Layer Masks
Photopedia
14 July 2008 11:11
Layer Masks are used to hide or reveal parts of the layers below. Parts of one layer can be hidden while others are revealed to create a new combined image. They're non-destructive so you can edit them infinately without any risk of damage to your shot. Masking allows you to create seamless blends between layers. It's an advanced Photoshop tool that can be as simple or as complicated as you make it. Beginners with an understanding of layers will have no problem moving onto a basic application of layer masks.
To create a Layer Mask you will need to be working on the layer that you would like to add a mask to. You can then either click the add Layer Mask button at the botom of the layer palette (see accompanying image), or go to Layer > Layer Mask > Reveal All or Hide All. Reveal all will give you a white mask and hide all will give you a black mask. The default setting when adding a mask via the layer palette is Reveal All. The reason for this is that with masking, black hides parts of the image while white will allow them to show through (remember that your layer stack will also affect what is visible).
The mask is visible on the layer in the form of a thumbnail next to the layer thumbnail. When you want to work on the mask, you must ensure you've clicked the mask thumbnail so that it's highlighted. If you simply click the layer, this is what you'll be working on, not the Mask.
To apply the mask you will now have to paint in it with black to hide the layer it's attached to, and white to do the opposite, it really is that simple. To have more control over your painting you can soften or harden your brush, change the brush opacity and use shades of grey alongside black and white.
Note: To create a layer mask on the Background layer you must convert it to a normal layer (Layer > New > Layer from Background) the default setting will rename it Layer 0.