Reverse 3:2 pulldown detects and removes the repeated fields created when 24 fps film is transferred to interlaced video, rebuilding the original film frames as progressive video. It is also called reverse telecine, inverse telecine (IVTC), or 3:2 pullup. It works when the source still has a recoverable film cadence; it is not a general-purpose fix for every interlaced video.
Why 3:2 pulldown is used
Film commonly runs at 24 frames per second, while the legacy NTSC interlaced video system runs at approximately 60 fields per second, or 29.97 two-field frames per second. Those rates do not match, so a film-to-video transfer distributes each film frame across a repeating pattern of video fields. This process is called pulldown or telecine. AJA describes the relevant film-rate output in its FS3 manual.
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Because some film frames contribute two fields and others three, grouping the fields into ordinary two-field video frames can pair fields from different moments in the film. Reverse pulldown detects the repeating pattern and recombines matching fields to recover progressive film frames.
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Consider four consecutive film frames, A, B, C, and D. Their fields can be distributed across five interlaced video frames as AA, BB, BC, CD, DD. The BC frame combines fields from two different film moments, so viewing it as a single image can reveal comb-like horizontal edges on moving objects.
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The pattern’s starting phase and field dominance—the order in which the two fields occur in time—matter when reconstructing the frames. The labels “3:2” and “2:3” can describe the same repeating cadence family from different starting points or conventions. Autodesk’s documentation explains why a pullup workflow needs the cadence start and field dominance: 3:2 pullup and field dominance.
What reverse telecine produces
When cadence detection succeeds, reverse telecine removes the redundant field pattern and turns five interlaced video frames back into four progressive film frames. The result is commonly described as 24p or 23.98p, depending on the source and video convention. For example, AJA’s FS3 documentation lists 23.98p or PsF23.98 output for its supported inputs; that is a device-specific example, not a universal output specification.
Reverse telecine versus deinterlacing
| Method | Best suited to | What it does |
|---|---|---|
| Reverse telecine (IVTC) | Film-originated footage with a detectable, recoverable 3:2 cadence | Matches fields from the same film moments and restores the progressive film-rate sequence. |
| Deinterlacing | Native interlaced video, or footage where film cadence cannot be recovered | Creates progressive images from interlaced fields without relying on the film pulldown pattern. |
They solve different problems. Applying inverse telecine to native interlaced video does not restore a film sequence that was never there. Conversely, ordinary deinterlacing may not recover the original film frames as accurately as cadence-aware reconstruction when pulldown is intact. Mixed sources may need film-mode detection on film-originated sections and video-mode deinterlacing on native-video sections, as discussed by Analog Devices.
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Reverse pulldown is useful when film-originated material was stored or delivered with interlaced pulldown and you need the original progressive frames for film-rate editing or compositing. Reliable reconstruction depends on a consistent, detectable cadence.
- Cadence breaks: An edit, dropped frame, or other interruption can disrupt the repeating pattern. Detection may take time to lock again.
- Mixed film and video: Some material contains both film-originated sections and native interlaced video, which may require different processing modes.
- Non-film footage: Without a film pulldown cadence to recover, use a suitable deinterlacing method instead.
- Format and field-order limits: Hardware support depends on the input format, supported cadence, field order, and output configuration.
These constraints are implementation-specific. AJA’s FS3 manual, for example, describes reverse telecine for specified interlaced inputs with consistent 3:2 or 2:3:3:2 pulldown and selected 23.98 progressive or PsF output. It says the converter needs approximately 10 incoming frames to detect cadence and may need a similar interval after a cadence discontinuity. Do not assume those figures or supported formats apply to other converters or editing software.
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What to check before converting footage
- Confirm the source: Check that the footage originated as film and was transferred with pulldown, rather than recorded as native interlaced video.
- Check cadence and field order: Use a tool that can detect the cadence or lets you set its start phase and field dominance. A wrong setting can pair fields from different moments.
- Choose the intended output rate: Match the project to the recovered film rate—often 23.98p in digital NTSC workflows, though some sources are described as 24p.
- Inspect motion and edits: Check moving edges for combing or duplicated frames, especially around cuts and cadence breaks. If the pattern is mixed or cannot be recovered, use deinterlacing for the affected sections.
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