Silent film Early
silent films had stated frame rates anywhere from 16 to 24 frames per second (FPS), but since the cameras were hand-cranked, the rate often changed during the scene to fit the mood. Projectionists could also change the frame rate in the theater by adjusting a
rheostat controlling the voltage powering the film-carrying mechanism in the
projector. Film companies often intended for theaters to show their silent films at a higher frame rate than that at which they were filmed. These frame rates were enough for the sense of motion, but it was perceived as jerky motion. To minimize the perceived flicker, projectors employed dual- and triple-blade
shutters, so each frame was displayed two or three times, increasing the flicker rate to 48 or 72 FPS and reducing eye strain.
Thomas Edison said that 46 frames per second was the minimum needed for the eye to perceive motion: "Anything less will strain the eye." In the mid to late 1920s, the frame rate for silent film increased to 20–26 FPS. From 1927 to 1930, as various studios updated equipment, the rate of 24 FPS became standard for 35 mm sound film. Even though the image update rate is low, the fluidity is satisfactory for most subjects. However, when a character is required to perform a quick movement, it is usually necessary to revert to animating
on ones, as
twos are too slow to convey the motion adequately. A blend of the two techniques keeps the eye fooled and controls production cost. Animation for most "
Saturday morning cartoons" firstly introduced in the mid-1960s was produced as cheaply as possible and was most often shot on "threes" or even "fours", i.e. three or four frames per drawing. This translates to only 8 or 6 drawings per second respectively.
Anime is also usually drawn on threes or twos.
Modern video standards Due to the
mains frequency of electric grids, analog television broadcast was developed with frame rates of 50 FPS (most of the world) or 60 FPS (Canada, US, Mexico, Philippines, Japan, South Korea). The frequency of the electricity grid was extremely stable and therefore it was logical to use for synchronization. The introduction of color television technology made it necessary to lower that 60 FPS frequency by 0.1% to avoid "
dot crawl", a display artifact appearing on legacy black-and-white displays, showing up on highly color-saturated surfaces. It was found that by lowering the frame rate by 0.1%, the undesirable effect was minimized. , video transmission standards in North America, Japan, and South Korea are still based on 59.94 images per second. Two sizes of images are typically used: (1080i
interlaced or 1080p
progressive) and (720p). Confusingly,
interlaced formats are customarily stated at half their image rate, , and
double their image height, but these statements are purely custom; in each format, 60 images per second are produced. A resolution of 1080i produces 59.94 or 50 images, each squashed to half-height in the photographic process and stretched back to fill the screen on playback in a television set. The 720p format produces or images, not squeezed, so that no expansion or squeezing of the image is necessary. This confusion was industry-wide in the early days of digital video software, with much software being written incorrectly, the developers believing that only 29.97 images were expected each second. While it was true that each picture element was polled and sent only 29.97 times per second, the pixel location immediately below that one was polled 1/60 of a second later, part of a completely separate image for the next 1/60-second frame. At its native 24 FPS rate, film could not be displayed on 60 FPS video without the necessary
pulldown process, often leading to
judder: to convert 24 frames per second into 60 frames per second, every odd frame is repeated, playing twice, while every even frame is tripled. This creates uneven motion, appearing stroboscopic. Other conversions have similar uneven frame doubling. Newer video standards support 120, 240, or 300 frames per second, so frames can be evenly sampled for standard frame rates such as 24, 48 and 60 FPS film or 25, 30, 50 or 60 FPS video. Of course these higher frame rates may also be displayed at their native rates.
Electronic camera specifications In electronic camera specifications, frame rate refers to the maximum possible rate frames that can be captured (e.g. if the exposure time were set to near-zero), but in practice, other settings (such as exposure time) may reduce the actual frequency to a lower number than the specification frame rate. ==Computer games==