Traditionally a ruby lith, a transparent deep red material, was used as a mask. The mask covered and protected parts of an image. The masks were cut with an X-acto™ knife and the process was tedious, taxing, and tiresome.

With Photoshop this process has been simplified. Make a single or multiple Selections. Shifted Selection allows for adding to Selections. The resulting area outside the selection automatically becomes a mask.

Sometimes this outside/inside thing can get confusing. No problem, it is easy to reverse a mask. Inverse the selection (Shift+Ctrl+I).

Use the resulting mask, modify it, or even save it for later use. Eliminate any masks or Selections with Ctrl+D.

This is a much easier and faster process than making a new mask in the traditional X-acto™ method.

Save masks to the alpha channel. The Select > Save Select... opens the Save Selection dialog box.

Click OK and accept the default settings.

Click on the Channels tab to see the result. The new channel is inactive (no eye icon).

Notice that the Display box is missing the eye icon.

The mask shape is shown as a b/w mini icon with a #4 label. The mini mask icon shows the exact silhouette in black and white.

Activate the mask by clicking in the empty Display box. The eye icon appears and the red mask becomes visible over Stevie (see sample below).

The active mask color resembles the traditional ruby lith. Everything under the mask is protected.

All changes to the image will occur in the non-masked area, the wall behind Stevie. Multiple masks can be used and masks can also be affected by any of the modifiers which interact with the Selections tool. In this example, the wall is also masked but the mask has been modified by Feather (Selections > Feather... value 3).

Notice that the Channels Palette now shows two mask channels and the new mask icon even reflects the feathering.

The next topic is Layers.