified layer.
  • Stretch: A checkbox that becomes available when Stencil is deselected. Selecting this checkbox stretches the mask to fit the boundaries of the image and centers the mask on the layer’s center point.