Ever have a shot where a window is just blasting white? Or maybe the opposite: you can see the view outside a window but the room inside goes pitch dark? Masking is the technique of digitally replacing an area in a shot to correct imbalances in exposure, color, or otherwise. That means we can take two identical shots of an area, one with the interior properly balanced and one with the window properly balanced and digitally merge them together to create an image where both elements are clear and distinguishable.
In these shots, some spectacular views are obstructed by window glare–and we missed sunset. Not a problem.
(Note: In the above “after” shot we also fixed some skewed angles, cloned a burned-out ceiling light, and evened the spread of the recessed lights above the windows.)
Not only is masking incredibly useful in fixing overexposed windows, but it can replace a sky (in case of poor weather or window glare), temper overly bright light fixtures, or insert/remove the image on a television.