Have you ever wondered why British television used to look so different from American television? Or why some slow motion looks better (or smoother) than other slow motion? It has largely to do with the frame rate (or frequency) of the moving picture. This is usually measured in frames per second (often stylized FPS) and has historically been a rigidly standardized element of motion picture technology. But new innovations in video have sparked a new era of higher frame rates. (For more on video quality trends, see Twilight of the Pixels – Shifting the Focus to Vector Graphics.)
A Brief History of Frame Rates
The human eye perceives about ten to twelve frames per second as smooth motion. Anything less appears choppy, like a flipbook. The earliest frame rates were variable, as the first motion picture cameras and projectors were hand-crank operated. The projected moving image needed to be cranked at the same pace at which it was filmed, obviously, or the motion would appear too slow or too fast. Filming movement at a high frame rate to be projected at a lower one was referred to as “over-cranking,” which resulted in slow-motion film. Inversely, “under-cranking” during filming resulted in sped-up motion when projected.
Mechanized cranks were developed in the early twentieth century, however frame rates were not widely standardized until the advent of sound accompaniment around the late 1920s. Sound was initially added to motion picture by way of an optical track added to the film strip. Twenty-four frames per second was about the threshold at which quality, decipherable audio could be produced, so this became the standard frame rate in film for years to come (24 FPS is still widely used to this day).
As video and television developed, however, standard frame rates became more diverse in order to accommodate new technology as well as regional standards. The National Television Systems Committee (NTSC) video system became the prevailing video standard for the United States, Canada, much of North/South America and some other parts of the world during the mid-twentieth century, and typically incorporates a frame rate of 30 frames per second. The Phase Alternating Line (PAL) analog video system, in contrast, has been the standard for much of the rest of the world (including the United Kingdom, as well as much of Europe and Asia) and incorporates a frame frequency of 25 frames per second. (To learn more about television in the modern age, see 7 Ways Technology Has Changed Television.)
Why High Frame Rate?
Motion "smoothness" increases along with frame rate, but any significant improvement is difficult, if not impossible, to discern after about 50 frames per second. Above that, it takes some very keen eyesight to decipher any additional smoothness. So why even bother pushing the frame rate beyond 50 frames per second?
As mentioned before, the higher the frame rate of the recording, the smoother the playback will be for slow motion. Video cameras have been capable of capturing 60 frames per second for many years now, mostly for the purpose of slow-motion playback. Sixty FPS video naturally plays back at half speed in a 30-FPS format. Thus, extreme slow motion is one attractive feature of HFR (especially for scientific video). But the major advantage of high frame rate for most practical purposes would probably have to be reduced motion blur.
Depending on which motion picture capture technology is in use (be it video or film) there is a sequence of events that occurs in order to record every frame. If enough motion occurs within the scene being captured during the duration of the capture process (e.g. 1/24 of a second for 24 FPS) then motion blur will likely appear on the resulting frame. So, naturally, the higher the frame rate is, the less vulnerable the image will be to motion blur.
The disadvantages of high frame rate, perhaps obviously, include bulkier files, higher transmission rates, and diversion of resources away from other media parameters (for example, frame size is often compromised to compensate for the increased number of frames). Nevertheless, a number of video cameras, codecs, plugins and display solutions that have adopted the technology are showing some very impressive results.
Consumer digital cameras now have the ability to hit frame rates that are in the thousands, while higher-level professional equipment can apparently go even higher. But higher cost does not necessarily mean higher frame rate. ARRI, for example, currently makes some of the best quality HFR cameras on the market. Currently running at upwards of around $45,000, these professional-level cameras can shoot at about 200 frames per second in full ProRes HD (1080 pixels wide) and about 100 frames per second at 4K resolution.
In contrast, the compact FPS1000 Platinum model can shoot at an amazing 18,500 frames per second in standard definition (640 by 480 pixels) at a fraction of the price of the ARRI. Canon, Red and Sony all carry options on a much broader pricing spectrum, and the list of brands adopting high frame rate is growing.
Although high frame rate may seem excessive, its practical use in variable frame rate video will become apparent, as will the aesthetic advantage of HFR's significant motion blur reduction. While new video technology trends like HFR can take a long while before hitting the mainstream (4K has been trickling down to the consumer for years now) video makers are finding it tremendously useful. In due time, so will the masses.