Adjustment layers wouldn’t be so wonderful if they always affected the entire image. To get adjustment layers to strut their stuff, combine them with layer masks, which allow you to limit which areas of the image will be affected by each adjustment layer. Let’s look at all the ways in which we can work with layer masks and adjustment layers.
By default, each adjustment layer comes equipped with a layer mask. This mask appears to the right of the Adjustment icon. If no selection is present when the adjustment layer was created, the layer mask will be entirely white. In a layer mask, all white causes the adjustment to affect the entire image. Black, on the other hand, prevents the adjustment from affecting areas. ...