TV Framerates

TV uses different framerates than film:

Film 24 fps
PAL and SECAM 25 fps
TV NTSC 30 fps
TV NTSC color approximately 29.97 fps (30 * 1000 / 1001)
HDTV 24, 25, 30, 50 or 60 fps

NTSC is used in North America and Japan, PAL and SECAM are used in Europe and most other parts of the world. When adding color encoding to NTSC, the frame rate had to be adjusted by multiplying it with a factor 1000/1001 in order to avoid an interference between the color signal and the autio-carrier frequency - that’s why today we’ve got to deal with these odd 29.97 frames per seconds.

Since 25 and even 30 frames per seconds would result in a flickering image on a TV screen, the frames are split in two flieds. A TV frame is composed of scanlines, and the odd field contains just the odd scanlines, while the even field contains just the even scanlines. Thus, TV actually uses 50, 59.94 or 60 fields per second (This process is called interlacing).

Converting film to TV

This is called Telecine. For NTSC a process called 3:2 pulldown is used: The first film frame is held for three fields, the next one for two fields, the next ones for 3, 2, 3, 2… and so on. 24 frames of film thus make up 12 * 3 + 12 * 2 = 60 fields. For color NTSC this results in a framerate of 23.97 frames per second.

For PAL, two methods exist: Either the film is played back at 25 frames per second, or every 12th frame is held for two fields (which would preserve the 24 fps rate, but looks like if the film is held for 1/50 second twice a second, which is visible especially in slow pan-shots).

For HDTV both interlaced and non-interlaced (progressive) modes at different frame-rates are defined.

 
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