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The 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.
7.22.1. Activating the Command
7.22.2. Description of the “Add Layer Mask” Dialog
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Initialize Layer Mask to
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This dialog allows you several choices for the initial contents of
the layer mask:
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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.
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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, leading to
a more transparent layer.
-
Transfer layer's alpha channel
-
This option sets the layer mask as the previous
option, but resets the layer's alpha channel to full
opacity afterwards. 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 visibility of the layer is now
determined by the layer mask alone and not by the
alpha channel. If in doubt, select this option instead
of “Layer's alpha channel”, because it will
leave the appearance unaltered.
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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.
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Channel
-
With this option the layer mask is initialized with a
selection mask you have created before, stored in the
Channel dialog.
-
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.
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