.To show or hide the underlying layers completely with the new mask, choose from the Show All or Hide All Layer menu commands.
Other ways to create a new mask layer: On the Layer palette, right-click the layer to which you want to add a mask and choose New Mask Layer > Show All to show all underlying pixels or Hide All to hide all underlying pixels. (Or, click the Show All button on the Layer palette.)
To create a new mask layer:
On the Layer palette, click the layer you want to mask.
Choose Layers > New Mask Layer and then choose the type of mask:
Show All Shows all underlying pixels. All pixels of the mask are white. Paint the mask with greys or black to hide portions of the underlying layers.
Hide All Hides all underlying pixels. All pixels of the mask are black. Paint the mask with white or greys to show portions of underlying layers.
The mask layer and the selected layer are added to a new layer group. The mask layer applies to the selected layer only. To apply it to all underlying layers, drag it from the layer group to the main level.
To view the mask on the image, on the Layer palette click the Mask Overlay toggle .
If you chose a show mask layer, the underlying layer appears unchanged; paint on the image to hide portions of the underlying layers. If you chose a hide mask layer, the mask completely hides the underlying layer; paint on the image to show portions of the underlying layer. For more information on editing the mask, see Editing Masks.
Creating Masks from Selections