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Three-two pull down
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Three-two pull down (3:2 pull down) is a term used in filmmaking and television production for the post-production process of transferring film to video.
It converts 24 frames per second into 29.97 frames per second, converting approximately every four frames into five frames plus a slight slow down in speed.[1] Film runs at a standard rate of 24 frames per second, whereas NTSC video has a signal frame rate of 29.97 frames per second. Every interlaced video frame has two fields for each frame. The three-two pull down is where the telecine adds a third video field (a half frame) to every second video frame, but the untrained eye cannot see the addition of this extra video field. In the figure, the film frames A–D are the true or original images since they have been photographed as a complete frame. The A, B, and D frames on the right in the NTSC footage are original frames. The third and fourth frames have been created by blending fields from different frames.
Video
[edit]2:3
[edit]
In the United States and other countries where television uses the 59.94 Hz vertical scanning frequency, video is broadcast at 29.97 frame/s. For the film's motion to be accurately rendered on the video signal, a telecine must use a technique called the 2:3 pull down (or a variant called 3:2 pull down) to convert from 24 to 29.97 frame/s.[2]
The term "pulldown" comes from the mechanical process of "pulling" (physically moving) the film downward within the film portion of the transport mechanism to advance it from one frame to the next at a repetitive rate (nominally 24 frames/s). This is accomplished in two steps.
The first step is to slow down the film motion by 1/1000 to 23.976 frames/s (or 24 frames every 1.001 seconds). This difference in speed is imperceptible to the viewer. For a two-hour film, play time is extended by 7.2 seconds.
The second step is distributing cinema frames into video fields. At 23.976 frame/s, there are four frames of film for every five frames of 29.97 Hz video:
These four frames needs to be "stretched" into five frames by exploiting the interlaced nature of video. Since an interlaced video frame is made up of two incomplete fields (one for the odd-numbered lines of the image, and one for the even-numbered lines), conceptually four frames need to be used in ten fields (to produce five frames).
The term "2:3" comes from the pattern for producing fields in the new video frames. The pattern of 2-3 is an abbreviation of the actual pattern of 2-3-2-3, which indicates that the first film frame is used in 2 fields, the second film frame is used in 3 fields, the third film frame is used in 2 fields, and the fourth film frame is used in 3 fields, producing a total of 10 fields, or 5 video frames.[3] If the four film frames are called A, B, C and D, the five video frames produced are A1-A2, B1-B2, B1-C2, C1-D2 and D1-D2. That is, frame A is used 2 times (in both fields of the first video frame); frame B is used 3 times (in both fields of the second video frame and in the odd field of the third video frame); frame C is used 2 times (in the even field of the third video frame, and in the odd field of the fourth video frame); and frame D is used 3 times (in the even field of the fourth video frame, and in both fields of the fifth video frame). The 2-3-2-3 cycle repeats itself completely after four film frames have been exposed.
3:2
[edit]
The alternative pattern of "3:2" is an abbreviation of the actual pattern of 3-2-3-2, which indicates that the first film frame is used in 3 fields, the second film frame is used in 2 fields, the third film frame is used in 3 fields, and the fourth film frame is used in 2 fields, producing a total of 10 fields, or 5 video frames.[2]
If the four film frames are called A, B, C and D, the five video frames produced are A1-A2, A1-B2, B1-C2, C1-C2 and D1-D2. That is, frame A is used 3 times (in both fields of the first video frame and in the odd field of the second video frame); frame B is used 2 times (in the even field of the second video frame, and in the odd field of the third video frame); frame C is used 3 times (in the even field of the third video frame and in both fields of the fourth video frame); and frame D is used 2 times (in both fields of the fifth video frame). The 3-2-3-2 cycle repeats itself completely after four film frames have been exposed.
In practice, there is no difference between the 2-3 and 3-2 patterns. A cycle that starts with film frame B yields a 3:2 pattern: B1-B2-B1-C2-C1-D2-D1-D2-A1-A2 (or 3-2-3-2). In fact, the "3-2" notation is misleading because according to SMPTE standards for every four-frame film sequence the first frame is scanned twice, not three times.[4]
Modern alternatives
[edit]
The above method is a "classic" 2:3 (a 2-3-2-3 cycle), which was used before frame buffers allowed for holding more than one frame. It has the disadvantage of creating two dirty frames (a mix from two different film frames, ex.: B1-C2 and C1-D2) in every five video frames.
The preferred method for doing a 2:3 is a 3-3-2-2 pattern (i.e. 3:3:2:2, 2:3:3:2 or 2:2:3:3) that creates only one dirty frame in every five. It produces A1-A2, A1-B2, B1-B2, C1-C2 and D1-D2, where only the second frame (A1-B2) is dirty.
While this method has a slight bit more judder, it allows for easier upconversion (the dirty frame can be dropped without losing information) and a better overall compression when encoding. Note that just fields are displayed—no frames hence no dirty frames—in interlaced displays such as on a CRT. Dirty frames may appear in other methods of displaying the interlaced video.[5]
Audio
[edit]The rate of NTSC video (initially monochrome, only, but soon thereafter monochrome and color) is 29.97 frames per second, or one-thousandth slower than 30 frame/s, due to the NTSC color encoding process which mandated that the line rate be a sub-multiple of the 3.579545 MHz color "burst" frequency, or 15734.2637 Hz (29.9700 Hz, frame rate), rather than the (60 Hz) ac "line locked" line rate of 15750 Hz (exactly 30 Hz, frame rate). This was done to maintain compatibility with black and white televisions.
Because of this 0.1% speed difference, when converting film to video, or vice versa, the sync will drift and the audio will end up out of sync by 3.6 seconds per hour. In order to correct this error, the audio can be either pulled up or pulled down. A pull up will speed up the sound by 0.1%, used for transferring video to film. A pull down will slow the audio speed down by 0.1%, necessary for transferring film to video.
See also
[edit]- 3D LUT
- Cintel, telecine equipment.
- Color motion picture film
- Color television
- Color suite
- Da Vinci Systems for color grading and video editing systems.
- Pandora International
- Digital intermediate
- Display resolution
- Faroudja, inventors of reverse telecine technologies.
- Film recorder
- Film restoration
- Film-out
- Gamma correction
- Hard disk recorder
- HDTV blur, factors causing HDTV Blur.
- Image scanner
- Keykode
- Kinescope
- Telecine
- Telecine (piracy), an unauthorized copy of a film created with a telecine.
- Telerecording (UK)
- Television
References
[edit]- ^ "What Is 3:2 Pulldown?". Extron. Retrieved 2025-03-05.
- ^ a b "About 2:3 Pulldown". download.autodesk.com. Retrieved 2025-03-05.
- ^ Stewart, Alan. 2-3 Pulldown Explained (PDF).
- ^ Poynton, Charles (2003). Charles Poynton, Digital Video and HDTV: Algorithms and Interfaces. Morgan Kaufmann. ISBN 9781558607927., page 430
- ^ US7612829B2, Chow, Wing-Chi, "2:2 and 3:2 pull-down detection techniques", issued 2009-11-03
Three-two pull down
View on GrokipediaOverview
Definition and Purpose
Three-two pulldown, also known as 3:2 pulldown, is a post-production technique used in filmmaking and television to transfer content originally captured at 24 frames per second (fps) on film to the 29.97 fps interlaced video standard of NTSC broadcast systems by selectively repeating video fields.[1][6] This method forms a core part of the telecine process, where motion picture film is scanned and converted into an electronic video format suitable for television airing or further editing.[6] The primary purpose of three-two pulldown is to reconcile the inherent frame rate mismatch between traditional cinematic film, which operates at 24 fps to achieve smooth motion while conserving film stock, and NTSC video standards, which use an interlaced format at approximately 30 fps (precisely 29.97 fps to accommodate the color subcarrier frequency and prevent interference).[7][1] By inserting additional fields without significantly altering playback speed—typically slowing the film by about 0.1% to align rates—this technique enables movies to be broadcast on television with minimal distortion, preserving the original timing and artistic intent.[7][1] In the basic telecine process, each film frame is scanned into two interlaced video fields (one for odd lines, one for even lines), but to match the higher video field rate of 59.94 fields per second, pulldown inserts extra fields through repetition.[6][7] The "3:2" ratio specifically describes the repeating pattern where, over a sequence of four film frames, ten video fields are generated (three fields from the first frame, two from the second, three from the third, and two from the fourth), ensuring the overall timing remains approximately synchronized.[1][6] This field repetition pattern, while introducing minor motion artifacts, effectively bridges the rate conversion without resorting to uniform speedup or slowdown that could affect audio pitch or visual fluidity.[7]Historical Development
The three-two pulldown technique emerged in the 1950s amid the rapid expansion of U.S. television broadcasting, addressing the fundamental mismatch between 24 frames per second theatrical film and the 30 frames per second NTSC video standard. Developed by RCA engineers to convert film content for live telecine transmission, it allowed networks to integrate movies into programming schedules without significant speed alterations. Early adoption occurred at major broadcasters like NBC, which utilized RCA's systems to air Hollywood features, marking a pivotal shift from predominantly live content to film-based shows.[8] A critical advancement came in 1953 with the FCC's approval of the NTSC color television standard, which introduced a subtle frame rate reduction to 29.97 fps to prevent the new color subcarrier from interfering with audio signals and causing visible artifacts. This adjustment necessitated refined implementation of 3:2 pulldown in telecine equipment, standardizing the process for color-compatible broadcasts and ensuring smooth integration of monochrome film libraries. RCA's innovations in this era, including advanced film chain systems, played a central role in enabling networks such as CBS and NBC to deliver colorized film content reliably to viewers.[9][4] By the 1970s, three-two pulldown had become embedded in consumer video production workflows, particularly with the launch of VHS formats in 1976, where telecine transfers routinely applied the technique to encode films for home playback on NTSC VCRs. This extension democratized access to cinematic content beyond theaters. The method endured into the digital age for DVD and early streaming, but its prominence waned in the 2000s as high-definition broadcasting prioritized 24p native formats, reducing reliance on pulldown through inverse telecine and progressive scanning.[10] The technique's historical significance lies in facilitating the mass dissemination of Hollywood films via television, transforming evening broadcasts into cultural staples for millions. However, the inherent judder from uneven field repetition created a distinctive motion artifact, often recognized as the "filmed on TV" aesthetic that differentiated broadcast movies from smoother video productions.[11]Technical Mechanism
Frame Rate Conversion Process
The frame rate conversion process in three-two pulldown begins with advancing the film through a projector at a rate of 23.976 frames per second to align with NTSC video standards.[1] Each film frame is then scanned by the telecine equipment into two interlaced fields: one containing the odd-numbered lines and the other the even-numbered lines, capturing the full image progressively but outputting it in an interlaced format for compatibility with broadcast video.[12] This scanning occurs in real time, with the telecine machine synchronizing the film's mechanical pull-down motion—where the film is held steady for exposure—with the generation of video fields at 59.94 fields per second (equivalent to 29.97 frames per second interlaced).[13] To achieve the target output rate, extra fields must be inserted since 24 film frames produce only 48 fields, while 29.97 fps interlaced video requires 60 fields per second. The timing is calibrated such that 24 film frames at 23.976 fps occupy exactly 1 second, matching the duration of 30 video frames at 29.97 fps, thus preserving the original playback speed without alteration.[1] This 0.1% slowdown from a nominal 24 fps to 23.976 fps compensates for the NTSC video rate being slightly slower than an exact 30 fps, ensuring temporal alignment through field duplication rather than frame blending or speed adjustment.[12] The pulldown process targets individual fields rather than complete frames to reduce motion artifacts like judder, as each video frame comprises two sequentially displayed fields, each lasting 1/59.94 seconds. Telecine machines, such as the Spirit DataCine, facilitate this conversion in real time by integrating high-resolution scanning with digital processing. These devices scan the film at up to 2K resolution and output interlaced SD or HD video signals, maintaining synchronization between the film's advancement and the video field's timing to produce seamless 59.94-field-per-second output.[13] The standard insertion method for the extra fields is the 3:2 pulldown pattern.Field Repetition Patterns
In the standard 3:2 pulldown process, film frames are converted to interlaced video fields through a repeating pattern of duplications to match the higher frame rate. Specifically, the first film frame (A) contributes three fields: its top field (A1), bottom field (A2), and a repetition of the top field (A1). The subsequent film frame (B) contributes two fields: bottom (B2) then top (B1). This alternation continues with the third frame (C) providing three fields: bottom (C2), top (C1), and a repetition of the bottom (C2); the fourth (D) providing two: top (D1), bottom (D2), resulting in 10 video fields derived from 4 film frames overall.[1] The precise field mapping for one complete cycle follows this sequence, where each film frame's progressive content is separated into odd (top) and even (bottom) fields for interlaced output:| Video Field | Source Field |
|---|---|
| 1 (odd) | A top |
| 2 (even) | A bottom |
| 3 (odd) | A top (repeat) |
| 4 (even) | B bottom |
| 5 (odd) | B top |
| 6 (even) | C bottom |
| 7 (odd) | C top |
| 8 (even) | C bottom (repeat) |
| 9 (odd) | D top |
| 10 (even) | D bottom |
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