How to Work with Layer Masks in Photoshop CS6
Like any other mask in Photoshop CS6, a layer mask is a grayscale image that you can edit to your heart’s content. Layer masks are excellent for blending layers of images together and creating soft transitions between elements.
After you get the concept of layer masks, you’ll never use the eraser tools again. You won’t have to because one of the great things about layer masks is that you can forever edit, or even delete them, with no permanent harm whatsoever to the image.
To create a layer mask, select your desired layer and choose Layer→Layer Mask→Reveal All or Hide All.
Reveal All: Creates a mask filled with white, which shows the layer.
Hide All: Creates a mask filled with black, which hides, or masks, the layer and shows nothing but transparency.
You can also click the Add layer mask icon at the bottom of the Layers panel (which, by default, selects Reveal All). Note that if you already have a layer mask on the layer, this icon will change to Add vector mask. Or you can click the Add a Layer Mask icon in the Properties panel.
You can’t add a layer mask to a Background layer. You must convert the Background layer to a regular layer if you want to use a layer mask on the background of an image.
You can also use an existing selection to create a layer mask. Select your desired layer and make a selection by using one of the selection tools. Choose Layer→Layer Mask→Reveal Selection or Hide Selection. You can also click the Add layer mask button in the Layers panel to create a mask that reveals the selection.
Finally, you can create a mask from the transparent areas of your image. The transparent areas are filled with black on the layer mask.
After you create the layer mask, you can grab the painting tool of your choice and apply your grayscale color.
Add white to the mask to display the image. Add black to hide the image. Add gray to make the layer semitransparent.