Frame rate

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Frame rate, or frame frequency, is the frequency (rate) at which an imaging device produces unique consecutive images called frames. The term applies equally well to computer graphics, video cameras, film cameras, and motion capture systems. Frame rate is most often expressed in frames per second (FPS), and in progressive scan monitors as hertz (Hz).

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Frame rates in film and television

There are currently (2010) three main frame rate standards in the TV and movie-making business: 24p, 25p, and 30p. However there are many variations on these as well as newer emerging standards.

  • 50i (50 interlaced fields = 25 frames) is the standard video field rate per second for PAL and SECAM television.
  • 60i (actually 59.94, or 60 x 1000/1001 to be more precise; 60 interlaced fields = 29.97 frames) is the standard video field rate per second for NTSC television (e.g. in the US), whether from a broadcast signal, DVD, or home camcorder. This interlaced field rate was developed separately by Farnsworth and Zworykin in 1934,[1] and was part of the NTSC television standards mandated by the FCC in 1941. When NTSC color was introduced in 1953, the older rate of 60 fields per second was reduced by a factor of 1000/1001 to avoid interference between the chroma subcarrier and the broadcast sound carrier.
  • 30p, or 30-frame progressive, is a noninterlaced format and produces video at 30 frames per second. Progressive (noninterlaced) scanning mimics a film camera's frame-by-frame image capture. The effects of inter-frame judder are less noticeable than 24p yet retains a cinematic-like appearance. Shooting Video in 30p mode gives no interlace artifacts but can introduce judder on image movement and on some camera pans. The widescreen film process Todd-AO used this frame rate in 1954–1956.[2]
  • The 24p frame rate is also a noninterlaced format, and is now widely adopted by those planning on transferring a video signal to film. Film and video makers use 24p even if their productions are not going to be transferred to film, simply because of the on-screen "look" of the (low) frame rate which matches native film. When transferred to NTSC television, the rate is effectively slowed to 23.976 frame/s, and when transferred to PAL or SECAM it is sped up to 25 frame/s. 35 mm movie cameras use a standard exposure rate of 24 frames per second, though many cameras offer rates of 23.976 frame/s for NTSC television and 25 frame/s for PAL/SECAM. The 24 frame/s rate became the de facto standard for sound motion pictures in the mid-1920s.[3]

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