How to Mask & replace skies with Photoshop

Learn how to combine images with a mask in Adobe Photoshop by opening the same raw file twice and applying separate exposures. This technique is used to perhaps mask out the sky or the windows. Using the negative exposure making the initially over exposed sky black and the dark parts white which is what the mask feature operates on. Then the designer selects cuts out the sky in the mask layer and makes it invisible so that the second layer or underlying picture shows through.