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Frame rate

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(Redirected fromFramerate)
"Update rate" and "Burst rate" redirect here. For the measurement of computer performance, seeGiga-updates per second.For the method of measuring bandwidth based on peak use, seeBurstable billing.For the audio sample rate, seeSampling rate.

Frame rate,most commonly expressed inframes per secondorFPS,is typically thefrequency(rate) at which consecutiveimages(frames) are captured or displayed. This definition applies tofilmandvideo cameras,computer animation,andmotion capturesystems. In these contexts, frame rate may be used interchangeably withframe frequencyandrefresh rate,which are expressed inhertz.Additionally, in the context of computer graphics performance, FPS is the rate at which a system, particularly aGPU,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.

Human vision

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Further information:Motion perception

The temporal sensitivity and resolution ofhuman visionvaries depending on the type and characteristics of visual stimulus, and it differs between individuals. The humanvisual systemcan process 10 to 12 images per second and perceive them individually, while higher rates are perceived as motion.[2]Modulated light (such as acomputer display) is perceived as stable by the majority of participants in studies when the rate is higher than 50 Hz. This perception of modulated light as steady is known as theflicker fusion threshold.However, when the modulated light is non-uniform and contains an image, the flicker fusion threshold can be much higher, in the hundreds of hertz.[3]With regard toimage recognition,people have been found to recognize a specific image in an unbroken series of different images, each of which lasts as little as 13 milliseconds.[4]Persistence of visionsometimes accounts for very short single-millisecond visual stimulus having a perceived duration of between 100 ms and 400 ms. Multiple stimuli that are very short are sometimes perceived as a single stimulus, such as a 10 ms green flash of light immediately followed by a 10 ms red flash of light perceived as a single yellow flash of light.[5]

Film and video

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Silent film

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Earlysilent filmshad 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 arheostatcontrolling the voltage powering the film-carrying mechanism in theprojector.[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-bladeshutters,so each frame was displayed two or three times, increasing the flicker rate to 48 or 72 hertz and reducing eye strain.Thomas Edisonsaid 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

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Whensound filmwas 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-bladeshuttersto 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]

Animation

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Thisanimated cartoonof agalloping horseis displayed at 12 drawings per second, and the fast motion is on the edge of being objectionably jerky.

In drawnanimation,moving characters are often shot "on twos", that is to say, one drawing is shown for every two frames of film (which usually runs at 24 frame per second), meaning there are only 12 drawings per second.[12]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 without unnecessary production cost.[13]

Animation for most "Saturday morning cartoons"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.Animeis also usually drawn on threes or twos.[14][15]

Modern video standards

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See also:List of broadcast video formats

Due to themains frequencyof electric grids, analog television broadcast was developed with frame rates of 50 Hz (most of the world) or 60 Hz (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.

As of 2021,video transmission standards in North America, Japan, and South Korea are still based on 60/1.001 ≈ 59.94 images per second. Two sizes of images are typically used: 1920×1080 ( "1080i/p" ) and 1280×720 ( "720p" ). Confusingly,interlacedformats are customarily stated at 1/2 their image rate, 29.97/25 FPS, anddoubletheir 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 1920×540 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 59.94/50 or 29.97/25 1280×720p 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, which was incorrect. 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 Hz video without the necessarypulldownprocess, 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.[16][17]

Electronic camera specifications

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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 frame rate.[18]

Computer games

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Incomputer video games,frame rate plays an important part in the experience as, unlike film, games are rendered inreal-time.60 frames per second has for a long time been considered the "optimal" frame rate for smoothly animated game play.[19]Video games designed forPALmarkets, before thesixth generation of video game consoles,had lower frame rates by design due to the 50 Hz output. This noticably made fast-paced games, such as racing or fighting games, run slower.[20]

Frame rate up-conversion

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Frame rate up-conversion (FRC) is the process of increasing thetemporal resolutionof a video sequence by synthesizing one or more intermediate frames between two consecutive frames. A low frame rate causesaliasing,yields abrupt motion artifacts, and degrades the video quality. Consequently, the temporal resolution is an important factor affecting video quality. Algorithms for FRC are widely used in applications, including visual quality enhancement, video compression and slow-motion video generation.

Low frame rate video
Video with 4 times increased frame rate

Methods

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Most FRC methods can be categorized intooptical flowor kernel-based[21][22]and pixel hallucination-based methods.[23][24]

Flow-based FRC

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Flow-based methods linearly combine predicted optical flows between two input frames to approximate flows from the target intermediate frame to the input frames. They also propose flow reversal (projection) for more accurateimage warping.Moreover, there are algorithms that give different weights of overlapped flow vectors depending on theobject depthof the scene via a flow projection layer.

Pixel hallucination-based FRC

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Pixel hallucination-based methods use deformableconvolutionto the center frame generator by replacing optical flows with offset vectors. There are algorithms that also interpolate middle frames with the help of deformable convolution in the feature domain. However, since these methods directly hallucinate pixels unlike the flow-based FRC methods, the predicted frames tend to beblurrywhen fast-moving objects are present.

See also

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References

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  1. ^Tamasi, Tony (3 December 2019)."What is Frame Rate and Why is it Important to PC Gaming?".Retrieved12 February2023.
  2. ^abRead, Paul; Meyer, Mark-Paul; Gamma Group (2000).Restoration of motion picture film.Conservation and Museology. Butterworth-Heinemann. pp. 24–26.ISBN978-0-7506-2793-1.
  3. ^James Davis (1986), "Humans perceive flicker artefacts at 500 Hz",Sci. Rep.,5:7861,doi:10.1038/srep07861,PMC4314649,PMID25644611
  4. ^Potter, Mary C. (December 28, 2013)."Detecting meaning in RSVP at 13 ms per picture"(PDF).Attention, Perception, & Psychophysics.76(2): 270–279.doi:10.3758/s13414-013-0605-z.hdl:1721.1/107157.PMID24374558.S2CID180862.Archived(PDF)from the original on 2022-10-09.
  5. ^Robert Efron (1973)."Conservation of temporal information by perceptual systems".Perception & Psychophysics.14(3): 518–530.doi:10.3758/bf03211193.
  6. ^Brown, Julie (2014)."Audio-visual Palimpsests: Resynchronizing Silent Films with 'Special' Music".In David Neumeyer (ed.).The Oxford Handbook of Film Music Studies.Oxford University Press. p. 588.ISBN978-0195328493.
  7. ^Kerr, Walter (1975).Silent Clowns.Knopf. p.36.ISBN978-0394469072.
  8. ^Card, James (1994).Seductive cinema: the art of silent film.Knopf. p.53.ISBN978-0394572185.
  9. ^abcBrownlow, Kevin (Summer 1980)."Silent Films: What Was the Right Speed?".Sight & Sound.49(3): 164–167. Archived fromthe originalon 8 July 2011.Retrieved2 May2012.
  10. ^Elsaesser, Thomas; Barker, Adam (1990).Early cinema: space, frame, narrative.BFI Publishing. p. 284.ISBN978-0-85170-244-5.
  11. ^TWiT Netcast Network (2017-03-30),How 24 FPS Became Standard,archivedfrom the original on 2021-11-04,retrieved2017-03-31
  12. ^Chew, Johnny."What Are Ones, Twos, and Threes in Animation?".Lifewire.RetrievedAugust 8,2018.
  13. ^Whitaker, Harold; Sito, John Halas; updated by Tim (2009).Timing for animation(2nd ed.). Amsterdam: Elsevier/Focal Press. p. 52.ISBN978-0240521602.RetrievedAugust 8,2018.{{cite book}}:CS1 maint: multiple names: authors list (link)
  14. ^"Shot on threes (ones, twos, etc.)".Anime News Network.
  15. ^CLIP STUDIO (12 February 2016)."CLIP STUDIO PAINT アニメーション cơ năng の sử い phương".Archivedfrom the original on 2021-11-04 – via YouTube.
  16. ^High Frame-Rate Television,BBC White Paper WHP 169, September 2008, M. Armstrong, D. Flynn, M. Hammond, PAWAN Jahajpuria S. Jolly, R. Salmon.
  17. ^Jon Fingas (November 27, 2014),"James Cameron's 'Avatar' sequels will stick to 48 frames per second",Engadget,retrievedApril 15,2017
  18. ^Whaley, Sean (21 November 2018)."What is Frame Rate and Why is it Important to PC Gaming?".Retrieved5 August2021.
  19. ^Andy Edser (2024-03-26)."I used to be a frame rate snob but owning a Steam Deck has made me realise the error of my ways".PC Gamer.Retrieved2024-10-01.
  20. ^Writer, John Linneman Senior Staff; Foundry, Digital (2018-12-02)."PlayStation Classic review: the games are great but the emulation is really poor".Eurogamer.net.Retrieved2024-10-01.
  21. ^Simon, Niklaus; Long, Mai; Feng, Liu (2017).Video frame interpolation via adaptive separable convolution.ICCV.arXiv:1708.01692.
  22. ^Huaizu, Jiang; Deqing, Sun; Varun, Jampani; Ming-Hsuan, Yang; Erik, Learned-Miller; Jan, Kautz (2018).Super slomo: High quality estimation of multiple intermediate frames for video interpolation.ICCV.arXiv:1712.00080.
  23. ^Shurui, Gui; Chaoyue, Wang; Qihua, Chen; Dacheng, Tao (2020). "Featureflow: Robust video interpolation via structure-to-texture generation".2020 IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR).IEEE. pp. 14001–14010.doi:10.1109/CVPR42600.2020.01402.ISBN978-1-7281-7169-2.
  24. ^Myungsub, Choi; Heewon, Kim; Bohyung, Han; Ning, Xu; Kyoung, Mu Lee (2020)."Channel Attention is All You Need for Video Frame Interpolation".Proceedings of the AAAI Conference on Artificial Intelligence.34(7). AAAI: 10663–10671.doi:10.1609/aaai.v34i07.6693.
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