Compatibility of 48 and 24Hz Motion Images: A Problem and a Solution

Shortly after a soundtrack was added to 35mm film in the late 1920s, 24Hz was established as the standard frame rate for sound films. However almost since the ink was dry on that standard, many people on both the technical and creative sides of the industry have lamented that selection as being barely adequate to depict motion properly. As part of their training, cinematographers have to learn how quickly they can move the camera without destroying the illusion of motion¹. Frequently directors have to limit how fast a person or an object moves within a scene for the same reason. It has almost become standard practice for any extremely fast action to be represented in slow motion. For example an explosion will invariably be shown slowed down, likewise a car crash, or even a boxer's punch. This has become part of the standard “cinematic language” such that moviegoers don't question or even notice the practice. But the reason it's done is more rooted in the technology and human psychophysics than the storytelling art – a frame rate of 24Hz isn't really adequate to properly display anything beyond minimal movement. 24Hz is fine for a scene with people simply talking to each other, however almost any kind of “action” scene must either be presented in slow motion, or be carefully staged so the successive movement of objects within the scene from one frame to the next isn't so great that the illusion of motion breaks down.

Published

2008-10

Content type

Original Research

DOI

10.5594/M001050

ISBN

978-1-61482-939-3