Cinema aspect ratios: flat and scope

A screen has one physical shape, and the two ratios need different shapes. A room built constant height keeps the picture the same height and gets wider for scope — the arrangement most audiences read as "bigger for the big film". A room built constant width keeps the width and loses height for scope, which makes the epic look smaller than the comedy before it.

Either way, the unused part of the screen is where masking comes in: black borders that move to frame the picture so the edges are crisp rather than a grey glow.

The typical failure is a show playlist that plays a scope feature through a flat lens preset, or the reverse — a squashed or cropped picture that nobody in the booth noticed because nobody was in the booth. The fix is procedural: aspect ratio is part of the DCP name, and a playlist check before the first show catches it every time.