Frame rate
Frame rate (commonly expressed in frames per second or FPS) is typically the frequency (rate) at which consecutive images (frames) are captured or displayed. This definition applies to film and video cameras, computer animation, and motion capture systems. In these contexts, frame rate may be used interchangeably with frame frequency and refresh rate, which are expressed in hertz. Additionally, in the context of computer graphics performance, FPS is the rate at which a system, particularly a GPU, is able to generate frames, and refresh rate is the frequency at which a display shows completed frames.[1] In electronic camera specifications frame rate refers to the maximum possible rate frames could be captured, but in practice, other settings (such as exposure time) may reduce the actual frequency to a lower number than the frame rate.
"Update rate" and "Burst rate" redirect here. For the measurement of computer performance, see Giga-updates per second. For the method of measuring bandwidth based on peak use, see Burstable billing. For the audio sample rate, see Sampling rate.Film and video[edit]
Silent film[edit]
Early silent films had stated frame rates anywhere from 16 to 24 frames per second (fps),[6] 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.[7] Film companies often intended that theaters show their silent films at higher frame rates than they were filmed at.[8] 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 hertz 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."[9][10] In the mid to late 1920s, the frame rate for silent film increased to 20–26 FPS.[9]
Sound film[edit]
When sound film was introduced in 1926, variations in film speed were no longer tolerated, as the human ear is more sensitive than the eye to changes in frequency. Many theaters had shown silent films at 22 to 26 FPS, which is why the industry chose 24 FPS for sound film as a compromise.[11] From 1927 to 1930, as various studios updated equipment, the rate of 24 FPS became standard for 35 mm sound film.[2] At 24 FPS, the film travels through the projector at a rate of 456 millimetres (18.0 in) per second. This allowed simple two-blade shutters to give a projected series of images at 48 per second, satisfying Edison's recommendation. Many modern 35 mm film projectors use three-blade shutters to give 72 images per second—each frame is flashed on screen three times.[9]
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