This lesson covers, a unique feature known as stack modes in Photoshop. They allow you to combine multiple exposures into a smart object, and then have those images combined mathematically, to possibly display the brightest pixels only, the darkest pixels, average brightness, or other unique results. Those can be useful when stacked on top of the original image in masked, they are especially useful when working with waterfalls. I'll also give you an idea of how I produce the included actions.