Masks and transparency overview
Masks are a special type of shape used to create regions of transparency in layers. When you create a mask to define transparency in a layer, you’re drawing a shape to use as that layer’s alpha channel. (For more information about drawing shapes and masks, see Draw simple masks and Draw complex shapes and masks.) Because a layer’s alpha channel is a grayscale channel, masks are grayscale objects, where white defines solid areas, progressively darker levels of gray define decreasingly opaque areas, and black defines areas of complete transparency.
You can apply masks to layers that already have an alpha channel, to add to, subtract from, intersect, or replace the layer’s original alpha channel. You can also use another layer as an image mask to mask a layer. For more information, see Image masks overview.
This section describes how to:
Mask a layer, then adjust the mask
Combine multiple masks to isolate complex contours
Make advanced adjustments to masks in the Mask Inspector
Important: When a mask is applied to a 2D group or a flattened 3D group, the group is rasterized. For more information, see Shapes and rasterization.