Introduction to Layer Masks

Step 1 First of all you should know what a mask is. A mask is just what it sounds like; it defines what parts of the layer can be seen. Just like if you were to put on a real mask, like a ski mask, the mask would cover most of your face, but leave your eyes and mouth exposed. If we put a mask on a layer, we get to decide which parts of the layer are seen, and which parts allow the layers below to be exposed. Let's do a quick example to help you get the concept. Let's say that you had an image open in Photoshop with the two layers below.

Step 2 The boxes are the same size, so the only part of the image you would see is the green box. Let's say you wanted some of the red box to show through, this can be accomplished with a layer mask. I can add a layer mask to the green layer and draw a big X. This would tell Photoshop that wherever I draw, let the layer(s) below show through.

Step 3 Let's look at how to accomplish this exactly. Create a new image, and make two layers. I am using the two layers shown below, but you can use anything you want. Right now, all you will see is the top layer, but we will add a mask so that some of the bottom layer shows through. Click on the top layer and go to Layer>Add Layer Mask>Reveal All.

Step 4 You will notice that once you select Reveal All, your layers palette changes.

Step 5 This is the layer mask itself. Notice that it is all white at the moment, and your image did not appear to change. Layer masks only consist of 2 colors, white and black. White means that you should see the layer, and black means that you should see the layers below. To illustrate, I will draw a big, black X with the paintbrush on the layer mask.

Step 6 As you can see, the place where I drew the black X lets the layer below show through. You can use any tool on the layer mask, but you can only use the colors white and black. If you ever want to edit the mask itself, you have to click directly on the mask, not just anywhere on the layer.

Step 7 I'm going to edit the layer mask. I will fill in the black X with all white so that the entire layer is showing again. This time, I am going to trace around the guy with black so that the background shows through. I had to use a smaller brush for some of the details. This process is very forgiving, meaning that if you make a mistake you can always switch from black to white and erase part of it and vice-versa.

Step 8 In the above image we used Reveal All to start with. Now we'll look at an example where you'd want to use Hide All. Let's say you wanted make the image grayscale, but you wanted certain parts to still be in the original color. You would duplicate the layer and convert the bottom layer to grayscale. Then click on the top layer and go to Layer>Add Layer Mask>Hide All.

Step 9 Now you can edit the layer mask and color in white with the paintbrush on the parts of the layer that you want to be visible.

Step 10 In this case I will color on the layer mask with white over the end of the gun and the guy's face shield.

Step 11 Now we'll do one more example, but this time we will use the gradient tool instead of the paintbrush. This is where the real power of layer masks comes in. In this example I will use the original guy in the top layer, and the same image in the bottom layer. However on the bottom layer I will do a radial blur.

Step 12 I went to Layer>Add Layer Mask>Reveal All on the top layer. Now, Instead of simply painting with the paintbrush, I took the gradient tool and used a white to black gradient with Radial selected. I started on the guy's head and dragged the gradient out into the image about halfway. You can see how the circle fades from white to black on the layer mask itself where I drew the gradient. This allows the layer below to fade in, in the radial shape that the gradient made instead of being strictly defined with the paintbrush. This is one of the most powerful uses of layer masks, the ability to fade two layers together any way you want.

Step 13 The best way to figure it out from here is to get some images and play around with it. Once you understand the concept, it won't take long for you to see where a layer mask could be beneficial somewhere in almost every project.