A hand-cranked history
Frame rate refers to the number of images displayed by a projector within one second. In the early days of cinema, silent movies were shot by hand-cranked cameras at frame rates of anywhere from 14 to 24 frames per second (FPS), and played back at roughly the same rate. When “The Talkies” were born, effectively ending the silent movie era, a steady playback speed was needed to keep the audio in these new sound movies synchronized with the visuals. Using more frames meant more costs for film and processing, and studio bosses found 24 frames per second was the cheapest, minimally acceptable frame rate they could use for showing these new “talking” movies with relatively smooth motion.
That 24 FPS standard is still around today, almost a century later. Since the late 1920s, projectors have been using shutter systems that show the same frame two or three times to boost the overall frame rate. That reduces much of the flicker audiences would otherwise see, but it’s still not enough to keep up with the fast motion of action movies and sweeping, panning shots.
The jerkiness that’s just become a part of conventional filmmaking is visually accentuated in 3D, because watching eyes are working particularly hard to focus on moving objects.
How frame rates work in 3D digital cinema
For single projector systems, alternating images are shown to the left and right eyes of people in the audience, who are wearing some type of 3D eyewear – either polarized, shuttered or spectral division glasses.
For the 3D movies that have already been running in theaters, the current generation of DLP® Cinema™ projectors are showing the movies at 24 FPS, but actually flashing each frame image three times. Called triple-flashing, it means viewers are actually seeing 144 frames per second. The flashing is done to eliminate any perception (and therefore the distraction) of the sequential progression of frames.
While it’s still too soon to know if multiple image flashing will be as important with HFR content, the technology to accomplish this will be included in every HFR-capable Christie projector. Shot at high frame rates, new 3D movies would be double-flashed by projectors to remove any hint of flickering. Fans watching a film produced at 48 FPS would see the same frame flashed twice per second, resulting in 96 FPS seen by each eye and 192 FPS overall.
Films produced at 60 FPS, and then double-flashed, would result in movie-goers seeing a 3D film at an ultra-smooth 240 FPS. The television industry is already using much higher frame rates of between 50 and 60 frames per second, with some of those standards dating back to the 1940s. Consumers with HD services and HDTVs are now accustomed to watching content that delivers extremely smooth motion and crisp, vivid detail. Sports and live events are now routinely captured and broadcast in high frame rate HD, elevating consumer assumptions on how things should look. [more…]