Last updated on January 23rd, 2024 at 02:17 am
A 3:2 pulldown is a method used to convert film footage to NTSC video footage.
You can’t directly convert film footage to video without any adjustment.
This is because film is shot at 24 frames per second. Video on the other hand is shot at 30 frames per second.
If film footage is transferred to video without proper conversion, the result is choppy or stuttery video. Why? Because the frame rates don’t match. So, 24 frames per second must be converted to 30 frames per second during the film-to-video conversion process.
How Does 3:2 Pulldown Work?
3:2 pulldown works by adding extra frames to the film footage during conversion,
To understand how 3:2 pulldown works, we must first understand how NTSC video works.
NTSC employs interlaced scanning. You need two video fields to make a single video frame. Half the lines are scanned in the first field. The other half is pushed to the second field.
During the film-to-video transfer process, the first film frame is converted to 2 video fields, The second frame is transferred to 3 video fields,
Then the third frame is converted to 2 video fields and the fourth frame to 3 video fields.
By adding an extra field to every even number video frame, 24 film frames are converted to 30 frames.
This is how it will look during the film-to-video transfer process.
- First film frame – 2 video fields
- Second film frame – 3 video fields
- Third film frame – 2 video fields
- Fourth film frame – 3 video fields
So, 4 frames of film are expanded to 10 video fields instead of the usual 8 fields in NTSC video. The result is 4 film frames are converted to 5 video frames as shown in the diagram below.
Isn’t that 2:3 conversion? Why is it called 3:2 then?
This is because years ago, the first film frame was converted to 3 video fields and the second frame to 2 video fields. That’s 3:2.
Then for technical reasons, it was switched to 2:3 but the old term was allowed to remain.
Other 3:2 Pulldown Applications
3:2 pulldown is not only used for transferring film footage to video.
Here are the other areas where this technique is used.
Broadcast
There will be instances when 24p video needs to be broadcast. When this is so, the video has to be first converted to 30 frames per second (fps) using 3:2 pulldown.
DVD Player
When feature films are converted to DVD, the film frame rate ( 24 fps) is maintained.
When the disc is played, the DVD player detects the film frame rate. It then applies a 3:2 pulldown and converts it to 30fps to be played on TV sets.
This is done to save storage space on the disc. Otherwise, 25% more disc space would be required to add new fields.
That space is instead used to improve video quality on a DVD.
Is 3:2 Pulldown Used on PAL Video?
PAL video has a frame rate of 25 frames per second (fps). Since this is close to the film frame rate of 24fps, no 3:2 pulldown is used.
Instead, the film is sped up by 4% to 25fps.
