Adobe Illustrator CS3 - Manual (Page 184)

ILLUSTRATOR CS3
User Guide
178
2 Select either of the following options in the Transparency panel:
Clip Gives the mask a black background which crops the masked artwork to the boundaries of the masking object.
Deselect the Clip option to turn off the clipping behavior. To select clipping for new opacity masks by default, select
New Opacity Masks Are Clipping from the Transparency panel menu.
Invert Mask Reverses the luminosity values of the masking object, which reverses the opacity of the masked artwork.
For example, areas that are 90% transparent become 10% transparent after the mask is inverted. Deselect the Invert
Mask option to return the mask to the original state. To invert all masks by default, select New Opacity Masks Are
Inverted from the Transparency panel menu.
If these options aren’t visible, select Show Options from the panel menu.
Use transparency to shape a knockout
You can use the Opacity & Mask Define Knockout Shape option to make a knockout effect proportional to the
object’s opacity. In areas of the mask that are close to 100% opacity, the knockout effect will be strong; in areas with
less opacity, the knockout effect will be weaker. For example, if you
use a gradient-masked object as a knockout,
the underlying object will be knocked out progressively, as if it were being shaded by a gradient. You can create
knockout shapes with both vector and raster objects. This technique is most useful for objects that use a blending
mode other than Normal.
1 Do one of the following:
• To use an opacity mask to shape the knockout, select the masked artwork, and then group it with the objects you
want to knock out.
• To use the alpha channel of a bitmap object to shape the knockout, select a bitmap object that contains trans-
parency, and then group it with the objects you want to knock out.
2 Select the group.
3 In the Transparency panel, select Knockout Group until the option displays a checkmark.
4 Among the grouped objects, target the masking objects or transparent image in the Layers panel.
5 In the Transparency panel, select Opacity & Mask Define Knockout Shape.