MASKING SEVERAL LAYERS WITH ONE IMAGE

Sometimes you want to mask or crop more than one image with the
same shape. To allow for the most flexibility, use a clipping group
with your layers. In this example we used type as the masking layer
and two different fabric layers. We wanted to leave them on separate
layers to allow for more experimentation.

1. Open or create a file that contains all the layers that you want to mask through a

Common mask. The layer that will mask the others should be the bottom-most layer. In this example we will mask both the lace and the floral layers with the big type layer. Remember to put your mask shape on a transparent background.

Base layer (mask)

The shape that masks all the layers in the clipping group must be on a transparent background or the effect will not work. The masking shape is created by every pixel on the base layer no matter what color it is. The edge of the mask shape is wherever there is a pixel next to a transparent area.

2. Make a clipping group by holding the Option/Alt key and clicking between the layers that will be in the group. Notice how the cursor changes to indicate that you are making a clipping group, and the Layer thumbnail indents.

Group modes

All clipping groups have a base layer. This is the bottom layer in the group, and it defines the shape of the mask through layers in the group are displayed. The base layer defines the mode and transparency of all the layers in its group.

3. Option/Alt clicks between all the layers that will be in the clipping group. Note: You can move layers around within a group, but once you move a layer outside of the group, it will no longer be masked by the base layer.

Clipping groups

As you click the lines between the layers to make a clipping group, they become dotted lines. The base layer is the one with the underlined layer name.

references:

Adobe Seminars: Web Page Design

by Lisa Lopuck and Sheryl Hampton