Technical data

70 Using Layers and Masks
2 Editing on the Mask
In Edit Mask mode, you can use the full range of painting tools,
selection options, and effects to alter the mask’s grayscale values.
These manipulations cause corresponding changes in opacity, which in
turn changes the appearance of the pixels on the layer itself.
Remember, as long as you are editing the mask, you’re only seeing a
preview of changes on the layer. No permanent changes will be applied
until you actually merge the mask with the layer. You can switch out of
Edit Mask mode at any time to work directly on the layer (or any other
part of the image), then switch back to resume work on the mask.
To edit the active layer’s mask, check Edit Mask on the Layers menu.
(Uncheck to discontinue editing the mask.)
The image window’s titlebar shows “[MASK],”
indicating that a mask is currently being edited.
The Color tab switches to Grayscale mode when
you’re editing a mask, and reverts to the previous
setting when you exit Edit Mask mode. This
means anything you paste from the Clipboard
onto the mask will automatically be converted to
grayscale.
In Edit Mask mode, you’re normally viewing not the mask, but rather
the effects of changes “as if” you were making them on the layer below.
Adding a Reveal All mask can be a bit confusing, because there’s
initially no evidence the mask is there at all (i.e. the layer appears
exactly the same as it did before you added the mask)! It’s sometimes
helpful to switch on the View Mask setting (on the Layers menu),
which hides the layer and lets you see only the mask, in all its black,
white, or grayscale glory. For example, a Reveal All mask appears pure
white in View Mask mode (as at right).
This represents a clear mask with no
effect on the underlying pixels’ opacity.
View Mask can also be useful in the
latter stages of working on a mask, to
locate any small regions that may have
escaped your attention.
You can disable the mask (check Disable Mask on the Layers menu)
to see how the layer looks without the mask’s effects. Note that
disabling the mask is not the same as cancelling Edit Mask mode—it
only affects your view of the layer, not which plane (i.e. mask or layer)
you’re working on.