High Frame Rate Video Playback

By RED Digital Cinema

The advent of digital cinematography has opened up new creative possibilities for how motion is captured. This article explores the influence of high frame rate (HFR) video playback, along with the associated motivations and controversy, with an eye for what this might hold for the future of cinema.

Background

Although modern cinema uses a 24 fps time base, early film was projected with a wide variety of speeds. Prior to the 1930’s, many silent films used just 15-20 fps, since this is when the illusion of continuous imagery begins. Then, with the advent of audio, frame rates were increased to the now-standard 24 fps, primarily because this was the minimum rate that would still produce acceptable audio when read from a 35 mm film reel.

In any case, the overall strategy was to use as little film as possible. None of the motivations were to maximize the viewer’s sense of realism — footage was just deemed “good enough” without being prohibitively expensive. However, with digital capture, we’re no longer bound by the same rules. Recent and upcoming productions are beginning to explore high frame rate (HFR) playback. HFR is already being used for sports and other HDTV broadcasts, and in cinema, Avatar 2 and The Hobbit are known productions targeting HFR release.

Motivations

Even though about 15 fps is needed to initiate the illusion of continuous motion, the effect by no means stops there. Visual studies have shown that even if one cannot distinguish discrete images, a frame rate all the way up to 60-80 fps makes footage appear more lifelike by enhancing clarity and smoothness.

HFR also minimizes the appearance of motion artifacts — especially when viewed in a theater. Moving objects may strobe or have a “picket fence” appearance as they traverse a large screen. At 24 fps, a 50 foot screen shows an object as jumping in 2 foot increments if that object takes one second to traverse the screen. This can appear as “judder” with fast panning and other types of camera movements.

Everything else being equal, one can also extract sharper and more precisely positioned stills with HFR. This is particularly helpful when a fashion video will also be used as a stills photo shoot, or when movie frames need to be pulled for print advertising. If HFR output isn’t needed, at 48 fps one can always use frame skipping for backward compatibility with 24 fps.

HFR can also make the viewing experience more enjoyable by reducing eye-strain and fatigue. Since our visual system is designed to process continuous imagery, discrete footage can sometimes be tiring during extended viewing — just as with flickering from CRT monitors or fluorescent lights. With 3D in particular, viewing fatigue is often cited as one of the biggest impediments to more widespread adoption.

Projectors also have the potential to brighten with HFR. With 24 fps, movie projectors typically show each frame 2-3 times for an overall refresh rate of 48-72 Hz. However, if those flashes are too bright, each frame will appear to flicker. With HFR, a frame is flashed fewer times — permitting brighter projection without the associated flickering. [more...]

Source: RED Digital Cinema

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