Cinema masking

Masking exists because the eye judges black relative to its surroundings. Frame the picture tightly with true black fabric and the image looks deeper and more contrasty than the same image with grey unlit screen around it — no change to the projector at all.

Two conventions exist. Top-and-bottom masking keeps the width constant and moves horizontal borders between flat and scope. Side masking keeps the height constant and moves the sides. Which one a cinema uses is an architectural decision made when the room is built, and it determines which format looks most impressive in that auditorium.

Trailers in flat, feature in scope, masking cue missing from the show playlist. The feature plays letterboxed inside the flat frame with grey bands top and bottom, and it looks wrong for the entire running time.

Audiences do not have the vocabulary for it but they register it immediately, and it is the kind of fault that produces a complaint about the picture being "small" or "dark". It is also entirely preventable: the ratio field in the package name tells you what is coming, and the cue belongs in the playlist before the first performance rather than after the first complaint.