What Is a Mask in Photoshop?

The term “mask” isn’t immediately understandable to someone outside the realm of graphic design. At its simplest definition a mask is a way to apply something to a very specific portion of an image.There is two primary types of masks: clipping masks and layer masks. These two tools are closely related in concept, but very different in application.

Layer Masks: A layer mask is something that you apply to a given layer to control the transparency of that layer. Where layer opacity controls the transparency of the entire layer at once, a mask gives you more precise controls over very specific areas. If you want the entire layer to be at 30%, you would lower the opacity, if you want just the left side of a layer to be at 30%, you would use a mask. On this invisible canvas, you can paint white, black or any level of gray in-between. The color that you paint tells Photoshop how opaque to make the pixels at that point. White means 100% opacity and black means 0% opacity. There are ways to see it that we’ll check out later but just know that as a general rule, applying a mask to a layer won’t cause any immediate visual differences unless you have an active selection at the time.

Clipping Masks: Clipping masks are very similar to layer masks only they use one layer to determine the transparency of another. In this scenario, you stack two layers on top of each other with the bottom being the determining factor of the transparency of the top. Instead of using black and white values though, clipping masks simply borrow transparency from the layers used to make them, namely the bottom layer. If the bottom layer has some areas that are opaque and some areas that are transparent, a clipping mask will apply these values to the top layer.