AskDefine | Define Judder

Dictionary Definition

judder v : shake or vibrate rapidly and intensively; "The old engine was juddering" [syn: shake]

Extensive Definition

Telecine (, also /ˌtɛləˈsiːn/ — "tel-e-Sin-ee"; "tel-e-Sin-a" as 'cine' is the same root as in 'cinema'; also "tele-seen".) is the process of transferring motion picture film into video form. The term is also used to refer to the equipment used in the process.
Telecine enables a motion picture, captured originally on film, to be viewed with standard video equipment, such as televisions, video cassette decks or computers. This allows producers and distributors working in film to release their products on video and allows producers to use video production equipment to complete their film projects. The word “Telecine” is a combination of “television” and “cinema.” Within the film industry, it is also referred to as a TK, as TC is already used to designate time code.

History of telecine

With the advent of popular television, broadcasters realized they needed more than live programming. By turning to film-originated material, they would have access to the wealth of films made for the cinema in addition to recorded television programming on film that could be aired at different times. However, the difference in frame rates between film (generally 24 frame/s) and television (30 or 25 frame/s) meant that simply playing a film into a television camera would result in flickering when the film frame was changed in mid-field of the TV frame.
Originally the kinescope was used to record the image off of a television display to film, synchronized to the TV scan rate. This could then be re-played directly into a video camera for re-display. Non-live programming could also be filmed using the same cameras, edited mechanically as normal, and then played back for TV. As the film was run at the same speed as the television, the flickering was eliminated. Various displays, including projectors for these "video rate films", slide projectors and movie cameras were often combined into a "Film Chain", allowing the broadcaster to cue up various forms of media and switch between them by moving a mirror or prism. Color was supported by using a multi-tube video camera and prisms to separate the original color signal and feeding the red, green and blue to separate tubes.
However, this still left film shot at cinema rates as a problem. The obvious solution is to simply speed up the film to match the television frame rates, but this, at least in the case of NTSC, is rather obvious to the eye and ear. This problem is not difficult to fix, however; the solution being to periodically play a selected frame twice. For NTSC, the difference in frame rates can be corrected by showing every 4th frame of film twice, although this does require the sound to be handled separately to avoid "skipping" effects. A more convincing technique is to use "2:3 pulldown", which turns every other frame of the film into three fields of video, which results in a much smoother display. PAL uses a similar system, "2:2 pulldown". These projectors could be included into existing film chain systems, allowing cinematic films to be played directly to television. With the introduction of videotape into television processing in the 1950s, it became practical to record telecined movies to videotape for later playback. This eliminated the need for the special projectors and cameras in the broadcast studio.
Since that time, telecine has primarily been a film-to-videotape process, as opposed to film-to-air. Changes since the 1950s have primarily been in terms of equipment and physical formats, the basic concept remains the same. Home videotapes of movies used this technique, and it is not uncommon to find telecined DVDs when the source was originally recorded to videotape. The same is not true for modern DVDs of cinematic movies, which are generally recorded in their original frame rate — in these cases the DVD player itself applies telecining as required to match the capabilities of the television.

Frame rate differences

The most complex part of telecine is the synchronization of the mechanical film motion and the electronic video signal. Every time the video part of the telecine samples the light electronically, the film part of the telecine must have a frame in perfect registration and ready to photograph. This is relatively easy when the film is photographed at the same frame rate as the video camera will sample, but when this is not true, a sophisticated procedure is required to change frame rate.
To avoid the synchronisation issues, higher end establishments now use a scanning system rather than just a telecine system. This allows them to scan a distinct frame of digital video for each frame of film, providing higher quality than a telecine system would be able to achieve. Normally, best results are then achieved by using a smoothing (interpolating algorithm) rather than a frame duplication algorithm (such as 3:2 pulldown, etc) to adjust for speed differences between the film and video frame rate.

2:2 pulldown

In countries that use the PAL or SECAM video standards, film destined for television is photographed at 25 frames per second. The PAL video standard broadcasts at 25 frames per second, so the transfer from film to video is simple; for every film frame, one video frame is captured.
Theatrical features originally photographed at 24 frame/s are simply sped up by 4% to 25 frame/s. While this is usually not noticed in the picture it causes a slightly noticeable increase in audio pitch by about one semitone, which is sometimes corrected using a pitch shifter, though pitch shifting is a recent innovation and supersedes an alternative method of telecine for 25 frame/s formats. However, a difference between the two is rarely noticed unless the original audio is compared side by side with the pitched audio.
2:2 pulldown is also used to transfer shows and movies, photographed at 30 frames per second, like "Friends" and "Oklahoma!", to NTSC video, which has 60 Hz scanning rate.

2:2:2:2:2:2:2:2:2:2:2:3 pulldown

Although the 4% speed increase has been standard since the early days of PAL and SECAM television, recently a new technique has gained popularity. This method converts every film frame to two video fields, except that every 12th frame is repeated, fitting exactly within 25 frames (50 fields) of video per second. The speed and pitch of the telecined presentation are identical to that of the original film.
This pulldown method is sometimes used in order to convert 24 frame/s material to 25 frame/s. Usually, this involves a film to PAL transfer without the aforementioned 4% speedup. For film at 24 frame/s, there are 24 frames of film for every 25 frames of PAL video. In order to accommodate this mismatch in frame rate, 24 frames of film have to be distributed over 50 PAL fields. This can be accomplished by inserting a pulldown field every 12 frames, thus effectively spreading 12 frames of film over 25 fields (or “12.5 frames”) of PAL video.
This method was born out of a frustration with the faster, higher pitched soundtracks that traditionally accompanied films telecined for PAL and SECAM audiences. More motion pictures are beginning to be telecined this way. It is particularly suited for films where the soundtrack is of special importance.

2:3 pulldown

In the United States and other countries that use the NTSC television standard, film is generally photographed at 24 frame/s. Color NTSC video is broadcast at 29.97 frame/s. For the film's motion to be accurately rendered on the video signal, an NTSC telecine must use a technique called the 2:3 pulldown to convert from 24 to 29.97 frame/s.
The process of converting 24 frame/s material to 29.97 frame/s is known as 2:3 pulldown (sometimes also called 3:2 pulldown). The term “pulldown” comes from the mechanical process of “pulling” the film down to advance it from one frame to the next at a repetitive rate (nominally 24 frame/s). This is accomplished in two steps. The first step is to slow down the film motion by 1/1001. This speed change is unnoticeable to the viewer, and makes the film travel at 23.976 frame/s (or 7.2 seconds longer in a 2-hour movie).
The second step of the 2:3 pulldown is distributing cinema frames into video fields. At 23.976 frame/s, there are four frames of film for every five frames of NTSC video:
\frac = \frac
These four frames are “stretched” into five by exploiting the interlaced nature of NTSC video. For every NTSC frame, there are actually two complete images or fields, one for the odd-numbered lines of the image, and one for the even-numbered lines. There are, therefore, ten fields for every 4 film frames, and the telecine alternately places one film frame across two fields, the next across three, the next across two, and so on. The cycle repeats itself completely after four film frames have been exposed, and in the telecine cycle these are called the A, B, C, and D frames, thus:
A 3:2 pattern is identical to this except that it is shifted by one frame. For instance, starting with film frame B, followed by frame C, yields a 3:2 pattern (B-B-B-C-C). In other words, there is no difference between the two — it is only a matter of reference. In fact, the "3:2 pulldown" notation is misleading because according to SMPTE standards the first frame of every four-frame film sequence (the A-frame) is associated with the first and second fields of one video frame, and is scanned twice, not three times.
The above method is a "classic" 2:3, which was used before frame buffers allowed for holding more than one frame. The preferred method for doing a 2:3 creates only one dirty frame in every 5 (i.e. 3:3:2:2 or 2:3:3:2 or 2:2:3:3); 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. The 2:3:3:2 pattern is supported by the Panasonic DVX-100B video camera under the name "Advanced Pulldown".

Other pulldown patterns

Similar techniques must be used for films shot at “silent speeds” of less than 24 frame/s (about 18frame/s), which include most silent movies themselves as well as many home movies. 16 frame/s (actually 15.985) to NTSC 30 frame/s (actually 29.97), pulldown should be 3:4:4:4; 16 frame/s to PAL, pulldown should be 3:3:3:3:3:3:3:4; 18 frame/s (actually 17.982) to NTSC, pulldown should be 3:3:4; 20 frame/s (actually 19.980) to NTSC, pulldown should be 3:3.

Telecine judder

see also Motion interpolation The “2:3 pulldown” telecine process creates a slight error in the video signal compared to the original film frames that can be seen in the above image. This is one reason why NTSC films viewed on typical home equipment may not appear as smooth as when viewed in a cinema. The phenomenon is particularly apparent during slow, steady camera movements which appear slightly jerky when telecined. This process is commonly referred to as telecine judder. Reversing the 2-3 pulldown telecine is discussed below.
PAL material in which 2:2:2:2:2:2:2:2:2:2:2:3 pulldown has been applied, suffers from a similar lack of smoothness, though this effect is not usually called “telecine judder”. Effectively, every 12th film frame is displayed for the duration of 3 PAL fields (60 milliseconds), whereas the other 11 frames are all displayed for the duration of 2 PAL fields (40 milliseconds). This causes a slight “hiccup” in the video about twice a second.

Reverse telecine (a.k.a. IVTC/inverse telecine)

Some DVD players, line doublers, and personal video recorders are designed to detect and remove 2-3 pulldown from interlaced video sources, thereby reconstructing the original 24 frame/s film frames. This technique is known as “reverse” or “inverse” telecine. Benefits of reverse telecine include high-quality non-interlaced display on compatible display devices and the elimination of redundant data for compression purposes.
Reverse telecine is crucial when acquiring film material into a digital non-linear editing system such as an Avid or Final Cut Pro, since these machines produce negative cut lists which refer to specific frames in the original film material. When video from a telecine is ingested into these systems, the operator usually has available a “telecine trace,” in the form of a text file, which gives the correspondence between the video material and film original. Alternatively, the video transfer may include telecine sequence markers “burned in” to the video image along with other identifying information such as time code.
It is also possible, but more difficult, to perform reverse telecine without prior knowledge of where each field of video lies in the 2-3 pulldown pattern. This is the task faced by most consumer equipment such as line doublers and personal video recorders. Ideally, only a single field needs to be identified, the rest following the pattern in lock-step. However, the 2-3 pulldown pattern does not necessarily remain consistent throughout an entire program. Edits performed on film material after it undergoes 2-3 pulldown can introduce “jumps” in the pattern if care is not taken to preserve the original frame sequence (this often happens during the editing of television shows and commercials in NTSC format). Most reverse telecine algorithms attempt to follow the 2-3 pattern using image analysis techniques, e.g. by searching for repeated fields.
Algorithms that perform 2-3 pulldown removal also usually perform the task of deinterlacing. It is possible to algorithmically determine whether video contains a 2-3 pulldown pattern or not, and selectively do either reverse telecine (in the case of film-sourced video) or deinterlacing (in the case of native video sources).
Some product sheets refer to reverse telecine as “reverse 2:3 pulldown.”

Telecine hardware

Flying spot scanner

In the United Kingdom, Rank Precision Industries was experimenting with the flying-spot scanner (FSS), which inverted the cathode ray tube (CRT) concept of scanning using a television screen. The CRT emits a pixel-sized electron beam which is converted to a photon beam through the phosphors coating the envelope. This dot of light is then focused by a lens onto the film's emulsion, and finally collected by a pickup device. In 1950 the first Rank flying spot monochrome telecine was installed at the BBC's Lime Grove studios. The advantage of the FSS is that colour analysis is done after scanning, so there can be no registration errors as can be produced by vidicon tubes where scanning is done after colour separation — it also allows simpler dichroics to be used.
In a flying spot scanner (FSS) or cathode-ray tube (CRT) telecine, a pixel-sized light beam is projected through exposed and developed motion picture film (either negative or positive) at a phosphor-coated envelope. This beam of light “scans” across the film image from left to right to record the vertical frame information. Horizontal scanning of the frame was then accomplished by moving the film past the CRT beam. This beam passes through the film image, projecting it pixel-by-pixel onto the pickup (phosphor-coated envelope). The light from the CRT passes through the film and is separated by dichroic mirrors and filters into red, green and blue bands. Photomultiplier tubes or avalanche photodiodes convert the light into separate red, green and blue electrical signals for further electronic processing. This can be accomplished in “real time”, 24 frames a second (or in some cases faster). Rank Precision-Cintel introduced the “Mark” series of FSS telecines. During this time advances were also made in CRTs, with increased light output producing a better signal-to-noise ratio and so allowing negative film to be used. The problem with flying-spot scanners was the difference in frequencies between television field rates and film frame rates. This was solved first by the Mk.I Polygonal Prism system, which was optically sychronised to the television frame rate by the rotating prism and could be run at any frame rate. This was replaced by the Mk.II Twin Lens, and then around 1975, by the Mk.III Hopping Patch (jump scan). The Mk.III series progressed from the original “jump scan” interlace scan to the Mk.IIIB which used a progressive scan and included a digital scan converter (Digiscan) to output interlaced video. The Mk.IIIC was the most popular of the series and used a next generation Digiscan plus other improvements.
The "Mark" series was then replaced by the Ursa (1989), the first in their line of telecines capable of producing digital data in 4:2:2 color space. The Ursa Gold (1993) stepped this up to 4:4:4 and then the Ursa Diamond (1997), which incorporated many third-party improvements on the Ursa system.

CCD

Judder in Czech: Telecine
Judder in Danish: Telecine
Judder in German: Filmabtaster
Judder in French: Télécinéma
Judder in Italian: Telecinema
Judder in Dutch: Telecine
Judder in Japanese: テレシネ
Judder in Polish: TeleCine
Judder in Russian: Телекино
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