3:2 Pulldown / Cadence
Definition
3:2 pulldown, also written 2:3, is the process that converts 24 fps film to 59.94 Hz interlaced video (29.97 fps) by spreading four film frames over ten video fields in a 2-3-2-3 pattern. The film is also slowed by 0.1% to 23.976 fps, the rate that ITU-R BT.709 includes for compatibility with pull-down. The uneven repetition gives a recognisable judder on camera movements. Inverse telecine removes the repeated fields and restores the original 24 frames for editing or projection. In 50 Hz regions, 24 fps film is usually played at 25 fps, about 4% faster, with each frame shown as two fields (2:2 pulldown), so 3:2 cadence is specific to 60 Hz systems. Mixed cadences in a playout chain cause stutter that frame blending does not fully hide.
In the field
24p content that judders on a 60 Hz output has either a wrong pulldown or a pulldown applied twice. The usual fix is to output the native cadence from the media server when the display accepts it, or to apply a proper inverse telecine before any further conversion. On 50 Hz projects, the content is often converted to 25 fps before the show.
Sources
- ITU-R BT.709-6 : cadence 24/1,001 (23,976 Hz) prévue pour la compatibilité avec le pull-down NTSC · itu.int
- Wikipédia, Three-two pull down : quatre images réparties sur dix trames, ralentissement de 0,1 % (pointeur secondaire) · en.wikipedia.org
- Wikipédia, Telecine : accélération de 24 à 25 fps en 50 Hz (pulldown 2:2), télécinéma inverse (pointeur secondaire) · en.wikipedia.org