Photo Tip of the Day: Before and after preview of Photoshop Layers
Preview the before and after effect of your layers in Photoshop with one quick click of the mouse. All you need to do is hold down the Alt. key while clicking on the eyeball to the left of the background layer at the bottom of the adjustment layer stack in the layers window. This really helps you to see where you started to where you have come with your processing so far. See the image below.