So far we have learned a little bit about layers and how to use them. Today we are going to talk about the most powerful tool in the layers toolkit—the ability to precisely control either by concealing or revealing parts of the layer. Layer masking combined with the selection tools allows the creation of complex composite images. First lets start with little phrase which will be invaluable as you apply these techniques; “White reveals and black conceals”. A layer mask is a grayscale sub-layer which is created when you select the icon at the bottom of the layers palette. These masks go from pure white which shows everything in that layer all the way to pure black, which conceals everything on that layer. The various shades of gray in between will allow some of what is below to come through.
Using the top two layers of the example we have created, we can apply a white layer mask to it. As you can see, it makes no difference at all. However if we click on the layer mask icon, and then select a round brush tool with the color selection set to black, you see what that the layer below shines through. The layer palette looks like this, but is a little difficult to see. By holding down the Alt key while clicking on the layer mask it makes the mast full screen sized. Alt-click the layer mask icon again and it goes back. If you don’t like the results, you can drag the layer mask to the trash can icon at the bottom of the layers palette, just as you can for a layer. It will ask if you want to apply the layer mask before removing, so you want to say “Delete”. You can use other tools as well, such as the gradient tool to gradually transition one image to the other.
So all of these square examples are illustrative, but how do you actually use it? Here is an image of the Rapunzel model from last year’s Photoshop World. I really don’t like the blue background. So I am going to isolate her from it and frame her differently. I create a new layer Ctrl-J and fill it with white Shift-F5. Since the white layer is on top, shetotally disappears, which is not really what we want. To make the next step easier to see, I adjust the transparency of this layer so I can see her coming through—I took it down to about 60%. I then add a layer mask, but I know I want her visible so I invert the mask to make it all black by selecting the layer mask and hitting Ctrl-i. Now the white layer is completely hidden.
I then select a medium sized soft edged brush and check to ensure that the foreground color is white. Start painting around her where you want the white layer to come through as seen here. Finally, bring the layer opacity back up. I found I didn’t like it at full strength so I just took it up to 76%. Could you have just painted on a white layer? Sure, as with almost everything in PS, there are multiple ways to do this, but this gives you a lot more control.