A frame line is the unused space that separates two adjacent images, or film frames , on the release print of a motion picture . They can vary in width; A 35 mm film with a 1.85: 1 hard mattehas a frame line of approximately 8 millimeters (0.3 inches) high, having both a full frame negative and the anamorphic format having very narrow frame lines, with the frames very close together. When a film is properly projected, the frame should not be visible to the audience and is typically cropped out of projection with an aperture mask.