Movie theaters have to work harder and harder to entice viewers away from their big-screen TVs and same-day streaming options. The most important difference has to be in the quality of the viewing experience, and Screen Crush reports that they are increasingly failing at the most basic requirement — getting the screen proportions right. In saving money via automation, they lose the ability to make sure that each individual film is shown the way it was intended to be shown.

Screen masking involves expanding or shrinking the borders of a theater screen so that a film fills its dimensions exactly. Most mainstream movies are released in one of two aspect ratios: 1.85:1, also known as “flat” and the taller of the two, and 2.35:1, known as “scope” and the wider of the two. Masking ensures that both aspect ratios are displayed on the same screen with none of the image being lost, and none of the unused areas of the screen left visible.

Because movies come in both sizes, and because theaters often show multiple movies at the same time, screens must be built to accommodate both aspect ratios and then masked, either on the sides or on the top and bottom, with black curtains. If you’ve ever arrived early at the theater and noticed motorized curtains retract between the multiplex’s pre-show (which is typically flat) and the feature presentation (which in this case would be scope), you’ve seen screen masking in action.

If you see a film that looks distorted or otherwise not optimally displayed, speak to a manager.