Opacity mask overview

Learn about opacity masks and how they can create smooth color transitions.

An opacity mask lets you control an object’s transparency using another object, called the masking object. The masking object determines which parts of the masked object are visible, hidden, or partially transparent. You can use any colored object or raster image as the masking object. Adobe Illustrator converts the colors to grayscale to calculate opacity levels—white areas in the masking object reveal the masked object, black areas hide it, and gray areas create varying levels of transparency.

When you create an opacity mask, in the Transparency panel, a thumbnail of the masked object appears on the left, and a thumbnail of the masking object appears on the right. By default, the masked object and the masking object are linked, indicated by a link between the thumbnails in the panel. When you move the masked object, the masking object moves with it. However, the masked object doesn’t move when you move a masking object. To move them independently, you can unlink them in the Transparency panel.

You can move opacity masks between Illustrator and Photoshop. Opacity masks in Illustrator are converted to layer masks in Photoshop and vice versa.