The Add Layer Mask command adds a layer mask
to the active layer. It displays a dialog in which you can set the
initial properties of the mask. If the layer already has a layer mask,
or if it cannot have one because it does not have an alpha channel, the
menu entry is insensitive and grayed out.
A layer mask lets you define which parts of the layer are opaque,
semi-transparent or transparent.
See the Layer Mask
section for more information.
10.29.1.
Activating the Command
You can access this command from the image menubar through
Layer->Mask->Add Layer Mask
or from the pop-up menu you get by right-clicking on the active
layer in the Layers Dialog.
10.29.2.
Description of the “Add Layer Mask” Dialog
Figure 10.105.
The “Add Layer Mask” dialog
Initialize Layer Mask to
This dialog allows you six choices for the initial contents
of the layer mask:
White (full opacity)
With this option, the layer mask will make all of the
layer fully opaque. That means that you will not
notice any difference in the appearance of the layer
until you paint on the layer mask.
Black (full transparency)
With this option, the layer mask will make all of the
layer fully transparent. This is represented in the image
by a checkered pattern on which you will need to paint
to make any part of the layer visible.
Layer's alpha channel
With this option, the contents of the alpha channel are
used to fill the layer mask. The alpha channel itself is
not altered, so the transparency of partially visible
areas is increased.
Transfer layer's alpha channel
This option does the same thing as the previous option,
except that it also resets the layer's alpha channel to full
opacity. The effect is to transfer the transparency
information from the alpha channel to the layer mask,
leaving the layer with the same appearance as before.
The only difference is that the visibility of the layer
is now determined by the layer mask and not by the alpha
channel.
Selection
This option converts the current selection into a layer
mask, so that selected areas are opaque, and unselected
areas are transparent. If any areas are partially
selected, you can click on the
QuickMask
button to help you predict what the effects will be.
Grayscale copy of layer
This option converts the layer itself into a layer mask.
It is particularly useful when you plan to add new
contents to the layer afterwards.
Invert Mask
If you check the Invert Mask box at the
bottom of the dialog, the resulting mask is inverted, so that
transparent areas become opaque and vice versa.
When you click on the OK button, a thumbnail
of the layer mask appears to the right of the thumbnail of the layer
in the Layers Dialog.
Published under the terms of the GNU General Public License
