3: 2 pull-down

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3: 2 pull-down is a process for the conversion of a film signal in an NTSC - television signal .

Since the NTSC standard works at 29.97 frames per second ( fps ), but movies are recorded at 24 fps, the conversion of a film signal into an NTSC television signal must be carried out in two steps. First, the film signal must be slowed down by about 0.1% (more precisely: 1000 seconds of the original film material are played every 1001 seconds). This difference is so small that it is not noticeable to a viewer. This results in a speed of 23.976 frames per second for the film signal and thus 4 individual images in the film signal are compared to 5 individual images in the NTSC signal:

In a second step, the four individual images are stretched to five images with the aid of the interlace method . A full picture is divided into fields. Two or three fields are generated alternately from each cinema picture: The first full picture is shown two fields long, the second full picture three fields long, the third full picture again two fields, etc. This results in the desired 59.94 fields (= 29.97 Frames) per second for NTSC. With settings with a fixed camera or with fast pans this is hardly noticeable, with slow camera pans, however, there is a noticeable jerking in the sequence of movements.

With digital reception or playback devices (digital television, DVD, video CD), the 3: 2 pull-down is usually only carried out in the end device, the actual digital data stream contains 23.976 full images per second and a flag that indicates the pull-down in the end device caused. This is because the two full images “mixed” from different original full images (3rd and 4th image of the group of five), which result from the pull-down in each full image group of five, cannot be compressed well. In the opposite case, when storing a video signal that was created by pull-down, an Inverse Telecine should therefore first be carried out in the interests of good data compression , i.e. the pull-down should be reversed. Most digital video recorders for NTSC signals automatically detect pull-downs and then perform an inverse telecine before they are stored (e.g. on an integrated hard drive).

3: 2 pull-down Pulldown diagram

See also