Grayscale Masks

When you create a grayscale mask, you have two options at your disposal: You can either create a mask that hides the layer content (ready for you to reveal underlying content) or one that reveals all (ready for you to hide underlying content). Both have their uses in the scheme of things.

Masks work on the principle that where the mask is black, it hides content directly underneath; where the mask is white, it reveals content directly underneath; where the mask is a shade of black and white, it partially hides the content directly underneath. Put another way: black conceals content, as the night does; white reveals content, as the daylight does; gray partially conceals content, as does a foggy day.

To add a mask to the active layer that does not hide the layer content, choose Layer ^ Layer Mask ^ Reveal All, or click the Add layer mask icon, located at the bottom of the Layers palette (Figure 8-2).

Figure 8-2: Detail from the Layers palette. A—Link layers. B—Add a layer style. C—Add layer mask. D—Create new fill or adjustment layer. E—Create a new group. F—Create a new layer. G—Delete layer.

NOTE You cannot create a mask for a Background layer; you must convert it to a normal layer first by double-clicking it.

When you create a mask, the foreground and background colors change to white and black, respectively. Before you can paint on the mask, you need to switch the colors around by pressing X (white on white doesn't show too well!). Next, select the Brush tool and an appropriate brush tip and then paint on the mask to hide the layer content; paint with white to reveal again (press X to switch colors). "When painting on masks, it helps to turn off the brush dynamics by choosing Clear Brush Controls from the Brushes palette menu, or by checking them off one by one.

NOTE Sometimes, knowing whether you are working on a mask or the layer content can be difficult. You can tell by observing the thumbnails in the Layers palette: The active thumbnail always has a border around it.

To create a mask that hides the layer content initially, choose Layer ^ Layer Mask ^ Hide All, or hold down Alt (Windows), Opt (Mac OS) and then click the Add Layer Mask icon (Figure 8-2), located at the bottom of the Layers palette.

You can also create a Reveal All or Hide All mask based on an active selection. Follow the preceding steps after making sure that a selection is active. Rather than choose Reveal All or Hide All from the Layer Mask submenu, choose Reveal Selection or Hide Selection.

TIP If you would like the mask to have a soft edge, feather the selection. You can do that by choosing Select ^ Feather or pressing Ctrl+Alt+D (Windows), ^+Opt+D (Mac OS) and then entering a value in the Feather Selection dialog box. Alternatively, use the Gaussian Blur filter on the mask after it has been created.

To delete a mask, drag it to the Trash icon in the Layers palette or choose Layer ^ Layer Mask^ Delete. You can also right-click (Windows), Ctrl-click (Mac OS) the mask thumbnail and choose Delete Layer Mask from the contextual menu. You are then asked to apply or delete the mask. If you choose the former, the layer content is changed permanently in line with the mask. If you choose the latter, it is discarded without affecting the layer.

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